/* SPDX-License-Identifier: GPL-2.0 */ /* * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst * * Copyright (c) 2022 Meta Platforms, Inc. and affiliates. * Copyright (c) 2022 Tejun Heo * Copyright (c) 2022 David Vernet */ #include #include "ext_idle.h" static DEFINE_RAW_SPINLOCK(scx_sched_lock); /* * NOTE: sched_ext is in the process of growing multiple scheduler support and * scx_root usage is in a transitional state. Naked dereferences are safe if the * caller is one of the tasks attached to SCX and explicit RCU dereference is * necessary otherwise. Naked scx_root dereferences trigger sparse warnings but * are used as temporary markers to indicate that the dereferences need to be * updated to point to the associated scheduler instances rather than scx_root. */ struct scx_sched __rcu *scx_root; /* * All scheds, writers must hold both scx_enable_mutex and scx_sched_lock. * Readers can hold either or rcu_read_lock(). */ static LIST_HEAD(scx_sched_all); #ifdef CONFIG_EXT_SUB_SCHED static const struct rhashtable_params scx_sched_hash_params = { .key_len = sizeof_field(struct scx_sched, ops.sub_cgroup_id), .key_offset = offsetof(struct scx_sched, ops.sub_cgroup_id), .head_offset = offsetof(struct scx_sched, hash_node), }; static struct rhashtable scx_sched_hash; #endif /* * During exit, a task may schedule after losing its PIDs. When disabling the * BPF scheduler, we need to be able to iterate tasks in every state to * guarantee system safety. Maintain a dedicated task list which contains every * task between its fork and eventual free. */ static DEFINE_RAW_SPINLOCK(scx_tasks_lock); static LIST_HEAD(scx_tasks); /* ops enable/disable */ static DEFINE_MUTEX(scx_enable_mutex); DEFINE_STATIC_KEY_FALSE(__scx_enabled); DEFINE_STATIC_PERCPU_RWSEM(scx_fork_rwsem); static atomic_t scx_enable_state_var = ATOMIC_INIT(SCX_DISABLED); static DEFINE_RAW_SPINLOCK(scx_bypass_lock); static cpumask_var_t scx_bypass_lb_donee_cpumask; static cpumask_var_t scx_bypass_lb_resched_cpumask; static bool scx_init_task_enabled; static bool scx_switching_all; DEFINE_STATIC_KEY_FALSE(__scx_switched_all); static atomic_long_t scx_nr_rejected = ATOMIC_LONG_INIT(0); static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0); #ifdef CONFIG_EXT_SUB_SCHED /* * The sub sched being enabled. Used by scx_disable_and_exit_task() to exit * tasks for the sub-sched being enabled. Use a global variable instead of a * per-task field as all enables are serialized. */ static struct scx_sched *scx_enabling_sub_sched; #else #define scx_enabling_sub_sched (struct scx_sched *)NULL #endif /* CONFIG_EXT_SUB_SCHED */ /* * A monotonically increasing sequence number that is incremented every time a * scheduler is enabled. This can be used to check if any custom sched_ext * scheduler has ever been used in the system. */ static atomic_long_t scx_enable_seq = ATOMIC_LONG_INIT(0); /* * Watchdog interval. All scx_sched's share a single watchdog timer and the * interval is half of the shortest sch->watchdog_timeout. */ static unsigned long scx_watchdog_interval; /* * The last time the delayed work was run. This delayed work relies on * ksoftirqd being able to run to service timer interrupts, so it's possible * that this work itself could get wedged. To account for this, we check that * it's not stalled in the timer tick, and trigger an error if it is. */ static unsigned long scx_watchdog_timestamp = INITIAL_JIFFIES; static struct delayed_work scx_watchdog_work; /* * For %SCX_KICK_WAIT: Each CPU has a pointer to an array of kick_sync sequence * numbers. The arrays are allocated with kvzalloc() as size can exceed percpu * allocator limits on large machines. O(nr_cpu_ids^2) allocation, allocated * lazily when enabling and freed when disabling to avoid waste when sched_ext * isn't active. */ struct scx_kick_syncs { struct rcu_head rcu; unsigned long syncs[]; }; static DEFINE_PER_CPU(struct scx_kick_syncs __rcu *, scx_kick_syncs); /* * Direct dispatch marker. * * Non-NULL values are used for direct dispatch from enqueue path. A valid * pointer points to the task currently being enqueued. An ERR_PTR value is used * to indicate that direct dispatch has already happened. */ static DEFINE_PER_CPU(struct task_struct *, direct_dispatch_task); static const struct rhashtable_params dsq_hash_params = { .key_len = sizeof_field(struct scx_dispatch_q, id), .key_offset = offsetof(struct scx_dispatch_q, id), .head_offset = offsetof(struct scx_dispatch_q, hash_node), }; static LLIST_HEAD(dsqs_to_free); /* string formatting from BPF */ struct scx_bstr_buf { u64 data[MAX_BPRINTF_VARARGS]; char line[SCX_EXIT_MSG_LEN]; }; static DEFINE_RAW_SPINLOCK(scx_exit_bstr_buf_lock); static struct scx_bstr_buf scx_exit_bstr_buf; /* ops debug dump */ static DEFINE_RAW_SPINLOCK(scx_dump_lock); struct scx_dump_data { s32 cpu; bool first; s32 cursor; struct seq_buf *s; const char *prefix; struct scx_bstr_buf buf; }; static struct scx_dump_data scx_dump_data = { .cpu = -1, }; /* /sys/kernel/sched_ext interface */ static struct kset *scx_kset; /* * Parameters that can be adjusted through /sys/module/sched_ext/parameters. * There usually is no reason to modify these as normal scheduler operation * shouldn't be affected by them. The knobs are primarily for debugging. */ static unsigned int scx_slice_bypass_us = SCX_SLICE_BYPASS / NSEC_PER_USEC; static unsigned int scx_bypass_lb_intv_us = SCX_BYPASS_LB_DFL_INTV_US; static int set_slice_us(const char *val, const struct kernel_param *kp) { return param_set_uint_minmax(val, kp, 100, 100 * USEC_PER_MSEC); } static const struct kernel_param_ops slice_us_param_ops = { .set = set_slice_us, .get = param_get_uint, }; static int set_bypass_lb_intv_us(const char *val, const struct kernel_param *kp) { return param_set_uint_minmax(val, kp, 0, 10 * USEC_PER_SEC); } static const struct kernel_param_ops bypass_lb_intv_us_param_ops = { .set = set_bypass_lb_intv_us, .get = param_get_uint, }; #undef MODULE_PARAM_PREFIX #define MODULE_PARAM_PREFIX "sched_ext." module_param_cb(slice_bypass_us, &slice_us_param_ops, &scx_slice_bypass_us, 0600); MODULE_PARM_DESC(slice_bypass_us, "bypass slice in microseconds, applied on [un]load (100us to 100ms)"); module_param_cb(bypass_lb_intv_us, &bypass_lb_intv_us_param_ops, &scx_bypass_lb_intv_us, 0600); MODULE_PARM_DESC(bypass_lb_intv_us, "bypass load balance interval in microseconds (0 (disable) to 10s)"); #undef MODULE_PARAM_PREFIX #define CREATE_TRACE_POINTS #include static void run_deferred(struct rq *rq); static bool task_dead_and_done(struct task_struct *p); static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags); static void scx_disable(struct scx_sched *sch, enum scx_exit_kind kind); static bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, const char *fmt, va_list args); static __printf(4, 5) bool scx_exit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, const char *fmt, ...) { va_list args; bool ret; va_start(args, fmt); ret = scx_vexit(sch, kind, exit_code, fmt, args); va_end(args); return ret; } #define scx_error(sch, fmt, args...) scx_exit((sch), SCX_EXIT_ERROR, 0, fmt, ##args) #define scx_verror(sch, fmt, args) scx_vexit((sch), SCX_EXIT_ERROR, 0, fmt, args) #define SCX_HAS_OP(sch, op) test_bit(SCX_OP_IDX(op), (sch)->has_op) static long jiffies_delta_msecs(unsigned long at, unsigned long now) { if (time_after(at, now)) return jiffies_to_msecs(at - now); else return -(long)jiffies_to_msecs(now - at); } /* if the highest set bit is N, return a mask with bits [N+1, 31] set */ static u32 higher_bits(u32 flags) { return ~((1 << fls(flags)) - 1); } /* return the mask with only the highest bit set */ static u32 highest_bit(u32 flags) { int bit = fls(flags); return ((u64)1 << bit) >> 1; } static bool u32_before(u32 a, u32 b) { return (s32)(a - b) < 0; } #ifdef CONFIG_EXT_SUB_SCHED /** * scx_parent - Find the parent sched * @sch: sched to find the parent of * * Returns the parent scheduler or %NULL if @sch is root. */ static struct scx_sched *scx_parent(struct scx_sched *sch) { if (sch->level) return sch->ancestors[sch->level - 1]; else return NULL; } /** * scx_next_descendant_pre - find the next descendant for pre-order walk * @pos: the current position (%NULL to initiate traversal) * @root: sched whose descendants to walk * * To be used by scx_for_each_descendant_pre(). Find the next descendant to * visit for pre-order traversal of @root's descendants. @root is included in * the iteration and the first node to be visited. */ static struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root) { struct scx_sched *next; lockdep_assert(lockdep_is_held(&scx_enable_mutex) || lockdep_is_held(&scx_sched_lock)); /* if first iteration, visit @root */ if (!pos) return root; /* visit the first child if exists */ next = list_first_entry_or_null(&pos->children, struct scx_sched, sibling); if (next) return next; /* no child, visit my or the closest ancestor's next sibling */ while (pos != root) { if (!list_is_last(&pos->sibling, &scx_parent(pos)->children)) return list_next_entry(pos, sibling); pos = scx_parent(pos); } return NULL; } static struct scx_sched *scx_find_sub_sched(u64 cgroup_id) { return rhashtable_lookup(&scx_sched_hash, &cgroup_id, scx_sched_hash_params); } static void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch) { rcu_assign_pointer(p->scx.sched, sch); } #else /* CONFIG_EXT_SUB_SCHED */ static struct scx_sched *scx_parent(struct scx_sched *sch) { return NULL; } static struct scx_sched *scx_next_descendant_pre(struct scx_sched *pos, struct scx_sched *root) { return pos ? NULL : root; } static struct scx_sched *scx_find_sub_sched(u64 cgroup_id) { return NULL; } static void scx_set_task_sched(struct task_struct *p, struct scx_sched *sch) {} #endif /* CONFIG_EXT_SUB_SCHED */ /** * scx_is_descendant - Test whether sched is a descendant * @sch: sched to test * @ancestor: ancestor sched to test against * * Test whether @sch is a descendant of @ancestor. */ static bool scx_is_descendant(struct scx_sched *sch, struct scx_sched *ancestor) { if (sch->level < ancestor->level) return false; return sch->ancestors[ancestor->level] == ancestor; } /** * scx_for_each_descendant_pre - pre-order walk of a sched's descendants * @pos: iteration cursor * @root: sched to walk the descendants of * * Walk @root's descendants. @root is included in the iteration and the first * node to be visited. Must be called with either scx_enable_mutex or * scx_sched_lock held. */ #define scx_for_each_descendant_pre(pos, root) \ for ((pos) = scx_next_descendant_pre(NULL, (root)); (pos); \ (pos) = scx_next_descendant_pre((pos), (root))) static struct scx_dispatch_q *find_global_dsq(struct scx_sched *sch, s32 cpu) { return &sch->pnode[cpu_to_node(cpu)]->global_dsq; } static struct scx_dispatch_q *find_user_dsq(struct scx_sched *sch, u64 dsq_id) { return rhashtable_lookup(&sch->dsq_hash, &dsq_id, dsq_hash_params); } static const struct sched_class *scx_setscheduler_class(struct task_struct *p) { if (p->sched_class == &stop_sched_class) return &stop_sched_class; return __setscheduler_class(p->policy, p->prio); } static struct scx_dispatch_q *bypass_dsq(struct scx_sched *sch, s32 cpu) { return &per_cpu_ptr(sch->pcpu, cpu)->bypass_dsq; } static struct scx_dispatch_q *bypass_enq_target_dsq(struct scx_sched *sch, s32 cpu) { #ifdef CONFIG_EXT_SUB_SCHED /* * If @sch is a sub-sched which is bypassing, its tasks should go into * the bypass DSQs of the nearest ancestor which is not bypassing. The * not-bypassing ancestor is responsible for scheduling all tasks from * bypassing sub-trees. If all ancestors including root are bypassing, * all tasks should go to the root's bypass DSQs. * * Whenever a sched starts bypassing, all runnable tasks in its subtree * are re-enqueued after scx_bypassing() is turned on, guaranteeing that * all tasks are transferred to the right DSQs. */ while (scx_parent(sch) && scx_bypassing(sch, cpu)) sch = scx_parent(sch); #endif /* CONFIG_EXT_SUB_SCHED */ return bypass_dsq(sch, cpu); } /** * bypass_dsp_enabled - Check if bypass dispatch path is enabled * @sch: scheduler to check * * When a descendant scheduler enters bypass mode, bypassed tasks are scheduled * by the nearest non-bypassing ancestor, or the root scheduler if all ancestors * are bypassing. In the former case, the ancestor is not itself bypassing but * its bypass DSQs will be populated with bypassed tasks from descendants. Thus, * the ancestor's bypass dispatch path must be active even though its own * bypass_depth remains zero. * * This function checks bypass_dsp_enable_depth which is managed separately from * bypass_depth to enable this decoupling. See enable_bypass_dsp() and * disable_bypass_dsp(). */ static bool bypass_dsp_enabled(struct scx_sched *sch) { return unlikely(atomic_read(&sch->bypass_dsp_enable_depth)); } /** * rq_is_open - Is the rq available for immediate execution of an SCX task? * @rq: rq to test * @enq_flags: optional %SCX_ENQ_* of the task being enqueued * * Returns %true if @rq is currently open for executing an SCX task. After a * %false return, @rq is guaranteed to invoke SCX dispatch path at least once * before going to idle and not inserting a task into @rq's local DSQ after a * %false return doesn't cause @rq to stall. */ static bool rq_is_open(struct rq *rq, u64 enq_flags) { lockdep_assert_rq_held(rq); /* * A higher-priority class task is either running or in the process of * waking up on @rq. */ if (sched_class_above(rq->next_class, &ext_sched_class)) return false; /* * @rq is either in transition to or in idle and there is no * higher-priority class task waking up on it. */ if (sched_class_above(&ext_sched_class, rq->next_class)) return true; /* * @rq is either picking, in transition to, or running an SCX task. */ /* * If we're in the dispatch path holding rq lock, $curr may or may not * be ready depending on whether the on-going dispatch decides to extend * $curr's slice. We say yes here and resolve it at the end of dispatch. * See balance_one(). */ if (rq->scx.flags & SCX_RQ_IN_BALANCE) return true; /* * %SCX_ENQ_PREEMPT clears $curr's slice if on SCX and kicks dispatch, * so allow it to avoid spuriously triggering reenq on a combined * PREEMPT|IMMED insertion. */ if (enq_flags & SCX_ENQ_PREEMPT) return true; /* * @rq is either in transition to or running an SCX task and can't go * idle without another SCX dispatch cycle. */ return false; } /* * scx_kf_mask enforcement. Some kfuncs can only be called from specific SCX * ops. When invoking SCX ops, SCX_CALL_OP[_RET]() should be used to indicate * the allowed kfuncs and those kfuncs should use scx_kf_allowed() to check * whether it's running from an allowed context. * * @mask is constant, always inline to cull the mask calculations. */ static __always_inline void scx_kf_allow(u32 mask) { /* nesting is allowed only in increasing scx_kf_mask order */ WARN_ONCE((mask | higher_bits(mask)) & current->scx.kf_mask, "invalid nesting current->scx.kf_mask=0x%x mask=0x%x\n", current->scx.kf_mask, mask); current->scx.kf_mask |= mask; barrier(); } static void scx_kf_disallow(u32 mask) { barrier(); current->scx.kf_mask &= ~mask; } /* * Track the rq currently locked. * * This allows kfuncs to safely operate on rq from any scx ops callback, * knowing which rq is already locked. */ DEFINE_PER_CPU(struct rq *, scx_locked_rq_state); static inline void update_locked_rq(struct rq *rq) { /* * Check whether @rq is actually locked. This can help expose bugs * or incorrect assumptions about the context in which a kfunc or * callback is executed. */ if (rq) lockdep_assert_rq_held(rq); __this_cpu_write(scx_locked_rq_state, rq); } #define SCX_CALL_OP(sch, mask, op, rq, args...) \ do { \ if (rq) \ update_locked_rq(rq); \ if (mask) { \ scx_kf_allow(mask); \ (sch)->ops.op(args); \ scx_kf_disallow(mask); \ } else { \ (sch)->ops.op(args); \ } \ if (rq) \ update_locked_rq(NULL); \ } while (0) #define SCX_CALL_OP_RET(sch, mask, op, rq, args...) \ ({ \ __typeof__((sch)->ops.op(args)) __ret; \ \ if (rq) \ update_locked_rq(rq); \ if (mask) { \ scx_kf_allow(mask); \ __ret = (sch)->ops.op(args); \ scx_kf_disallow(mask); \ } else { \ __ret = (sch)->ops.op(args); \ } \ if (rq) \ update_locked_rq(NULL); \ __ret; \ }) /* * Some kfuncs are allowed only on the tasks that are subjects of the * in-progress scx_ops operation for, e.g., locking guarantees. To enforce such * restrictions, the following SCX_CALL_OP_*() variants should be used when * invoking scx_ops operations that take task arguments. These can only be used * for non-nesting operations due to the way the tasks are tracked. * * kfuncs which can only operate on such tasks can in turn use * scx_kf_allowed_on_arg_tasks() to test whether the invocation is allowed on * the specific task. */ #define SCX_CALL_OP_TASK(sch, mask, op, rq, task, args...) \ do { \ BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL); \ current->scx.kf_tasks[0] = task; \ SCX_CALL_OP((sch), mask, op, rq, task, ##args); \ current->scx.kf_tasks[0] = NULL; \ } while (0) #define SCX_CALL_OP_TASK_RET(sch, mask, op, rq, task, args...) \ ({ \ __typeof__((sch)->ops.op(task, ##args)) __ret; \ BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL); \ current->scx.kf_tasks[0] = task; \ __ret = SCX_CALL_OP_RET((sch), mask, op, rq, task, ##args); \ current->scx.kf_tasks[0] = NULL; \ __ret; \ }) #define SCX_CALL_OP_2TASKS_RET(sch, mask, op, rq, task0, task1, args...) \ ({ \ __typeof__((sch)->ops.op(task0, task1, ##args)) __ret; \ BUILD_BUG_ON((mask) & ~__SCX_KF_TERMINAL); \ current->scx.kf_tasks[0] = task0; \ current->scx.kf_tasks[1] = task1; \ __ret = SCX_CALL_OP_RET((sch), mask, op, rq, task0, task1, ##args); \ current->scx.kf_tasks[0] = NULL; \ current->scx.kf_tasks[1] = NULL; \ __ret; \ }) /* @mask is constant, always inline to cull unnecessary branches */ static __always_inline bool scx_kf_allowed(struct scx_sched *sch, u32 mask) { if (unlikely(!(current->scx.kf_mask & mask))) { scx_error(sch, "kfunc with mask 0x%x called from an operation only allowing 0x%x", mask, current->scx.kf_mask); return false; } /* * Enforce nesting boundaries. e.g. A kfunc which can be called from * DISPATCH must not be called if we're running DEQUEUE which is nested * inside ops.dispatch(). We don't need to check boundaries for any * blocking kfuncs as the verifier ensures they're only called from * sleepable progs. */ if (unlikely(highest_bit(mask) == SCX_KF_CPU_RELEASE && (current->scx.kf_mask & higher_bits(SCX_KF_CPU_RELEASE)))) { scx_error(sch, "cpu_release kfunc called from a nested operation"); return false; } if (unlikely(highest_bit(mask) == SCX_KF_DISPATCH && (current->scx.kf_mask & higher_bits(SCX_KF_DISPATCH)))) { scx_error(sch, "dispatch kfunc called from a nested operation"); return false; } return true; } /* see SCX_CALL_OP_TASK() */ static __always_inline bool scx_kf_allowed_on_arg_tasks(struct scx_sched *sch, u32 mask, struct task_struct *p) { if (!scx_kf_allowed(sch, mask)) return false; if (unlikely((p != current->scx.kf_tasks[0] && p != current->scx.kf_tasks[1]))) { scx_error(sch, "called on a task not being operated on"); return false; } return true; } enum scx_dsq_iter_flags { /* iterate in the reverse dispatch order */ SCX_DSQ_ITER_REV = 1U << 16, __SCX_DSQ_ITER_HAS_SLICE = 1U << 30, __SCX_DSQ_ITER_HAS_VTIME = 1U << 31, __SCX_DSQ_ITER_USER_FLAGS = SCX_DSQ_ITER_REV, __SCX_DSQ_ITER_ALL_FLAGS = __SCX_DSQ_ITER_USER_FLAGS | __SCX_DSQ_ITER_HAS_SLICE | __SCX_DSQ_ITER_HAS_VTIME, }; /** * nldsq_next_task - Iterate to the next task in a non-local DSQ * @dsq: non-local dsq being iterated * @cur: current position, %NULL to start iteration * @rev: walk backwards * * Returns %NULL when iteration is finished. */ static struct task_struct *nldsq_next_task(struct scx_dispatch_q *dsq, struct task_struct *cur, bool rev) { struct list_head *list_node; struct scx_dsq_list_node *dsq_lnode; lockdep_assert_held(&dsq->lock); if (cur) list_node = &cur->scx.dsq_list.node; else list_node = &dsq->list; /* find the next task, need to skip BPF iteration cursors */ do { if (rev) list_node = list_node->prev; else list_node = list_node->next; if (list_node == &dsq->list) return NULL; dsq_lnode = container_of(list_node, struct scx_dsq_list_node, node); } while (dsq_lnode->flags & SCX_DSQ_LNODE_ITER_CURSOR); return container_of(dsq_lnode, struct task_struct, scx.dsq_list); } #define nldsq_for_each_task(p, dsq) \ for ((p) = nldsq_next_task((dsq), NULL, false); (p); \ (p) = nldsq_next_task((dsq), (p), false)) /** * nldsq_cursor_next_task - Iterate to the next task given a cursor in a non-local DSQ * @cursor: scx_dsq_list_node initialized with INIT_DSQ_LIST_CURSOR() * @dsq: non-local dsq being iterated * * Find the next task in a cursor based iteration. The caller must have * initialized @cursor using INIT_DSQ_LIST_CURSOR() and can release the DSQ lock * between the iteration steps. * * Only tasks which were queued before @cursor was initialized are visible. This * bounds the iteration and guarantees that vtime never jumps in the other * direction while iterating. */ static struct task_struct *nldsq_cursor_next_task(struct scx_dsq_list_node *cursor, struct scx_dispatch_q *dsq) { bool rev = cursor->flags & SCX_DSQ_ITER_REV; struct task_struct *p; lockdep_assert_held(&dsq->lock); BUG_ON(!(cursor->flags & SCX_DSQ_LNODE_ITER_CURSOR)); if (list_empty(&cursor->node)) p = NULL; else p = container_of(cursor, struct task_struct, scx.dsq_list); /* skip cursors and tasks that were queued after @cursor init */ do { p = nldsq_next_task(dsq, p, rev); } while (p && unlikely(u32_before(cursor->priv, p->scx.dsq_seq))); if (p) { if (rev) list_move_tail(&cursor->node, &p->scx.dsq_list.node); else list_move(&cursor->node, &p->scx.dsq_list.node); } else { list_del_init(&cursor->node); } return p; } /** * nldsq_cursor_lost_task - Test whether someone else took the task since iteration * @cursor: scx_dsq_list_node initialized with INIT_DSQ_LIST_CURSOR() * @rq: rq @p was on * @dsq: dsq @p was on * @p: target task * * @p is a task returned by nldsq_cursor_next_task(). The locks may have been * dropped and re-acquired inbetween. Verify that no one else took or is in the * process of taking @p from @dsq. * * On %false return, the caller can assume full ownership of @p. */ static bool nldsq_cursor_lost_task(struct scx_dsq_list_node *cursor, struct rq *rq, struct scx_dispatch_q *dsq, struct task_struct *p) { lockdep_assert_rq_held(rq); lockdep_assert_held(&dsq->lock); /* * @p could have already left $src_dsq, got re-enqueud, or be in the * process of being consumed by someone else. */ if (unlikely(p->scx.dsq != dsq || u32_before(cursor->priv, p->scx.dsq_seq) || p->scx.holding_cpu >= 0)) return true; /* if @p has stayed on @dsq, its rq couldn't have changed */ if (WARN_ON_ONCE(rq != task_rq(p))) return true; return false; } /* * BPF DSQ iterator. Tasks in a non-local DSQ can be iterated in [reverse] * dispatch order. BPF-visible iterator is opaque and larger to allow future * changes without breaking backward compatibility. Can be used with * bpf_for_each(). See bpf_iter_scx_dsq_*(). */ struct bpf_iter_scx_dsq_kern { struct scx_dsq_list_node cursor; struct scx_dispatch_q *dsq; u64 slice; u64 vtime; } __attribute__((aligned(8))); struct bpf_iter_scx_dsq { u64 __opaque[6]; } __attribute__((aligned(8))); /* * SCX task iterator. */ struct scx_task_iter { struct sched_ext_entity cursor; struct task_struct *locked_task; struct rq *rq; struct rq_flags rf; u32 cnt; bool list_locked; #ifdef CONFIG_EXT_SUB_SCHED struct cgroup *cgrp; struct cgroup_subsys_state *css_pos; struct css_task_iter css_iter; #endif }; /** * scx_task_iter_start - Lock scx_tasks_lock and start a task iteration * @iter: iterator to init * @cgrp: Optional root of cgroup subhierarchy to iterate * * Initialize @iter. Once initialized, @iter must eventually be stopped with * scx_task_iter_stop(). * * If @cgrp is %NULL, scx_tasks is used for iteration and this function returns * with scx_tasks_lock held and @iter->cursor inserted into scx_tasks. * * If @cgrp is not %NULL, @cgrp and its descendants' tasks are walked using * @iter->css_iter. The caller must be holding cgroup_lock() to prevent cgroup * task migrations. * * The two modes of iterations are largely independent and it's likely that * scx_tasks can be removed in favor of always using cgroup iteration if * CONFIG_SCHED_CLASS_EXT depends on CONFIG_CGROUPS. * * scx_tasks_lock and the rq lock may be released using scx_task_iter_unlock() * between this and the first next() call or between any two next() calls. If * the locks are released between two next() calls, the caller is responsible * for ensuring that the task being iterated remains accessible either through * RCU read lock or obtaining a reference count. * * All tasks which existed when the iteration started are guaranteed to be * visited as long as they are not dead. */ static void scx_task_iter_start(struct scx_task_iter *iter, struct cgroup *cgrp) { memset(iter, 0, sizeof(*iter)); #ifdef CONFIG_EXT_SUB_SCHED if (cgrp) { lockdep_assert_held(&cgroup_mutex); iter->cgrp = cgrp; iter->css_pos = css_next_descendant_pre(NULL, &iter->cgrp->self); css_task_iter_start(iter->css_pos, 0, &iter->css_iter); return; } #endif raw_spin_lock_irq(&scx_tasks_lock); iter->cursor = (struct sched_ext_entity){ .flags = SCX_TASK_CURSOR }; list_add(&iter->cursor.tasks_node, &scx_tasks); iter->list_locked = true; } static void __scx_task_iter_rq_unlock(struct scx_task_iter *iter) { if (iter->locked_task) { __balance_callbacks(iter->rq, &iter->rf); task_rq_unlock(iter->rq, iter->locked_task, &iter->rf); iter->locked_task = NULL; } } /** * scx_task_iter_unlock - Unlock rq and scx_tasks_lock held by a task iterator * @iter: iterator to unlock * * If @iter is in the middle of a locked iteration, it may be locking the rq of * the task currently being visited in addition to scx_tasks_lock. Unlock both. * This function can be safely called anytime during an iteration. The next * iterator operation will automatically restore the necessary locking. */ static void scx_task_iter_unlock(struct scx_task_iter *iter) { __scx_task_iter_rq_unlock(iter); if (iter->list_locked) { iter->list_locked = false; raw_spin_unlock_irq(&scx_tasks_lock); } } static void __scx_task_iter_maybe_relock(struct scx_task_iter *iter) { if (!iter->list_locked) { raw_spin_lock_irq(&scx_tasks_lock); iter->list_locked = true; } } /** * scx_task_iter_stop - Stop a task iteration and unlock scx_tasks_lock * @iter: iterator to exit * * Exit a previously initialized @iter. Must be called with scx_tasks_lock held * which is released on return. If the iterator holds a task's rq lock, that rq * lock is also released. See scx_task_iter_start() for details. */ static void scx_task_iter_stop(struct scx_task_iter *iter) { #ifdef CONFIG_EXT_SUB_SCHED if (iter->cgrp) { if (iter->css_pos) css_task_iter_end(&iter->css_iter); __scx_task_iter_rq_unlock(iter); return; } #endif __scx_task_iter_maybe_relock(iter); list_del_init(&iter->cursor.tasks_node); scx_task_iter_unlock(iter); } /** * scx_task_iter_next - Next task * @iter: iterator to walk * * Visit the next task. See scx_task_iter_start() for details. Locks are dropped * and re-acquired every %SCX_TASK_ITER_BATCH iterations to avoid causing stalls * by holding scx_tasks_lock for too long. */ static struct task_struct *scx_task_iter_next(struct scx_task_iter *iter) { struct list_head *cursor = &iter->cursor.tasks_node; struct sched_ext_entity *pos; if (!(++iter->cnt % SCX_TASK_ITER_BATCH)) { scx_task_iter_unlock(iter); cond_resched(); } #ifdef CONFIG_EXT_SUB_SCHED if (iter->cgrp) { while (iter->css_pos) { struct task_struct *p; p = css_task_iter_next(&iter->css_iter); if (p) return p; css_task_iter_end(&iter->css_iter); iter->css_pos = css_next_descendant_pre(iter->css_pos, &iter->cgrp->self); if (iter->css_pos) css_task_iter_start(iter->css_pos, 0, &iter->css_iter); } return NULL; } #endif __scx_task_iter_maybe_relock(iter); list_for_each_entry(pos, cursor, tasks_node) { if (&pos->tasks_node == &scx_tasks) return NULL; if (!(pos->flags & SCX_TASK_CURSOR)) { list_move(cursor, &pos->tasks_node); return container_of(pos, struct task_struct, scx); } } /* can't happen, should always terminate at scx_tasks above */ BUG(); } /** * scx_task_iter_next_locked - Next non-idle task with its rq locked * @iter: iterator to walk * * Visit the non-idle task with its rq lock held. Allows callers to specify * whether they would like to filter out dead tasks. See scx_task_iter_start() * for details. */ static struct task_struct *scx_task_iter_next_locked(struct scx_task_iter *iter) { struct task_struct *p; __scx_task_iter_rq_unlock(iter); while ((p = scx_task_iter_next(iter))) { /* * scx_task_iter is used to prepare and move tasks into SCX * while loading the BPF scheduler and vice-versa while * unloading. The init_tasks ("swappers") should be excluded * from the iteration because: * * - It's unsafe to use __setschduler_prio() on an init_task to * determine the sched_class to use as it won't preserve its * idle_sched_class. * * - ops.init/exit_task() can easily be confused if called with * init_tasks as they, e.g., share PID 0. * * As init_tasks are never scheduled through SCX, they can be * skipped safely. Note that is_idle_task() which tests %PF_IDLE * doesn't work here: * * - %PF_IDLE may not be set for an init_task whose CPU hasn't * yet been onlined. * * - %PF_IDLE can be set on tasks that are not init_tasks. See * play_idle_precise() used by CONFIG_IDLE_INJECT. * * Test for idle_sched_class as only init_tasks are on it. */ if (p->sched_class != &idle_sched_class) break; } if (!p) return NULL; iter->rq = task_rq_lock(p, &iter->rf); iter->locked_task = p; return p; } /** * scx_add_event - Increase an event counter for 'name' by 'cnt' * @sch: scx_sched to account events for * @name: an event name defined in struct scx_event_stats * @cnt: the number of the event occurred * * This can be used when preemption is not disabled. */ #define scx_add_event(sch, name, cnt) do { \ this_cpu_add((sch)->pcpu->event_stats.name, (cnt)); \ trace_sched_ext_event(#name, (cnt)); \ } while(0) /** * __scx_add_event - Increase an event counter for 'name' by 'cnt' * @sch: scx_sched to account events for * @name: an event name defined in struct scx_event_stats * @cnt: the number of the event occurred * * This should be used only when preemption is disabled. */ #define __scx_add_event(sch, name, cnt) do { \ __this_cpu_add((sch)->pcpu->event_stats.name, (cnt)); \ trace_sched_ext_event(#name, cnt); \ } while(0) /** * scx_agg_event - Aggregate an event counter 'kind' from 'src_e' to 'dst_e' * @dst_e: destination event stats * @src_e: source event stats * @kind: a kind of event to be aggregated */ #define scx_agg_event(dst_e, src_e, kind) do { \ (dst_e)->kind += READ_ONCE((src_e)->kind); \ } while(0) /** * scx_dump_event - Dump an event 'kind' in 'events' to 's' * @s: output seq_buf * @events: event stats * @kind: a kind of event to dump */ #define scx_dump_event(s, events, kind) do { \ dump_line(&(s), "%40s: %16lld", #kind, (events)->kind); \ } while (0) static void scx_read_events(struct scx_sched *sch, struct scx_event_stats *events); static enum scx_enable_state scx_enable_state(void) { return atomic_read(&scx_enable_state_var); } static enum scx_enable_state scx_set_enable_state(enum scx_enable_state to) { return atomic_xchg(&scx_enable_state_var, to); } static bool scx_tryset_enable_state(enum scx_enable_state to, enum scx_enable_state from) { int from_v = from; return atomic_try_cmpxchg(&scx_enable_state_var, &from_v, to); } /** * wait_ops_state - Busy-wait the specified ops state to end * @p: target task * @opss: state to wait the end of * * Busy-wait for @p to transition out of @opss. This can only be used when the * state part of @opss is %SCX_QUEUEING or %SCX_DISPATCHING. This function also * has load_acquire semantics to ensure that the caller can see the updates made * in the enqueueing and dispatching paths. */ static void wait_ops_state(struct task_struct *p, unsigned long opss) { do { cpu_relax(); } while (atomic_long_read_acquire(&p->scx.ops_state) == opss); } static inline bool __cpu_valid(s32 cpu) { return likely(cpu >= 0 && cpu < nr_cpu_ids && cpu_possible(cpu)); } /** * ops_cpu_valid - Verify a cpu number, to be used on ops input args * @sch: scx_sched to abort on error * @cpu: cpu number which came from a BPF ops * @where: extra information reported on error * * @cpu is a cpu number which came from the BPF scheduler and can be any value. * Verify that it is in range and one of the possible cpus. If invalid, trigger * an ops error. */ static bool ops_cpu_valid(struct scx_sched *sch, s32 cpu, const char *where) { if (__cpu_valid(cpu)) { return true; } else { scx_error(sch, "invalid CPU %d%s%s", cpu, where ? " " : "", where ?: ""); return false; } } /** * ops_sanitize_err - Sanitize a -errno value * @sch: scx_sched to error out on error * @ops_name: operation to blame on failure * @err: -errno value to sanitize * * Verify @err is a valid -errno. If not, trigger scx_error() and return * -%EPROTO. This is necessary because returning a rogue -errno up the chain can * cause misbehaviors. For an example, a large negative return from * ops.init_task() triggers an oops when passed up the call chain because the * value fails IS_ERR() test after being encoded with ERR_PTR() and then is * handled as a pointer. */ static int ops_sanitize_err(struct scx_sched *sch, const char *ops_name, s32 err) { if (err < 0 && err >= -MAX_ERRNO) return err; scx_error(sch, "ops.%s() returned an invalid errno %d", ops_name, err); return -EPROTO; } static void deferred_bal_cb_workfn(struct rq *rq) { run_deferred(rq); } static void deferred_irq_workfn(struct irq_work *irq_work) { struct rq *rq = container_of(irq_work, struct rq, scx.deferred_irq_work); raw_spin_rq_lock(rq); run_deferred(rq); raw_spin_rq_unlock(rq); } /** * schedule_deferred - Schedule execution of deferred actions on an rq * @rq: target rq * * Schedule execution of deferred actions on @rq. Deferred actions are executed * with @rq locked but unpinned, and thus can unlock @rq to e.g. migrate tasks * to other rqs. */ static void schedule_deferred(struct rq *rq) { /* * This is the fallback when schedule_deferred_locked() can't use * the cheaper balance callback or wakeup hook paths (the target * CPU is not in balance or wakeup). Currently, this is primarily * hit by reenqueue operations targeting a remote CPU. * * Queue on the target CPU. The deferred work can run from any CPU * correctly - the _locked() path already processes remote rqs from * the calling CPU - but targeting the owning CPU allows IPI delivery * without waiting for the calling CPU to re-enable IRQs and is * cheaper as the reenqueue runs locally. */ irq_work_queue_on(&rq->scx.deferred_irq_work, cpu_of(rq)); } /** * schedule_deferred_locked - Schedule execution of deferred actions on an rq * @rq: target rq * * Schedule execution of deferred actions on @rq. Equivalent to * schedule_deferred() but requires @rq to be locked and can be more efficient. */ static void schedule_deferred_locked(struct rq *rq) { lockdep_assert_rq_held(rq); /* * If in the middle of waking up a task, task_woken_scx() will be called * afterwards which will then run the deferred actions, no need to * schedule anything. */ if (rq->scx.flags & SCX_RQ_IN_WAKEUP) return; /* Don't do anything if there already is a deferred operation. */ if (rq->scx.flags & SCX_RQ_BAL_CB_PENDING) return; /* * If in balance, the balance callbacks will be called before rq lock is * released. Schedule one. * * * We can't directly insert the callback into the * rq's list: The call can drop its lock and make the pending balance * callback visible to unrelated code paths that call rq_pin_lock(). * * Just let balance_one() know that it must do it itself. */ if (rq->scx.flags & SCX_RQ_IN_BALANCE) { rq->scx.flags |= SCX_RQ_BAL_CB_PENDING; return; } /* * No scheduler hooks available. Use the generic irq_work path. The * above WAKEUP and BALANCE paths should cover most of the cases and the * time to IRQ re-enable shouldn't be long. */ schedule_deferred(rq); } static void schedule_dsq_reenq(struct scx_sched *sch, struct scx_dispatch_q *dsq, u64 reenq_flags, struct rq *locked_rq) { struct rq *rq; /* * Allowing reenqueues doesn't make sense while bypassing. This also * blocks from new reenqueues to be scheduled on dead scheds. */ if (unlikely(READ_ONCE(sch->bypass_depth))) return; if (dsq->id == SCX_DSQ_LOCAL) { rq = container_of(dsq, struct rq, scx.local_dsq); struct scx_sched_pcpu *sch_pcpu = per_cpu_ptr(sch->pcpu, cpu_of(rq)); struct scx_deferred_reenq_local *drl = &sch_pcpu->deferred_reenq_local; /* * Pairs with smp_mb() in process_deferred_reenq_locals() and * guarantees that there is a reenq_local() afterwards. */ smp_mb(); if (list_empty(&drl->node) || (READ_ONCE(drl->flags) & reenq_flags) != reenq_flags) { guard(raw_spinlock_irqsave)(&rq->scx.deferred_reenq_lock); if (list_empty(&drl->node)) list_move_tail(&drl->node, &rq->scx.deferred_reenq_locals); WRITE_ONCE(drl->flags, drl->flags | reenq_flags); } } else if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN)) { rq = this_rq(); struct scx_dsq_pcpu *dsq_pcpu = per_cpu_ptr(dsq->pcpu, cpu_of(rq)); struct scx_deferred_reenq_user *dru = &dsq_pcpu->deferred_reenq_user; /* * Pairs with smp_mb() in process_deferred_reenq_users() and * guarantees that there is a reenq_user() afterwards. */ smp_mb(); if (list_empty(&dru->node) || (READ_ONCE(dru->flags) & reenq_flags) != reenq_flags) { guard(raw_spinlock_irqsave)(&rq->scx.deferred_reenq_lock); if (list_empty(&dru->node)) list_move_tail(&dru->node, &rq->scx.deferred_reenq_users); WRITE_ONCE(dru->flags, dru->flags | reenq_flags); } } else { scx_error(sch, "DSQ 0x%llx not allowed for reenq", dsq->id); return; } if (rq == locked_rq) schedule_deferred_locked(rq); else schedule_deferred(rq); } static void schedule_reenq_local(struct rq *rq, u64 reenq_flags) { struct scx_sched *root = rcu_dereference_sched(scx_root); if (WARN_ON_ONCE(!root)) return; schedule_dsq_reenq(root, &rq->scx.local_dsq, reenq_flags, rq); } /** * touch_core_sched - Update timestamp used for core-sched task ordering * @rq: rq to read clock from, must be locked * @p: task to update the timestamp for * * Update @p->scx.core_sched_at timestamp. This is used by scx_prio_less() to * implement global or local-DSQ FIFO ordering for core-sched. Should be called * when a task becomes runnable and its turn on the CPU ends (e.g. slice * exhaustion). */ static void touch_core_sched(struct rq *rq, struct task_struct *p) { lockdep_assert_rq_held(rq); #ifdef CONFIG_SCHED_CORE /* * It's okay to update the timestamp spuriously. Use * sched_core_disabled() which is cheaper than enabled(). * * As this is used to determine ordering between tasks of sibling CPUs, * it may be better to use per-core dispatch sequence instead. */ if (!sched_core_disabled()) p->scx.core_sched_at = sched_clock_cpu(cpu_of(rq)); #endif } /** * touch_core_sched_dispatch - Update core-sched timestamp on dispatch * @rq: rq to read clock from, must be locked * @p: task being dispatched * * If the BPF scheduler implements custom core-sched ordering via * ops.core_sched_before(), @p->scx.core_sched_at is used to implement FIFO * ordering within each local DSQ. This function is called from dispatch paths * and updates @p->scx.core_sched_at if custom core-sched ordering is in effect. */ static void touch_core_sched_dispatch(struct rq *rq, struct task_struct *p) { lockdep_assert_rq_held(rq); #ifdef CONFIG_SCHED_CORE if (unlikely(SCX_HAS_OP(scx_root, core_sched_before))) touch_core_sched(rq, p); #endif } static void update_curr_scx(struct rq *rq) { struct task_struct *curr = rq->curr; s64 delta_exec; delta_exec = update_curr_common(rq); if (unlikely(delta_exec <= 0)) return; if (curr->scx.slice != SCX_SLICE_INF) { curr->scx.slice -= min_t(u64, curr->scx.slice, delta_exec); if (!curr->scx.slice) touch_core_sched(rq, curr); } dl_server_update(&rq->ext_server, delta_exec); } static bool scx_dsq_priq_less(struct rb_node *node_a, const struct rb_node *node_b) { const struct task_struct *a = container_of(node_a, struct task_struct, scx.dsq_priq); const struct task_struct *b = container_of(node_b, struct task_struct, scx.dsq_priq); return time_before64(a->scx.dsq_vtime, b->scx.dsq_vtime); } static void dsq_inc_nr(struct scx_dispatch_q *dsq, struct task_struct *p, u64 enq_flags) { /* scx_bpf_dsq_nr_queued() reads ->nr without locking, use WRITE_ONCE() */ WRITE_ONCE(dsq->nr, dsq->nr + 1); /* * Once @p reaches a local DSQ, it can only leave it by being dispatched * to the CPU or dequeued. In both cases, the only way @p can go back to * the BPF sched is through enqueueing. If being inserted into a local * DSQ with IMMED, persist the state until the next enqueueing event in * do_enqueue_task() so that we can maintain IMMED protection through * e.g. SAVE/RESTORE cycles and slice extensions. */ if (enq_flags & SCX_ENQ_IMMED) { if (unlikely(dsq->id != SCX_DSQ_LOCAL)) { WARN_ON_ONCE(!(enq_flags & SCX_ENQ_GDSQ_FALLBACK)); return; } p->scx.flags |= SCX_TASK_IMMED; } if (p->scx.flags & SCX_TASK_IMMED) { struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); if (WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL)) return; rq->scx.nr_immed++; /* * If @rq already had other tasks or the current task is not * done yet, @p can't go on the CPU immediately. Re-enqueue. */ if (unlikely(dsq->nr > 1 || !rq_is_open(rq, enq_flags))) schedule_reenq_local(rq, 0); } } static void dsq_dec_nr(struct scx_dispatch_q *dsq, struct task_struct *p) { /* see dsq_inc_nr() */ WRITE_ONCE(dsq->nr, dsq->nr - 1); if (p->scx.flags & SCX_TASK_IMMED) { struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); if (WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL) || WARN_ON_ONCE(rq->scx.nr_immed <= 0)) return; rq->scx.nr_immed--; } } static void refill_task_slice_dfl(struct scx_sched *sch, struct task_struct *p) { p->scx.slice = READ_ONCE(sch->slice_dfl); __scx_add_event(sch, SCX_EV_REFILL_SLICE_DFL, 1); } /* * Return true if @p is moving due to an internal SCX migration, false * otherwise. */ static inline bool task_scx_migrating(struct task_struct *p) { /* * We only need to check sticky_cpu: it is set to the destination * CPU in move_remote_task_to_local_dsq() before deactivate_task() * and cleared when the task is enqueued on the destination, so it * is only non-negative during an internal SCX migration. */ return p->scx.sticky_cpu >= 0; } /* * Call ops.dequeue() if the task is in BPF custody and not migrating. * Clears %SCX_TASK_IN_CUSTODY when the callback is invoked. */ static void call_task_dequeue(struct scx_sched *sch, struct rq *rq, struct task_struct *p, u64 deq_flags) { if (!(p->scx.flags & SCX_TASK_IN_CUSTODY) || task_scx_migrating(p)) return; if (SCX_HAS_OP(sch, dequeue)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, dequeue, rq, p, deq_flags); p->scx.flags &= ~SCX_TASK_IN_CUSTODY; } static void local_dsq_post_enq(struct scx_dispatch_q *dsq, struct task_struct *p, u64 enq_flags) { struct rq *rq = container_of(dsq, struct rq, scx.local_dsq); bool preempt = false; call_task_dequeue(scx_root, rq, p, 0); /* * If @rq is in balance, the CPU is already vacant and looking for the * next task to run. No need to preempt or trigger resched after moving * @p into its local DSQ. */ if (rq->scx.flags & SCX_RQ_IN_BALANCE) return; if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr && rq->curr->sched_class == &ext_sched_class) { rq->curr->scx.slice = 0; preempt = true; } if (preempt || sched_class_above(&ext_sched_class, rq->curr->sched_class)) resched_curr(rq); } static void dispatch_enqueue(struct scx_sched *sch, struct rq *rq, struct scx_dispatch_q *dsq, struct task_struct *p, u64 enq_flags) { bool is_local = dsq->id == SCX_DSQ_LOCAL; WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node)); WARN_ON_ONCE((p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) || !RB_EMPTY_NODE(&p->scx.dsq_priq)); if (!is_local) { raw_spin_lock_nested(&dsq->lock, (enq_flags & SCX_ENQ_NESTED) ? SINGLE_DEPTH_NESTING : 0); if (unlikely(dsq->id == SCX_DSQ_INVALID)) { scx_error(sch, "attempting to dispatch to a destroyed dsq"); /* fall back to the global dsq */ raw_spin_unlock(&dsq->lock); dsq = find_global_dsq(sch, task_cpu(p)); raw_spin_lock(&dsq->lock); } } if (unlikely((dsq->id & SCX_DSQ_FLAG_BUILTIN) && (enq_flags & SCX_ENQ_DSQ_PRIQ))) { /* * SCX_DSQ_LOCAL and SCX_DSQ_GLOBAL DSQs always consume from * their FIFO queues. To avoid confusion and accidentally * starving vtime-dispatched tasks by FIFO-dispatched tasks, we * disallow any internal DSQ from doing vtime ordering of * tasks. */ scx_error(sch, "cannot use vtime ordering for built-in DSQs"); enq_flags &= ~SCX_ENQ_DSQ_PRIQ; } if (enq_flags & SCX_ENQ_DSQ_PRIQ) { struct rb_node *rbp; /* * A PRIQ DSQ shouldn't be using FIFO enqueueing. As tasks are * linked to both the rbtree and list on PRIQs, this can only be * tested easily when adding the first task. */ if (unlikely(RB_EMPTY_ROOT(&dsq->priq) && nldsq_next_task(dsq, NULL, false))) scx_error(sch, "DSQ ID 0x%016llx already had FIFO-enqueued tasks", dsq->id); p->scx.dsq_flags |= SCX_TASK_DSQ_ON_PRIQ; rb_add(&p->scx.dsq_priq, &dsq->priq, scx_dsq_priq_less); /* * Find the previous task and insert after it on the list so * that @dsq->list is vtime ordered. */ rbp = rb_prev(&p->scx.dsq_priq); if (rbp) { struct task_struct *prev = container_of(rbp, struct task_struct, scx.dsq_priq); list_add(&p->scx.dsq_list.node, &prev->scx.dsq_list.node); /* first task unchanged - no update needed */ } else { list_add(&p->scx.dsq_list.node, &dsq->list); /* not builtin and new task is at head - use fastpath */ rcu_assign_pointer(dsq->first_task, p); } } else { /* a FIFO DSQ shouldn't be using PRIQ enqueuing */ if (unlikely(!RB_EMPTY_ROOT(&dsq->priq))) scx_error(sch, "DSQ ID 0x%016llx already had PRIQ-enqueued tasks", dsq->id); if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) { list_add(&p->scx.dsq_list.node, &dsq->list); /* new task inserted at head - use fastpath */ if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN)) rcu_assign_pointer(dsq->first_task, p); } else { bool was_empty; was_empty = list_empty(&dsq->list); list_add_tail(&p->scx.dsq_list.node, &dsq->list); if (was_empty && !(dsq->id & SCX_DSQ_FLAG_BUILTIN)) rcu_assign_pointer(dsq->first_task, p); } } /* seq records the order tasks are queued, used by BPF DSQ iterator */ WRITE_ONCE(dsq->seq, dsq->seq + 1); p->scx.dsq_seq = dsq->seq; dsq_inc_nr(dsq, p, enq_flags); p->scx.dsq = dsq; /* * scx.ddsp_dsq_id and scx.ddsp_enq_flags are only relevant on the * direct dispatch path, but we clear them here because the direct * dispatch verdict may be overridden on the enqueue path during e.g. * bypass. */ p->scx.ddsp_dsq_id = SCX_DSQ_INVALID; p->scx.ddsp_enq_flags = 0; /* * Update custody and call ops.dequeue() before clearing ops_state: * once ops_state is cleared, waiters in ops_dequeue() can proceed * and dequeue_task_scx() will RMW p->scx.flags. If we clear * ops_state first, both sides would modify p->scx.flags * concurrently in a non-atomic way. */ if (is_local) { local_dsq_post_enq(dsq, p, enq_flags); } else { /* * Task on global/bypass DSQ: leave custody, task on * non-terminal DSQ: enter custody. */ if (dsq->id == SCX_DSQ_GLOBAL || dsq->id == SCX_DSQ_BYPASS) call_task_dequeue(sch, rq, p, 0); else p->scx.flags |= SCX_TASK_IN_CUSTODY; raw_spin_unlock(&dsq->lock); } /* * We're transitioning out of QUEUEING or DISPATCHING. store_release to * match waiters' load_acquire. */ if (enq_flags & SCX_ENQ_CLEAR_OPSS) atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); } static void task_unlink_from_dsq(struct task_struct *p, struct scx_dispatch_q *dsq) { WARN_ON_ONCE(list_empty(&p->scx.dsq_list.node)); if (p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) { rb_erase(&p->scx.dsq_priq, &dsq->priq); RB_CLEAR_NODE(&p->scx.dsq_priq); p->scx.dsq_flags &= ~SCX_TASK_DSQ_ON_PRIQ; } list_del_init(&p->scx.dsq_list.node); dsq_dec_nr(dsq, p); if (!(dsq->id & SCX_DSQ_FLAG_BUILTIN) && dsq->first_task == p) { struct task_struct *first_task; first_task = nldsq_next_task(dsq, NULL, false); rcu_assign_pointer(dsq->first_task, first_task); } } static void dispatch_dequeue(struct rq *rq, struct task_struct *p) { struct scx_dispatch_q *dsq = p->scx.dsq; bool is_local = dsq == &rq->scx.local_dsq; lockdep_assert_rq_held(rq); if (!dsq) { /* * If !dsq && on-list, @p is on @rq's ddsp_deferred_locals. * Unlinking is all that's needed to cancel. */ if (unlikely(!list_empty(&p->scx.dsq_list.node))) list_del_init(&p->scx.dsq_list.node); /* * When dispatching directly from the BPF scheduler to a local * DSQ, the task isn't associated with any DSQ but * @p->scx.holding_cpu may be set under the protection of * %SCX_OPSS_DISPATCHING. */ if (p->scx.holding_cpu >= 0) p->scx.holding_cpu = -1; return; } if (!is_local) raw_spin_lock(&dsq->lock); /* * Now that we hold @dsq->lock, @p->holding_cpu and @p->scx.dsq_* can't * change underneath us. */ if (p->scx.holding_cpu < 0) { /* @p must still be on @dsq, dequeue */ task_unlink_from_dsq(p, dsq); } else { /* * We're racing against dispatch_to_local_dsq() which already * removed @p from @dsq and set @p->scx.holding_cpu. Clear the * holding_cpu which tells dispatch_to_local_dsq() that it lost * the race. */ WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node)); p->scx.holding_cpu = -1; } p->scx.dsq = NULL; if (!is_local) raw_spin_unlock(&dsq->lock); } /* * Abbreviated version of dispatch_dequeue() that can be used when both @p's rq * and dsq are locked. */ static void dispatch_dequeue_locked(struct task_struct *p, struct scx_dispatch_q *dsq) { lockdep_assert_rq_held(task_rq(p)); lockdep_assert_held(&dsq->lock); task_unlink_from_dsq(p, dsq); p->scx.dsq = NULL; } static struct scx_dispatch_q *find_dsq_for_dispatch(struct scx_sched *sch, struct rq *rq, u64 dsq_id, s32 tcpu) { struct scx_dispatch_q *dsq; if (dsq_id == SCX_DSQ_LOCAL) return &rq->scx.local_dsq; if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) { s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK; if (!ops_cpu_valid(sch, cpu, "in SCX_DSQ_LOCAL_ON dispatch verdict")) return find_global_dsq(sch, tcpu); return &cpu_rq(cpu)->scx.local_dsq; } if (dsq_id == SCX_DSQ_GLOBAL) dsq = find_global_dsq(sch, tcpu); else dsq = find_user_dsq(sch, dsq_id); if (unlikely(!dsq)) { scx_error(sch, "non-existent DSQ 0x%llx", dsq_id); return find_global_dsq(sch, tcpu); } return dsq; } static void mark_direct_dispatch(struct scx_sched *sch, struct task_struct *ddsp_task, struct task_struct *p, u64 dsq_id, u64 enq_flags) { /* * Mark that dispatch already happened from ops.select_cpu() or * ops.enqueue() by spoiling direct_dispatch_task with a non-NULL value * which can never match a valid task pointer. */ __this_cpu_write(direct_dispatch_task, ERR_PTR(-ESRCH)); /* @p must match the task on the enqueue path */ if (unlikely(p != ddsp_task)) { if (IS_ERR(ddsp_task)) scx_error(sch, "%s[%d] already direct-dispatched", p->comm, p->pid); else scx_error(sch, "scheduling for %s[%d] but trying to direct-dispatch %s[%d]", ddsp_task->comm, ddsp_task->pid, p->comm, p->pid); return; } WARN_ON_ONCE(p->scx.ddsp_dsq_id != SCX_DSQ_INVALID); WARN_ON_ONCE(p->scx.ddsp_enq_flags); p->scx.ddsp_dsq_id = dsq_id; p->scx.ddsp_enq_flags = enq_flags; } static void direct_dispatch(struct scx_sched *sch, struct task_struct *p, u64 enq_flags) { struct rq *rq = task_rq(p); struct scx_dispatch_q *dsq = find_dsq_for_dispatch(sch, rq, p->scx.ddsp_dsq_id, task_cpu(p)); touch_core_sched_dispatch(rq, p); p->scx.ddsp_enq_flags |= enq_flags; /* * We are in the enqueue path with @rq locked and pinned, and thus can't * double lock a remote rq and enqueue to its local DSQ. For * DSQ_LOCAL_ON verdicts targeting the local DSQ of a remote CPU, defer * the enqueue so that it's executed when @rq can be unlocked. */ if (dsq->id == SCX_DSQ_LOCAL && dsq != &rq->scx.local_dsq) { unsigned long opss; opss = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_STATE_MASK; switch (opss & SCX_OPSS_STATE_MASK) { case SCX_OPSS_NONE: break; case SCX_OPSS_QUEUEING: /* * As @p was never passed to the BPF side, _release is * not strictly necessary. Still do it for consistency. */ atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); break; default: WARN_ONCE(true, "sched_ext: %s[%d] has invalid ops state 0x%lx in direct_dispatch()", p->comm, p->pid, opss); atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); break; } WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node)); list_add_tail(&p->scx.dsq_list.node, &rq->scx.ddsp_deferred_locals); schedule_deferred_locked(rq); return; } dispatch_enqueue(sch, rq, dsq, p, p->scx.ddsp_enq_flags | SCX_ENQ_CLEAR_OPSS); } static bool scx_rq_online(struct rq *rq) { /* * Test both cpu_active() and %SCX_RQ_ONLINE. %SCX_RQ_ONLINE indicates * the online state as seen from the BPF scheduler. cpu_active() test * guarantees that, if this function returns %true, %SCX_RQ_ONLINE will * stay set until the current scheduling operation is complete even if * we aren't locking @rq. */ return likely((rq->scx.flags & SCX_RQ_ONLINE) && cpu_active(cpu_of(rq))); } static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags, int sticky_cpu) { struct scx_sched *sch = scx_task_sched(p); struct task_struct **ddsp_taskp; struct scx_dispatch_q *dsq; unsigned long qseq; WARN_ON_ONCE(!(p->scx.flags & SCX_TASK_QUEUED)); /* internal movements - rq migration / RESTORE */ if (sticky_cpu == cpu_of(rq)) goto local_norefill; /* * Clear persistent TASK_IMMED for fresh enqueues, see dsq_inc_nr(). * Note that exiting and migration-disabled tasks that skip * ops.enqueue() below will lose IMMED protection unless * %SCX_OPS_ENQ_EXITING / %SCX_OPS_ENQ_MIGRATION_DISABLED are set. */ p->scx.flags &= ~SCX_TASK_IMMED; /* * If !scx_rq_online(), we already told the BPF scheduler that the CPU * is offline and are just running the hotplug path. Don't bother the * BPF scheduler. */ if (!scx_rq_online(rq)) goto local; if (scx_bypassing(sch, cpu_of(rq))) { __scx_add_event(sch, SCX_EV_BYPASS_DISPATCH, 1); goto bypass; } if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID) goto direct; /* see %SCX_OPS_ENQ_EXITING */ if (!(sch->ops.flags & SCX_OPS_ENQ_EXITING) && unlikely(p->flags & PF_EXITING)) { __scx_add_event(sch, SCX_EV_ENQ_SKIP_EXITING, 1); goto local; } /* see %SCX_OPS_ENQ_MIGRATION_DISABLED */ if (!(sch->ops.flags & SCX_OPS_ENQ_MIGRATION_DISABLED) && is_migration_disabled(p)) { __scx_add_event(sch, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED, 1); goto local; } if (unlikely(!SCX_HAS_OP(sch, enqueue))) goto global; /* DSQ bypass didn't trigger, enqueue on the BPF scheduler */ qseq = rq->scx.ops_qseq++ << SCX_OPSS_QSEQ_SHIFT; WARN_ON_ONCE(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE); atomic_long_set(&p->scx.ops_state, SCX_OPSS_QUEUEING | qseq); ddsp_taskp = this_cpu_ptr(&direct_dispatch_task); WARN_ON_ONCE(*ddsp_taskp); *ddsp_taskp = p; SCX_CALL_OP_TASK(sch, SCX_KF_ENQUEUE, enqueue, rq, p, enq_flags); *ddsp_taskp = NULL; if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID) goto direct; /* * Task is now in BPF scheduler's custody. Set %SCX_TASK_IN_CUSTODY * so ops.dequeue() is called when it leaves custody. */ p->scx.flags |= SCX_TASK_IN_CUSTODY; /* * If not directly dispatched, QUEUEING isn't clear yet and dispatch or * dequeue may be waiting. The store_release matches their load_acquire. */ atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_QUEUED | qseq); return; direct: direct_dispatch(sch, p, enq_flags); return; local_norefill: dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, enq_flags); return; local: dsq = &rq->scx.local_dsq; goto enqueue; global: dsq = find_global_dsq(sch, task_cpu(p)); goto enqueue; bypass: dsq = bypass_enq_target_dsq(sch, task_cpu(p)); goto enqueue; enqueue: /* * For task-ordering, slice refill must be treated as implying the end * of the current slice. Otherwise, the longer @p stays on the CPU, the * higher priority it becomes from scx_prio_less()'s POV. */ touch_core_sched(rq, p); refill_task_slice_dfl(sch, p); dispatch_enqueue(sch, rq, dsq, p, enq_flags); } static bool task_runnable(const struct task_struct *p) { return !list_empty(&p->scx.runnable_node); } static void set_task_runnable(struct rq *rq, struct task_struct *p) { lockdep_assert_rq_held(rq); if (p->scx.flags & SCX_TASK_RESET_RUNNABLE_AT) { p->scx.runnable_at = jiffies; p->scx.flags &= ~SCX_TASK_RESET_RUNNABLE_AT; } /* * list_add_tail() must be used. scx_bypass() depends on tasks being * appended to the runnable_list. */ list_add_tail(&p->scx.runnable_node, &rq->scx.runnable_list); } static void clr_task_runnable(struct task_struct *p, bool reset_runnable_at) { list_del_init(&p->scx.runnable_node); if (reset_runnable_at) p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; } static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int core_enq_flags) { struct scx_sched *sch = scx_task_sched(p); int sticky_cpu = p->scx.sticky_cpu; u64 enq_flags = core_enq_flags | rq->scx.extra_enq_flags; if (enq_flags & ENQUEUE_WAKEUP) rq->scx.flags |= SCX_RQ_IN_WAKEUP; /* * Restoring a running task will be immediately followed by * set_next_task_scx() which expects the task to not be on the BPF * scheduler as tasks can only start running through local DSQs. Force * direct-dispatch into the local DSQ by setting the sticky_cpu. */ if (unlikely(enq_flags & ENQUEUE_RESTORE) && task_current(rq, p)) sticky_cpu = cpu_of(rq); if (p->scx.flags & SCX_TASK_QUEUED) { WARN_ON_ONCE(!task_runnable(p)); goto out; } set_task_runnable(rq, p); p->scx.flags |= SCX_TASK_QUEUED; rq->scx.nr_running++; add_nr_running(rq, 1); if (SCX_HAS_OP(sch, runnable) && !task_on_rq_migrating(p)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, runnable, rq, p, enq_flags); if (enq_flags & SCX_ENQ_WAKEUP) touch_core_sched(rq, p); /* Start dl_server if this is the first task being enqueued */ if (rq->scx.nr_running == 1) dl_server_start(&rq->ext_server); do_enqueue_task(rq, p, enq_flags, sticky_cpu); if (sticky_cpu >= 0) p->scx.sticky_cpu = -1; out: rq->scx.flags &= ~SCX_RQ_IN_WAKEUP; if ((enq_flags & SCX_ENQ_CPU_SELECTED) && unlikely(cpu_of(rq) != p->scx.selected_cpu)) __scx_add_event(sch, SCX_EV_SELECT_CPU_FALLBACK, 1); } static void ops_dequeue(struct rq *rq, struct task_struct *p, u64 deq_flags) { struct scx_sched *sch = scx_task_sched(p); unsigned long opss; /* dequeue is always temporary, don't reset runnable_at */ clr_task_runnable(p, false); /* acquire ensures that we see the preceding updates on QUEUED */ opss = atomic_long_read_acquire(&p->scx.ops_state); switch (opss & SCX_OPSS_STATE_MASK) { case SCX_OPSS_NONE: break; case SCX_OPSS_QUEUEING: /* * QUEUEING is started and finished while holding @p's rq lock. * As we're holding the rq lock now, we shouldn't see QUEUEING. */ BUG(); case SCX_OPSS_QUEUED: /* A queued task must always be in BPF scheduler's custody */ WARN_ON_ONCE(!(p->scx.flags & SCX_TASK_IN_CUSTODY)); if (atomic_long_try_cmpxchg(&p->scx.ops_state, &opss, SCX_OPSS_NONE)) break; fallthrough; case SCX_OPSS_DISPATCHING: /* * If @p is being dispatched from the BPF scheduler to a DSQ, * wait for the transfer to complete so that @p doesn't get * added to its DSQ after dequeueing is complete. * * As we're waiting on DISPATCHING with the rq locked, the * dispatching side shouldn't try to lock the rq while * DISPATCHING is set. See dispatch_to_local_dsq(). * * DISPATCHING shouldn't have qseq set and control can reach * here with NONE @opss from the above QUEUED case block. * Explicitly wait on %SCX_OPSS_DISPATCHING instead of @opss. */ wait_ops_state(p, SCX_OPSS_DISPATCHING); BUG_ON(atomic_long_read(&p->scx.ops_state) != SCX_OPSS_NONE); break; } /* * Call ops.dequeue() if the task is still in BPF custody. * * The code that clears ops_state to %SCX_OPSS_NONE does not always * clear %SCX_TASK_IN_CUSTODY: in dispatch_to_local_dsq(), when * we're moving a task that was in %SCX_OPSS_DISPATCHING to a * remote CPU's local DSQ, we only set ops_state to %SCX_OPSS_NONE * so that a concurrent dequeue can proceed, but we clear * %SCX_TASK_IN_CUSTODY only when we later enqueue or move the * task. So we can see NONE + IN_CUSTODY here and we must handle * it. Similarly, after waiting on %SCX_OPSS_DISPATCHING we see * NONE but the task may still have %SCX_TASK_IN_CUSTODY set until * it is enqueued on the destination. */ call_task_dequeue(sch, rq, p, deq_flags); } static bool dequeue_task_scx(struct rq *rq, struct task_struct *p, int core_deq_flags) { struct scx_sched *sch = scx_task_sched(p); u64 deq_flags = core_deq_flags; /* * Set %SCX_DEQ_SCHED_CHANGE when the dequeue is due to a property * change (not sleep or core-sched pick). */ if (!(deq_flags & (DEQUEUE_SLEEP | SCX_DEQ_CORE_SCHED_EXEC))) deq_flags |= SCX_DEQ_SCHED_CHANGE; if (!(p->scx.flags & SCX_TASK_QUEUED)) { WARN_ON_ONCE(task_runnable(p)); return true; } ops_dequeue(rq, p, deq_flags); /* * A currently running task which is going off @rq first gets dequeued * and then stops running. As we want running <-> stopping transitions * to be contained within runnable <-> quiescent transitions, trigger * ->stopping() early here instead of in put_prev_task_scx(). * * @p may go through multiple stopping <-> running transitions between * here and put_prev_task_scx() if task attribute changes occur while * balance_one() leaves @rq unlocked. However, they don't contain any * information meaningful to the BPF scheduler and can be suppressed by * skipping the callbacks if the task is !QUEUED. */ if (SCX_HAS_OP(sch, stopping) && task_current(rq, p)) { update_curr_scx(rq); SCX_CALL_OP_TASK(sch, SCX_KF_REST, stopping, rq, p, false); } if (SCX_HAS_OP(sch, quiescent) && !task_on_rq_migrating(p)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, quiescent, rq, p, deq_flags); if (deq_flags & SCX_DEQ_SLEEP) p->scx.flags |= SCX_TASK_DEQD_FOR_SLEEP; else p->scx.flags &= ~SCX_TASK_DEQD_FOR_SLEEP; p->scx.flags &= ~SCX_TASK_QUEUED; rq->scx.nr_running--; sub_nr_running(rq, 1); dispatch_dequeue(rq, p); return true; } static void yield_task_scx(struct rq *rq) { struct task_struct *p = rq->donor; struct scx_sched *sch = scx_task_sched(p); if (SCX_HAS_OP(sch, yield)) SCX_CALL_OP_2TASKS_RET(sch, SCX_KF_REST, yield, rq, p, NULL); else p->scx.slice = 0; } static bool yield_to_task_scx(struct rq *rq, struct task_struct *to) { struct task_struct *from = rq->donor; struct scx_sched *sch = scx_task_sched(from); if (SCX_HAS_OP(sch, yield) && sch == scx_task_sched(to)) return SCX_CALL_OP_2TASKS_RET(sch, SCX_KF_REST, yield, rq, from, to); else return false; } static void wakeup_preempt_scx(struct rq *rq, struct task_struct *p, int wake_flags) { /* * Preemption between SCX tasks is implemented by resetting the victim * task's slice to 0 and triggering reschedule on the target CPU. * Nothing to do. */ if (p->sched_class == &ext_sched_class) return; /* * Getting preempted by a higher-priority class. Reenqueue IMMED tasks. * This captures all preemption cases including: * * - A SCX task is currently running. * * - @rq is waking from idle due to a SCX task waking to it. * * - A higher-priority wakes up while SCX dispatch is in progress. */ if (rq->scx.nr_immed) schedule_reenq_local(rq, 0); } static void move_local_task_to_local_dsq(struct task_struct *p, u64 enq_flags, struct scx_dispatch_q *src_dsq, struct rq *dst_rq) { struct scx_dispatch_q *dst_dsq = &dst_rq->scx.local_dsq; /* @dsq is locked and @p is on @dst_rq */ lockdep_assert_held(&src_dsq->lock); lockdep_assert_rq_held(dst_rq); WARN_ON_ONCE(p->scx.holding_cpu >= 0); if (enq_flags & (SCX_ENQ_HEAD | SCX_ENQ_PREEMPT)) list_add(&p->scx.dsq_list.node, &dst_dsq->list); else list_add_tail(&p->scx.dsq_list.node, &dst_dsq->list); dsq_inc_nr(dst_dsq, p, enq_flags); p->scx.dsq = dst_dsq; local_dsq_post_enq(dst_dsq, p, enq_flags); } /** * move_remote_task_to_local_dsq - Move a task from a foreign rq to a local DSQ * @p: task to move * @enq_flags: %SCX_ENQ_* * @src_rq: rq to move the task from, locked on entry, released on return * @dst_rq: rq to move the task into, locked on return * * Move @p which is currently on @src_rq to @dst_rq's local DSQ. */ static void move_remote_task_to_local_dsq(struct task_struct *p, u64 enq_flags, struct rq *src_rq, struct rq *dst_rq) { lockdep_assert_rq_held(src_rq); /* * Set sticky_cpu before deactivate_task() to properly mark the * beginning of an SCX-internal migration. */ p->scx.sticky_cpu = cpu_of(dst_rq); deactivate_task(src_rq, p, 0); set_task_cpu(p, cpu_of(dst_rq)); raw_spin_rq_unlock(src_rq); raw_spin_rq_lock(dst_rq); /* * We want to pass scx-specific enq_flags but activate_task() will * truncate the upper 32 bit. As we own @rq, we can pass them through * @rq->scx.extra_enq_flags instead. */ WARN_ON_ONCE(!cpumask_test_cpu(cpu_of(dst_rq), p->cpus_ptr)); WARN_ON_ONCE(dst_rq->scx.extra_enq_flags); dst_rq->scx.extra_enq_flags = enq_flags; activate_task(dst_rq, p, 0); dst_rq->scx.extra_enq_flags = 0; } /* * Similar to kernel/sched/core.c::is_cpu_allowed(). However, there are two * differences: * * - is_cpu_allowed() asks "Can this task run on this CPU?" while * task_can_run_on_remote_rq() asks "Can the BPF scheduler migrate the task to * this CPU?". * * While migration is disabled, is_cpu_allowed() has to say "yes" as the task * must be allowed to finish on the CPU that it's currently on regardless of * the CPU state. However, task_can_run_on_remote_rq() must say "no" as the * BPF scheduler shouldn't attempt to migrate a task which has migration * disabled. * * - The BPF scheduler is bypassed while the rq is offline and we can always say * no to the BPF scheduler initiated migrations while offline. * * The caller must ensure that @p and @rq are on different CPUs. */ static bool task_can_run_on_remote_rq(struct scx_sched *sch, struct task_struct *p, struct rq *rq, bool enforce) { s32 cpu = cpu_of(rq); WARN_ON_ONCE(task_cpu(p) == cpu); /* * If @p has migration disabled, @p->cpus_ptr is updated to contain only * the pinned CPU in migrate_disable_switch() while @p is being switched * out. However, put_prev_task_scx() is called before @p->cpus_ptr is * updated and thus another CPU may see @p on a DSQ inbetween leading to * @p passing the below task_allowed_on_cpu() check while migration is * disabled. * * Test the migration disabled state first as the race window is narrow * and the BPF scheduler failing to check migration disabled state can * easily be masked if task_allowed_on_cpu() is done first. */ if (unlikely(is_migration_disabled(p))) { if (enforce) scx_error(sch, "SCX_DSQ_LOCAL[_ON] cannot move migration disabled %s[%d] from CPU %d to %d", p->comm, p->pid, task_cpu(p), cpu); return false; } /* * We don't require the BPF scheduler to avoid dispatching to offline * CPUs mostly for convenience but also because CPUs can go offline * between scx_bpf_dsq_insert() calls and here. Trigger error iff the * picked CPU is outside the allowed mask. */ if (!task_allowed_on_cpu(p, cpu)) { if (enforce) scx_error(sch, "SCX_DSQ_LOCAL[_ON] target CPU %d not allowed for %s[%d]", cpu, p->comm, p->pid); return false; } if (!scx_rq_online(rq)) { if (enforce) __scx_add_event(sch, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE, 1); return false; } return true; } /** * unlink_dsq_and_lock_src_rq() - Unlink task from its DSQ and lock its task_rq * @p: target task * @dsq: locked DSQ @p is currently on * @src_rq: rq @p is currently on, stable with @dsq locked * * Called with @dsq locked but no rq's locked. We want to move @p to a different * DSQ, including any local DSQ, but are not locking @src_rq. Locking @src_rq is * required when transferring into a local DSQ. Even when transferring into a * non-local DSQ, it's better to use the same mechanism to protect against * dequeues and maintain the invariant that @p->scx.dsq can only change while * @src_rq is locked, which e.g. scx_dump_task() depends on. * * We want to grab @src_rq but that can deadlock if we try while locking @dsq, * so we want to unlink @p from @dsq, drop its lock and then lock @src_rq. As * this may race with dequeue, which can't drop the rq lock or fail, do a little * dancing from our side. * * @p->scx.holding_cpu is set to this CPU before @dsq is unlocked. If @p gets * dequeued after we unlock @dsq but before locking @src_rq, the holding_cpu * would be cleared to -1. While other cpus may have updated it to different * values afterwards, as this operation can't be preempted or recurse, the * holding_cpu can never become this CPU again before we're done. Thus, we can * tell whether we lost to dequeue by testing whether the holding_cpu still * points to this CPU. See dispatch_dequeue() for the counterpart. * * On return, @dsq is unlocked and @src_rq is locked. Returns %true if @p is * still valid. %false if lost to dequeue. */ static bool unlink_dsq_and_lock_src_rq(struct task_struct *p, struct scx_dispatch_q *dsq, struct rq *src_rq) { s32 cpu = raw_smp_processor_id(); lockdep_assert_held(&dsq->lock); WARN_ON_ONCE(p->scx.holding_cpu >= 0); task_unlink_from_dsq(p, dsq); p->scx.holding_cpu = cpu; raw_spin_unlock(&dsq->lock); raw_spin_rq_lock(src_rq); /* task_rq couldn't have changed if we're still the holding cpu */ return likely(p->scx.holding_cpu == cpu) && !WARN_ON_ONCE(src_rq != task_rq(p)); } static bool consume_remote_task(struct rq *this_rq, struct task_struct *p, u64 enq_flags, struct scx_dispatch_q *dsq, struct rq *src_rq) { raw_spin_rq_unlock(this_rq); if (unlink_dsq_and_lock_src_rq(p, dsq, src_rq)) { move_remote_task_to_local_dsq(p, enq_flags, src_rq, this_rq); return true; } else { raw_spin_rq_unlock(src_rq); raw_spin_rq_lock(this_rq); return false; } } /** * move_task_between_dsqs() - Move a task from one DSQ to another * @sch: scx_sched being operated on * @p: target task * @enq_flags: %SCX_ENQ_* * @src_dsq: DSQ @p is currently on, must not be a local DSQ * @dst_dsq: DSQ @p is being moved to, can be any DSQ * * Must be called with @p's task_rq and @src_dsq locked. If @dst_dsq is a local * DSQ and @p is on a different CPU, @p will be migrated and thus its task_rq * will change. As @p's task_rq is locked, this function doesn't need to use the * holding_cpu mechanism. * * On return, @src_dsq is unlocked and only @p's new task_rq, which is the * return value, is locked. */ static struct rq *move_task_between_dsqs(struct scx_sched *sch, struct task_struct *p, u64 enq_flags, struct scx_dispatch_q *src_dsq, struct scx_dispatch_q *dst_dsq) { struct rq *src_rq = task_rq(p), *dst_rq; BUG_ON(src_dsq->id == SCX_DSQ_LOCAL); lockdep_assert_held(&src_dsq->lock); lockdep_assert_rq_held(src_rq); if (dst_dsq->id == SCX_DSQ_LOCAL) { dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); if (src_rq != dst_rq && unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) { dst_dsq = find_global_dsq(sch, task_cpu(p)); dst_rq = src_rq; enq_flags |= SCX_ENQ_GDSQ_FALLBACK; } } else { /* no need to migrate if destination is a non-local DSQ */ dst_rq = src_rq; } /* * Move @p into $dst_dsq. If $dst_dsq is the local DSQ of a different * CPU, @p will be migrated. */ if (dst_dsq->id == SCX_DSQ_LOCAL) { /* @p is going from a non-local DSQ to a local DSQ */ if (src_rq == dst_rq) { task_unlink_from_dsq(p, src_dsq); move_local_task_to_local_dsq(p, enq_flags, src_dsq, dst_rq); raw_spin_unlock(&src_dsq->lock); } else { raw_spin_unlock(&src_dsq->lock); move_remote_task_to_local_dsq(p, enq_flags, src_rq, dst_rq); } } else { /* * @p is going from a non-local DSQ to a non-local DSQ. As * $src_dsq is already locked, do an abbreviated dequeue. */ dispatch_dequeue_locked(p, src_dsq); raw_spin_unlock(&src_dsq->lock); dispatch_enqueue(sch, dst_rq, dst_dsq, p, enq_flags); } return dst_rq; } static bool consume_dispatch_q(struct scx_sched *sch, struct rq *rq, struct scx_dispatch_q *dsq, u64 enq_flags) { struct task_struct *p; retry: /* * The caller can't expect to successfully consume a task if the task's * addition to @dsq isn't guaranteed to be visible somehow. Test * @dsq->list without locking and skip if it seems empty. */ if (list_empty(&dsq->list)) return false; raw_spin_lock(&dsq->lock); nldsq_for_each_task(p, dsq) { struct rq *task_rq = task_rq(p); /* * This loop can lead to multiple lockup scenarios, e.g. the BPF * scheduler can put an enormous number of affinitized tasks into * a contended DSQ, or the outer retry loop can repeatedly race * against scx_bypass() dequeueing tasks from @dsq trying to put * the system into the bypass mode. This can easily live-lock the * machine. If aborting, exit from all non-bypass DSQs. */ if (unlikely(READ_ONCE(sch->aborting)) && dsq->id != SCX_DSQ_BYPASS) break; if (rq == task_rq) { task_unlink_from_dsq(p, dsq); move_local_task_to_local_dsq(p, enq_flags, dsq, rq); raw_spin_unlock(&dsq->lock); return true; } if (task_can_run_on_remote_rq(sch, p, rq, false)) { if (likely(consume_remote_task(rq, p, enq_flags, dsq, task_rq))) return true; goto retry; } } raw_spin_unlock(&dsq->lock); return false; } static bool consume_global_dsq(struct scx_sched *sch, struct rq *rq) { int node = cpu_to_node(cpu_of(rq)); return consume_dispatch_q(sch, rq, &sch->pnode[node]->global_dsq, 0); } /** * dispatch_to_local_dsq - Dispatch a task to a local dsq * @sch: scx_sched being operated on * @rq: current rq which is locked * @dst_dsq: destination DSQ * @p: task to dispatch * @enq_flags: %SCX_ENQ_* * * We're holding @rq lock and want to dispatch @p to @dst_dsq which is a local * DSQ. This function performs all the synchronization dancing needed because * local DSQs are protected with rq locks. * * The caller must have exclusive ownership of @p (e.g. through * %SCX_OPSS_DISPATCHING). */ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq, struct scx_dispatch_q *dst_dsq, struct task_struct *p, u64 enq_flags) { struct rq *src_rq = task_rq(p); struct rq *dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq); struct rq *locked_rq = rq; /* * We're synchronized against dequeue through DISPATCHING. As @p can't * be dequeued, its task_rq and cpus_allowed are stable too. * * If dispatching to @rq that @p is already on, no lock dancing needed. */ if (rq == src_rq && rq == dst_rq) { dispatch_enqueue(sch, rq, dst_dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS); return; } if (src_rq != dst_rq && unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) { dispatch_enqueue(sch, rq, find_global_dsq(sch, task_cpu(p)), p, enq_flags | SCX_ENQ_CLEAR_OPSS | SCX_ENQ_GDSQ_FALLBACK); return; } /* * @p is on a possibly remote @src_rq which we need to lock to move the * task. If dequeue is in progress, it'd be locking @src_rq and waiting * on DISPATCHING, so we can't grab @src_rq lock while holding * DISPATCHING. * * As DISPATCHING guarantees that @p is wholly ours, we can pretend that * we're moving from a DSQ and use the same mechanism - mark the task * under transfer with holding_cpu, release DISPATCHING and then follow * the same protocol. See unlink_dsq_and_lock_src_rq(). */ p->scx.holding_cpu = raw_smp_processor_id(); /* store_release ensures that dequeue sees the above */ atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE); /* switch to @src_rq lock */ if (locked_rq != src_rq) { raw_spin_rq_unlock(locked_rq); locked_rq = src_rq; raw_spin_rq_lock(src_rq); } /* task_rq couldn't have changed if we're still the holding cpu */ if (likely(p->scx.holding_cpu == raw_smp_processor_id()) && !WARN_ON_ONCE(src_rq != task_rq(p))) { /* * If @p is staying on the same rq, there's no need to go * through the full deactivate/activate cycle. Optimize by * abbreviating move_remote_task_to_local_dsq(). */ if (src_rq == dst_rq) { p->scx.holding_cpu = -1; dispatch_enqueue(sch, dst_rq, &dst_rq->scx.local_dsq, p, enq_flags); } else { move_remote_task_to_local_dsq(p, enq_flags, src_rq, dst_rq); /* task has been moved to dst_rq, which is now locked */ locked_rq = dst_rq; } /* if the destination CPU is idle, wake it up */ if (sched_class_above(p->sched_class, dst_rq->curr->sched_class)) resched_curr(dst_rq); } /* switch back to @rq lock */ if (locked_rq != rq) { raw_spin_rq_unlock(locked_rq); raw_spin_rq_lock(rq); } } /** * finish_dispatch - Asynchronously finish dispatching a task * @rq: current rq which is locked * @p: task to finish dispatching * @qseq_at_dispatch: qseq when @p started getting dispatched * @dsq_id: destination DSQ ID * @enq_flags: %SCX_ENQ_* * * Dispatching to local DSQs may need to wait for queueing to complete or * require rq lock dancing. As we don't wanna do either while inside * ops.dispatch() to avoid locking order inversion, we split dispatching into * two parts. scx_bpf_dsq_insert() which is called by ops.dispatch() records the * task and its qseq. Once ops.dispatch() returns, this function is called to * finish up. * * There is no guarantee that @p is still valid for dispatching or even that it * was valid in the first place. Make sure that the task is still owned by the * BPF scheduler and claim the ownership before dispatching. */ static void finish_dispatch(struct scx_sched *sch, struct rq *rq, struct task_struct *p, unsigned long qseq_at_dispatch, u64 dsq_id, u64 enq_flags) { struct scx_dispatch_q *dsq; unsigned long opss; touch_core_sched_dispatch(rq, p); retry: /* * No need for _acquire here. @p is accessed only after a successful * try_cmpxchg to DISPATCHING. */ opss = atomic_long_read(&p->scx.ops_state); switch (opss & SCX_OPSS_STATE_MASK) { case SCX_OPSS_DISPATCHING: case SCX_OPSS_NONE: /* someone else already got to it */ return; case SCX_OPSS_QUEUED: /* * If qseq doesn't match, @p has gone through at least one * dispatch/dequeue and re-enqueue cycle between * scx_bpf_dsq_insert() and here and we have no claim on it. */ if ((opss & SCX_OPSS_QSEQ_MASK) != qseq_at_dispatch) return; /* see SCX_EV_INSERT_NOT_OWNED definition */ if (unlikely(!scx_task_on_sched(sch, p))) { __scx_add_event(sch, SCX_EV_INSERT_NOT_OWNED, 1); return; } /* * While we know @p is accessible, we don't yet have a claim on * it - the BPF scheduler is allowed to dispatch tasks * spuriously and there can be a racing dequeue attempt. Let's * claim @p by atomically transitioning it from QUEUED to * DISPATCHING. */ if (likely(atomic_long_try_cmpxchg(&p->scx.ops_state, &opss, SCX_OPSS_DISPATCHING))) break; goto retry; case SCX_OPSS_QUEUEING: /* * do_enqueue_task() is in the process of transferring the task * to the BPF scheduler while holding @p's rq lock. As we aren't * holding any kernel or BPF resource that the enqueue path may * depend upon, it's safe to wait. */ wait_ops_state(p, opss); goto retry; } BUG_ON(!(p->scx.flags & SCX_TASK_QUEUED)); dsq = find_dsq_for_dispatch(sch, this_rq(), dsq_id, task_cpu(p)); if (dsq->id == SCX_DSQ_LOCAL) dispatch_to_local_dsq(sch, rq, dsq, p, enq_flags); else dispatch_enqueue(sch, rq, dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS); } static void flush_dispatch_buf(struct scx_sched *sch, struct rq *rq) { struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; u32 u; for (u = 0; u < dspc->cursor; u++) { struct scx_dsp_buf_ent *ent = &dspc->buf[u]; finish_dispatch(sch, rq, ent->task, ent->qseq, ent->dsq_id, ent->enq_flags); } dspc->nr_tasks += dspc->cursor; dspc->cursor = 0; } static inline void maybe_queue_balance_callback(struct rq *rq) { lockdep_assert_rq_held(rq); if (!(rq->scx.flags & SCX_RQ_BAL_CB_PENDING)) return; queue_balance_callback(rq, &rq->scx.deferred_bal_cb, deferred_bal_cb_workfn); rq->scx.flags &= ~SCX_RQ_BAL_CB_PENDING; } /* * One user of this function is scx_bpf_dispatch() which can be called * recursively as sub-sched dispatches nest. Always inline to reduce stack usage * from the call frame. */ static __always_inline bool scx_dispatch_sched(struct scx_sched *sch, struct rq *rq, struct task_struct *prev, bool nested) { struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; int nr_loops = SCX_DSP_MAX_LOOPS; s32 cpu = cpu_of(rq); bool prev_on_sch = (prev->sched_class == &ext_sched_class) && scx_task_on_sched(sch, prev); if (consume_global_dsq(sch, rq)) return true; if (bypass_dsp_enabled(sch)) { /* if @sch is bypassing, only the bypass DSQs are active */ if (scx_bypassing(sch, cpu)) return consume_dispatch_q(sch, rq, bypass_dsq(sch, cpu), 0); #ifdef CONFIG_EXT_SUB_SCHED /* * If @sch isn't bypassing but its children are, @sch is * responsible for making forward progress for both its own * tasks that aren't bypassing and the bypassing descendants' * tasks. The following implements a simple built-in behavior - * let each CPU try to run the bypass DSQ every Nth time. * * Later, if necessary, we can add an ops flag to suppress the * auto-consumption and a kfunc to consume the bypass DSQ and, * so that the BPF scheduler can fully control scheduling of * bypassed tasks. */ struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); if (!(pcpu->bypass_host_seq++ % SCX_BYPASS_HOST_NTH) && consume_dispatch_q(sch, rq, bypass_dsq(sch, cpu), 0)) { __scx_add_event(sch, SCX_EV_SUB_BYPASS_DISPATCH, 1); return true; } #endif /* CONFIG_EXT_SUB_SCHED */ } if (unlikely(!SCX_HAS_OP(sch, dispatch)) || !scx_rq_online(rq)) return false; dspc->rq = rq; /* * The dispatch loop. Because flush_dispatch_buf() may drop the rq lock, * the local DSQ might still end up empty after a successful * ops.dispatch(). If the local DSQ is empty even after ops.dispatch() * produced some tasks, retry. The BPF scheduler may depend on this * looping behavior to simplify its implementation. */ do { dspc->nr_tasks = 0; if (nested) { /* * If nested, don't update kf_mask as the originating * invocation would already have set it up. */ SCX_CALL_OP(sch, 0, dispatch, rq, cpu, prev_on_sch ? prev : NULL); } else { /* * If not nested, stash @prev so that nested invocations * can access it. */ rq->scx.sub_dispatch_prev = prev; SCX_CALL_OP(sch, SCX_KF_DISPATCH, dispatch, rq, cpu, prev_on_sch ? prev : NULL); rq->scx.sub_dispatch_prev = NULL; } flush_dispatch_buf(sch, rq); if ((prev->scx.flags & SCX_TASK_QUEUED) && prev->scx.slice) { rq->scx.flags |= SCX_RQ_BAL_KEEP; return true; } if (rq->scx.local_dsq.nr) return true; if (consume_global_dsq(sch, rq)) return true; /* * ops.dispatch() can trap us in this loop by repeatedly * dispatching ineligible tasks. Break out once in a while to * allow the watchdog to run. As IRQ can't be enabled in * balance(), we want to complete this scheduling cycle and then * start a new one. IOW, we want to call resched_curr() on the * next, most likely idle, task, not the current one. Use * __scx_bpf_kick_cpu() for deferred kicking. */ if (unlikely(!--nr_loops)) { scx_kick_cpu(sch, cpu, 0); break; } } while (dspc->nr_tasks); /* * Prevent the CPU from going idle while bypassed descendants have tasks * queued. Without this fallback, bypassed tasks could stall if the host * scheduler's ops.dispatch() doesn't yield any tasks. */ if (bypass_dsp_enabled(sch)) return consume_dispatch_q(sch, rq, bypass_dsq(sch, cpu), 0); return false; } static int balance_one(struct rq *rq, struct task_struct *prev) { struct scx_sched *sch = scx_root; s32 cpu = cpu_of(rq); lockdep_assert_rq_held(rq); rq->scx.flags |= SCX_RQ_IN_BALANCE; rq->scx.flags &= ~SCX_RQ_BAL_KEEP; if ((sch->ops.flags & SCX_OPS_HAS_CPU_PREEMPT) && unlikely(rq->scx.cpu_released)) { /* * If the previous sched_class for the current CPU was not SCX, * notify the BPF scheduler that it again has control of the * core. This callback complements ->cpu_release(), which is * emitted in switch_class(). */ if (SCX_HAS_OP(sch, cpu_acquire)) SCX_CALL_OP(sch, SCX_KF_REST, cpu_acquire, rq, cpu, NULL); rq->scx.cpu_released = false; } if (prev->sched_class == &ext_sched_class) { update_curr_scx(rq); /* * If @prev is runnable & has slice left, it has priority and * fetching more just increases latency for the fetched tasks. * Tell pick_task_scx() to keep running @prev. If the BPF * scheduler wants to handle this explicitly, it should * implement ->cpu_release(). * * See scx_disable_workfn() for the explanation on the bypassing * test. */ if ((prev->scx.flags & SCX_TASK_QUEUED) && prev->scx.slice && !scx_bypassing(sch, cpu)) { rq->scx.flags |= SCX_RQ_BAL_KEEP; goto has_tasks; } } /* if there already are tasks to run, nothing to do */ if (rq->scx.local_dsq.nr) goto has_tasks; if (scx_dispatch_sched(sch, rq, prev, false)) goto has_tasks; /* * Didn't find another task to run. Keep running @prev unless * %SCX_OPS_ENQ_LAST is in effect. */ if ((prev->scx.flags & SCX_TASK_QUEUED) && (!(sch->ops.flags & SCX_OPS_ENQ_LAST) || scx_bypassing(sch, cpu))) { rq->scx.flags |= SCX_RQ_BAL_KEEP; __scx_add_event(sch, SCX_EV_DISPATCH_KEEP_LAST, 1); goto has_tasks; } rq->scx.flags &= ~SCX_RQ_IN_BALANCE; return false; has_tasks: /* * @rq may have extra IMMED tasks without reenq scheduled: * * - rq_is_open() can't reliably tell when and how slice is going to be * modified for $curr and allows IMMED tasks to be queued while * dispatch is in progress. * * - A non-IMMED HEAD task can get queued in front of an IMMED task * between the IMMED queueing and the subsequent scheduling event. */ if (unlikely(rq->scx.local_dsq.nr > 1 && rq->scx.nr_immed)) schedule_reenq_local(rq, 0); rq->scx.flags &= ~SCX_RQ_IN_BALANCE; return true; } static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first) { struct scx_sched *sch = scx_task_sched(p); if (p->scx.flags & SCX_TASK_QUEUED) { /* * Core-sched might decide to execute @p before it is * dispatched. Call ops_dequeue() to notify the BPF scheduler. */ ops_dequeue(rq, p, SCX_DEQ_CORE_SCHED_EXEC); dispatch_dequeue(rq, p); } p->se.exec_start = rq_clock_task(rq); /* see dequeue_task_scx() on why we skip when !QUEUED */ if (SCX_HAS_OP(sch, running) && (p->scx.flags & SCX_TASK_QUEUED)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, running, rq, p); clr_task_runnable(p, true); /* * @p is getting newly scheduled or got kicked after someone updated its * slice. Refresh whether tick can be stopped. See scx_can_stop_tick(). */ if ((p->scx.slice == SCX_SLICE_INF) != (bool)(rq->scx.flags & SCX_RQ_CAN_STOP_TICK)) { if (p->scx.slice == SCX_SLICE_INF) rq->scx.flags |= SCX_RQ_CAN_STOP_TICK; else rq->scx.flags &= ~SCX_RQ_CAN_STOP_TICK; sched_update_tick_dependency(rq); /* * For now, let's refresh the load_avgs just when transitioning * in and out of nohz. In the future, we might want to add a * mechanism which calls the following periodically on * tick-stopped CPUs. */ update_other_load_avgs(rq); } } static enum scx_cpu_preempt_reason preempt_reason_from_class(const struct sched_class *class) { if (class == &stop_sched_class) return SCX_CPU_PREEMPT_STOP; if (class == &dl_sched_class) return SCX_CPU_PREEMPT_DL; if (class == &rt_sched_class) return SCX_CPU_PREEMPT_RT; return SCX_CPU_PREEMPT_UNKNOWN; } static void switch_class(struct rq *rq, struct task_struct *next) { struct scx_sched *sch = scx_root; const struct sched_class *next_class = next->sched_class; if (!(sch->ops.flags & SCX_OPS_HAS_CPU_PREEMPT)) return; /* * The callback is conceptually meant to convey that the CPU is no * longer under the control of SCX. Therefore, don't invoke the callback * if the next class is below SCX (in which case the BPF scheduler has * actively decided not to schedule any tasks on the CPU). */ if (sched_class_above(&ext_sched_class, next_class)) return; /* * At this point we know that SCX was preempted by a higher priority * sched_class, so invoke the ->cpu_release() callback if we have not * done so already. We only send the callback once between SCX being * preempted, and it regaining control of the CPU. * * ->cpu_release() complements ->cpu_acquire(), which is emitted the * next time that balance_one() is invoked. */ if (!rq->scx.cpu_released) { if (SCX_HAS_OP(sch, cpu_release)) { struct scx_cpu_release_args args = { .reason = preempt_reason_from_class(next_class), .task = next, }; SCX_CALL_OP(sch, SCX_KF_CPU_RELEASE, cpu_release, rq, cpu_of(rq), &args); } rq->scx.cpu_released = true; } } static void put_prev_task_scx(struct rq *rq, struct task_struct *p, struct task_struct *next) { struct scx_sched *sch = scx_task_sched(p); /* see kick_sync_wait_bal_cb() */ smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); update_curr_scx(rq); /* see dequeue_task_scx() on why we skip when !QUEUED */ if (SCX_HAS_OP(sch, stopping) && (p->scx.flags & SCX_TASK_QUEUED)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, stopping, rq, p, true); if (p->scx.flags & SCX_TASK_QUEUED) { set_task_runnable(rq, p); /* * If @p has slice left and is being put, @p is getting * preempted by a higher priority scheduler class or core-sched * forcing a different task. Leave it at the head of the local * DSQ unless it was an IMMED task. IMMED tasks should not * linger on a busy CPU, reenqueue them to the BPF scheduler. */ if (p->scx.slice && !scx_bypassing(sch, cpu_of(rq))) { if (p->scx.flags & SCX_TASK_IMMED) { p->scx.flags |= SCX_TASK_REENQ_PREEMPTED; do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1); p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; } else { dispatch_enqueue(sch, rq, &rq->scx.local_dsq, p, SCX_ENQ_HEAD); } goto switch_class; } /* * If @p is runnable but we're about to enter a lower * sched_class, %SCX_OPS_ENQ_LAST must be set. Tell * ops.enqueue() that @p is the only one available for this cpu, * which should trigger an explicit follow-up scheduling event. */ if (next && sched_class_above(&ext_sched_class, next->sched_class)) { WARN_ON_ONCE(!(sch->ops.flags & SCX_OPS_ENQ_LAST)); do_enqueue_task(rq, p, SCX_ENQ_LAST, -1); } else { do_enqueue_task(rq, p, 0, -1); } } switch_class: if (next && next->sched_class != &ext_sched_class) switch_class(rq, next); } static void kick_sync_wait_bal_cb(struct rq *rq) { struct scx_kick_syncs __rcu *ks = __this_cpu_read(scx_kick_syncs); unsigned long *ksyncs = rcu_dereference_sched(ks)->syncs; bool waited; s32 cpu; /* * Drop rq lock and enable IRQs while waiting. IRQs must be enabled * — a target CPU may be waiting for us to process an IPI (e.g. TLB * flush) while we wait for its kick_sync to advance. * * Also, keep advancing our own kick_sync so that new kick_sync waits * targeting us, which can start after we drop the lock, cannot form * cyclic dependencies. */ retry: waited = false; for_each_cpu(cpu, rq->scx.cpus_to_sync) { /* * smp_load_acquire() pairs with smp_store_release() on * kick_sync updates on the target CPUs. */ if (cpu == cpu_of(rq) || smp_load_acquire(&cpu_rq(cpu)->scx.kick_sync) != ksyncs[cpu]) { cpumask_clear_cpu(cpu, rq->scx.cpus_to_sync); continue; } raw_spin_rq_unlock_irq(rq); while (READ_ONCE(cpu_rq(cpu)->scx.kick_sync) == ksyncs[cpu]) { smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); cpu_relax(); } raw_spin_rq_lock_irq(rq); waited = true; } if (waited) goto retry; } static struct task_struct *first_local_task(struct rq *rq) { return list_first_entry_or_null(&rq->scx.local_dsq.list, struct task_struct, scx.dsq_list.node); } static struct task_struct * do_pick_task_scx(struct rq *rq, struct rq_flags *rf, bool force_scx) { struct task_struct *prev = rq->curr; bool keep_prev; struct task_struct *p; /* see kick_sync_wait_bal_cb() */ smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); rq_modified_begin(rq, &ext_sched_class); rq_unpin_lock(rq, rf); balance_one(rq, prev); rq_repin_lock(rq, rf); maybe_queue_balance_callback(rq); /* * Defer to a balance callback which can drop rq lock and enable * IRQs. Waiting directly in the pick path would deadlock against * CPUs sending us IPIs (e.g. TLB flushes) while we wait for them. */ if (unlikely(rq->scx.kick_sync_pending)) { rq->scx.kick_sync_pending = false; queue_balance_callback(rq, &rq->scx.kick_sync_bal_cb, kick_sync_wait_bal_cb); } /* * If any higher-priority sched class enqueued a runnable task on * this rq during balance_one(), abort and return RETRY_TASK, so * that the scheduler loop can restart. * * If @force_scx is true, always try to pick a SCHED_EXT task, * regardless of any higher-priority sched classes activity. */ if (!force_scx && rq_modified_above(rq, &ext_sched_class)) return RETRY_TASK; keep_prev = rq->scx.flags & SCX_RQ_BAL_KEEP; if (unlikely(keep_prev && prev->sched_class != &ext_sched_class)) { WARN_ON_ONCE(scx_enable_state() == SCX_ENABLED); keep_prev = false; } /* * If balance_one() is telling us to keep running @prev, replenish slice * if necessary and keep running @prev. Otherwise, pop the first one * from the local DSQ. */ if (keep_prev) { p = prev; if (!p->scx.slice) refill_task_slice_dfl(scx_task_sched(p), p); } else { p = first_local_task(rq); if (!p) return NULL; if (unlikely(!p->scx.slice)) { struct scx_sched *sch = scx_task_sched(p); if (!scx_bypassing(sch, cpu_of(rq)) && !sch->warned_zero_slice) { printk_deferred(KERN_WARNING "sched_ext: %s[%d] has zero slice in %s()\n", p->comm, p->pid, __func__); sch->warned_zero_slice = true; } refill_task_slice_dfl(sch, p); } } return p; } static struct task_struct *pick_task_scx(struct rq *rq, struct rq_flags *rf) { return do_pick_task_scx(rq, rf, false); } /* * Select the next task to run from the ext scheduling class. * * Use do_pick_task_scx() directly with @force_scx enabled, since the * dl_server must always select a sched_ext task. */ static struct task_struct * ext_server_pick_task(struct sched_dl_entity *dl_se, struct rq_flags *rf) { if (!scx_enabled()) return NULL; return do_pick_task_scx(dl_se->rq, rf, true); } /* * Initialize the ext server deadline entity. */ void ext_server_init(struct rq *rq) { struct sched_dl_entity *dl_se = &rq->ext_server; init_dl_entity(dl_se); dl_server_init(dl_se, rq, ext_server_pick_task); } #ifdef CONFIG_SCHED_CORE /** * scx_prio_less - Task ordering for core-sched * @a: task A * @b: task B * @in_fi: in forced idle state * * Core-sched is implemented as an additional scheduling layer on top of the * usual sched_class'es and needs to find out the expected task ordering. For * SCX, core-sched calls this function to interrogate the task ordering. * * Unless overridden by ops.core_sched_before(), @p->scx.core_sched_at is used * to implement the default task ordering. The older the timestamp, the higher * priority the task - the global FIFO ordering matching the default scheduling * behavior. * * When ops.core_sched_before() is enabled, @p->scx.core_sched_at is used to * implement FIFO ordering within each local DSQ. See pick_task_scx(). */ bool scx_prio_less(const struct task_struct *a, const struct task_struct *b, bool in_fi) { struct scx_sched *sch_a = scx_task_sched(a); struct scx_sched *sch_b = scx_task_sched(b); /* * The const qualifiers are dropped from task_struct pointers when * calling ops.core_sched_before(). Accesses are controlled by the * verifier. */ if (sch_a == sch_b && SCX_HAS_OP(sch_a, core_sched_before) && !scx_bypassing(sch_a, task_cpu(a))) return SCX_CALL_OP_2TASKS_RET(sch_a, SCX_KF_REST, core_sched_before, NULL, (struct task_struct *)a, (struct task_struct *)b); else return time_after64(a->scx.core_sched_at, b->scx.core_sched_at); } #endif /* CONFIG_SCHED_CORE */ static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flags) { struct scx_sched *sch = scx_task_sched(p); bool bypassing; /* * sched_exec() calls with %WF_EXEC when @p is about to exec(2) as it * can be a good migration opportunity with low cache and memory * footprint. Returning a CPU different than @prev_cpu triggers * immediate rq migration. However, for SCX, as the current rq * association doesn't dictate where the task is going to run, this * doesn't fit well. If necessary, we can later add a dedicated method * which can decide to preempt self to force it through the regular * scheduling path. */ if (unlikely(wake_flags & WF_EXEC)) return prev_cpu; bypassing = scx_bypassing(sch, task_cpu(p)); if (likely(SCX_HAS_OP(sch, select_cpu)) && !bypassing) { s32 cpu; struct task_struct **ddsp_taskp; ddsp_taskp = this_cpu_ptr(&direct_dispatch_task); WARN_ON_ONCE(*ddsp_taskp); *ddsp_taskp = p; cpu = SCX_CALL_OP_TASK_RET(sch, SCX_KF_ENQUEUE | SCX_KF_SELECT_CPU, select_cpu, NULL, p, prev_cpu, wake_flags); p->scx.selected_cpu = cpu; *ddsp_taskp = NULL; if (ops_cpu_valid(sch, cpu, "from ops.select_cpu()")) return cpu; else return prev_cpu; } else { s32 cpu; cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags, NULL, 0); if (cpu >= 0) { refill_task_slice_dfl(sch, p); p->scx.ddsp_dsq_id = SCX_DSQ_LOCAL; } else { cpu = prev_cpu; } p->scx.selected_cpu = cpu; if (bypassing) __scx_add_event(sch, SCX_EV_BYPASS_DISPATCH, 1); return cpu; } } static void task_woken_scx(struct rq *rq, struct task_struct *p) { run_deferred(rq); } static void set_cpus_allowed_scx(struct task_struct *p, struct affinity_context *ac) { struct scx_sched *sch = scx_task_sched(p); set_cpus_allowed_common(p, ac); if (task_dead_and_done(p)) return; /* * The effective cpumask is stored in @p->cpus_ptr which may temporarily * differ from the configured one in @p->cpus_mask. Always tell the bpf * scheduler the effective one. * * Fine-grained memory write control is enforced by BPF making the const * designation pointless. Cast it away when calling the operation. */ if (SCX_HAS_OP(sch, set_cpumask)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_cpumask, NULL, p, (struct cpumask *)p->cpus_ptr); } static void handle_hotplug(struct rq *rq, bool online) { struct scx_sched *sch = scx_root; s32 cpu = cpu_of(rq); atomic_long_inc(&scx_hotplug_seq); /* * scx_root updates are protected by cpus_read_lock() and will stay * stable here. Note that we can't depend on scx_enabled() test as the * hotplug ops need to be enabled before __scx_enabled is set. */ if (unlikely(!sch)) return; if (scx_enabled()) scx_idle_update_selcpu_topology(&sch->ops); if (online && SCX_HAS_OP(sch, cpu_online)) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cpu_online, NULL, cpu); else if (!online && SCX_HAS_OP(sch, cpu_offline)) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cpu_offline, NULL, cpu); else scx_exit(sch, SCX_EXIT_UNREG_KERN, SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG, "cpu %d going %s, exiting scheduler", cpu, online ? "online" : "offline"); } void scx_rq_activate(struct rq *rq) { handle_hotplug(rq, true); } void scx_rq_deactivate(struct rq *rq) { handle_hotplug(rq, false); } static void rq_online_scx(struct rq *rq) { rq->scx.flags |= SCX_RQ_ONLINE; } static void rq_offline_scx(struct rq *rq) { rq->scx.flags &= ~SCX_RQ_ONLINE; } static bool check_rq_for_timeouts(struct rq *rq) { struct scx_sched *sch; struct task_struct *p; struct rq_flags rf; bool timed_out = false; rq_lock_irqsave(rq, &rf); sch = rcu_dereference_bh(scx_root); if (unlikely(!sch)) goto out_unlock; list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) { struct scx_sched *sch = scx_task_sched(p); unsigned long last_runnable = p->scx.runnable_at; if (unlikely(time_after(jiffies, last_runnable + READ_ONCE(sch->watchdog_timeout)))) { u32 dur_ms = jiffies_to_msecs(jiffies - last_runnable); scx_exit(sch, SCX_EXIT_ERROR_STALL, 0, "%s[%d] failed to run for %u.%03us", p->comm, p->pid, dur_ms / 1000, dur_ms % 1000); timed_out = true; break; } } out_unlock: rq_unlock_irqrestore(rq, &rf); return timed_out; } static void scx_watchdog_workfn(struct work_struct *work) { unsigned long intv; int cpu; WRITE_ONCE(scx_watchdog_timestamp, jiffies); for_each_online_cpu(cpu) { if (unlikely(check_rq_for_timeouts(cpu_rq(cpu)))) break; cond_resched(); } intv = READ_ONCE(scx_watchdog_interval); if (intv < ULONG_MAX) queue_delayed_work(system_dfl_wq, to_delayed_work(work), intv); } void scx_tick(struct rq *rq) { struct scx_sched *root; unsigned long last_check; if (!scx_enabled()) return; root = rcu_dereference_bh(scx_root); if (unlikely(!root)) return; last_check = READ_ONCE(scx_watchdog_timestamp); if (unlikely(time_after(jiffies, last_check + READ_ONCE(root->watchdog_timeout)))) { u32 dur_ms = jiffies_to_msecs(jiffies - last_check); scx_exit(root, SCX_EXIT_ERROR_STALL, 0, "watchdog failed to check in for %u.%03us", dur_ms / 1000, dur_ms % 1000); } update_other_load_avgs(rq); } static void task_tick_scx(struct rq *rq, struct task_struct *curr, int queued) { struct scx_sched *sch = scx_task_sched(curr); update_curr_scx(rq); /* * While disabling, always resched and refresh core-sched timestamp as * we can't trust the slice management or ops.core_sched_before(). */ if (scx_bypassing(sch, cpu_of(rq))) { curr->scx.slice = 0; touch_core_sched(rq, curr); } else if (SCX_HAS_OP(sch, tick)) { SCX_CALL_OP_TASK(sch, SCX_KF_REST, tick, rq, curr); } if (!curr->scx.slice) resched_curr(rq); } #ifdef CONFIG_EXT_GROUP_SCHED static struct cgroup *tg_cgrp(struct task_group *tg) { /* * If CGROUP_SCHED is disabled, @tg is NULL. If @tg is an autogroup, * @tg->css.cgroup is NULL. In both cases, @tg can be treated as the * root cgroup. */ if (tg && tg->css.cgroup) return tg->css.cgroup; else return &cgrp_dfl_root.cgrp; } #define SCX_INIT_TASK_ARGS_CGROUP(tg) .cgroup = tg_cgrp(tg), #else /* CONFIG_EXT_GROUP_SCHED */ #define SCX_INIT_TASK_ARGS_CGROUP(tg) #endif /* CONFIG_EXT_GROUP_SCHED */ static u32 scx_get_task_state(const struct task_struct *p) { return p->scx.flags & SCX_TASK_STATE_MASK; } static void scx_set_task_state(struct task_struct *p, u32 state) { u32 prev_state = scx_get_task_state(p); bool warn = false; switch (state) { case SCX_TASK_NONE: break; case SCX_TASK_INIT: warn = prev_state != SCX_TASK_NONE; break; case SCX_TASK_READY: warn = prev_state == SCX_TASK_NONE; break; case SCX_TASK_ENABLED: warn = prev_state != SCX_TASK_READY; break; default: warn = true; return; } WARN_ONCE(warn, "sched_ext: Invalid task state transition 0x%x -> 0x%x for %s[%d]", prev_state, state, p->comm, p->pid); p->scx.flags &= ~SCX_TASK_STATE_MASK; p->scx.flags |= state; } static int __scx_init_task(struct scx_sched *sch, struct task_struct *p, bool fork) { int ret; p->scx.disallow = false; if (SCX_HAS_OP(sch, init_task)) { struct scx_init_task_args args = { SCX_INIT_TASK_ARGS_CGROUP(task_group(p)) .fork = fork, }; ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, init_task, NULL, p, &args); if (unlikely(ret)) { ret = ops_sanitize_err(sch, "init_task", ret); return ret; } } if (p->scx.disallow) { if (unlikely(scx_parent(sch))) { scx_error(sch, "non-root ops.init_task() set task->scx.disallow for %s[%d]", p->comm, p->pid); } else if (unlikely(fork)) { scx_error(sch, "ops.init_task() set task->scx.disallow for %s[%d] during fork", p->comm, p->pid); } else { struct rq *rq; struct rq_flags rf; rq = task_rq_lock(p, &rf); /* * We're in the load path and @p->policy will be applied * right after. Reverting @p->policy here and rejecting * %SCHED_EXT transitions from scx_check_setscheduler() * guarantees that if ops.init_task() sets @p->disallow, * @p can never be in SCX. */ if (p->policy == SCHED_EXT) { p->policy = SCHED_NORMAL; atomic_long_inc(&scx_nr_rejected); } task_rq_unlock(rq, p, &rf); } } return 0; } static int scx_init_task(struct scx_sched *sch, struct task_struct *p, bool fork) { int ret; ret = __scx_init_task(sch, p, fork); if (!ret) { /* * While @p's rq is not locked. @p is not visible to the rest of * SCX yet and it's safe to update the flags and state. */ p->scx.flags |= SCX_TASK_RESET_RUNNABLE_AT; scx_set_task_state(p, SCX_TASK_INIT); } return ret; } static void __scx_enable_task(struct scx_sched *sch, struct task_struct *p) { struct rq *rq = task_rq(p); u32 weight; lockdep_assert_rq_held(rq); /* * Verify the task is not in BPF scheduler's custody. If flag * transitions are consistent, the flag should always be clear * here. */ WARN_ON_ONCE(p->scx.flags & SCX_TASK_IN_CUSTODY); /* * Set the weight before calling ops.enable() so that the scheduler * doesn't see a stale value if they inspect the task struct. */ if (task_has_idle_policy(p)) weight = WEIGHT_IDLEPRIO; else weight = sched_prio_to_weight[p->static_prio - MAX_RT_PRIO]; p->scx.weight = sched_weight_to_cgroup(weight); if (SCX_HAS_OP(sch, enable)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, enable, rq, p); if (SCX_HAS_OP(sch, set_weight)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_weight, rq, p, p->scx.weight); } static void scx_enable_task(struct scx_sched *sch, struct task_struct *p) { __scx_enable_task(sch, p); scx_set_task_state(p, SCX_TASK_ENABLED); } static void scx_disable_task(struct scx_sched *sch, struct task_struct *p) { struct rq *rq = task_rq(p); lockdep_assert_rq_held(rq); WARN_ON_ONCE(scx_get_task_state(p) != SCX_TASK_ENABLED); if (SCX_HAS_OP(sch, disable)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, disable, rq, p); scx_set_task_state(p, SCX_TASK_READY); /* * Verify the task is not in BPF scheduler's custody. If flag * transitions are consistent, the flag should always be clear * here. */ WARN_ON_ONCE(p->scx.flags & SCX_TASK_IN_CUSTODY); } static void __scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p) { struct scx_exit_task_args args = { .cancelled = false, }; lockdep_assert_held(&p->pi_lock); lockdep_assert_rq_held(task_rq(p)); switch (scx_get_task_state(p)) { case SCX_TASK_NONE: return; case SCX_TASK_INIT: args.cancelled = true; break; case SCX_TASK_READY: break; case SCX_TASK_ENABLED: scx_disable_task(sch, p); break; default: WARN_ON_ONCE(true); return; } if (SCX_HAS_OP(sch, exit_task)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, exit_task, task_rq(p), p, &args); } static void scx_disable_and_exit_task(struct scx_sched *sch, struct task_struct *p) { __scx_disable_and_exit_task(sch, p); /* * If set, @p exited between __scx_init_task() and scx_enable_task() in * scx_sub_enable() and is initialized for both the associated sched and * its parent. Disable and exit for the child too. */ if ((p->scx.flags & SCX_TASK_SUB_INIT) && !WARN_ON_ONCE(!scx_enabling_sub_sched)) { __scx_disable_and_exit_task(scx_enabling_sub_sched, p); p->scx.flags &= ~SCX_TASK_SUB_INIT; } scx_set_task_sched(p, NULL); scx_set_task_state(p, SCX_TASK_NONE); } void init_scx_entity(struct sched_ext_entity *scx) { memset(scx, 0, sizeof(*scx)); INIT_LIST_HEAD(&scx->dsq_list.node); RB_CLEAR_NODE(&scx->dsq_priq); scx->sticky_cpu = -1; scx->holding_cpu = -1; INIT_LIST_HEAD(&scx->runnable_node); scx->runnable_at = jiffies; scx->ddsp_dsq_id = SCX_DSQ_INVALID; scx->slice = SCX_SLICE_DFL; } void scx_pre_fork(struct task_struct *p) { /* * BPF scheduler enable/disable paths want to be able to iterate and * update all tasks which can become complex when racing forks. As * enable/disable are very cold paths, let's use a percpu_rwsem to * exclude forks. */ percpu_down_read(&scx_fork_rwsem); } int scx_fork(struct task_struct *p, struct kernel_clone_args *kargs) { s32 ret; percpu_rwsem_assert_held(&scx_fork_rwsem); if (scx_init_task_enabled) { #ifdef CONFIG_EXT_SUB_SCHED struct scx_sched *sch = kargs->cset->dfl_cgrp->scx_sched; #else struct scx_sched *sch = scx_root; #endif ret = scx_init_task(sch, p, true); if (!ret) scx_set_task_sched(p, sch); return ret; } return 0; } void scx_post_fork(struct task_struct *p) { if (scx_init_task_enabled) { scx_set_task_state(p, SCX_TASK_READY); /* * Enable the task immediately if it's running on sched_ext. * Otherwise, it'll be enabled in switching_to_scx() if and * when it's ever configured to run with a SCHED_EXT policy. */ if (p->sched_class == &ext_sched_class) { struct rq_flags rf; struct rq *rq; rq = task_rq_lock(p, &rf); scx_enable_task(scx_task_sched(p), p); task_rq_unlock(rq, p, &rf); } } raw_spin_lock_irq(&scx_tasks_lock); list_add_tail(&p->scx.tasks_node, &scx_tasks); raw_spin_unlock_irq(&scx_tasks_lock); percpu_up_read(&scx_fork_rwsem); } void scx_cancel_fork(struct task_struct *p) { if (scx_enabled()) { struct rq *rq; struct rq_flags rf; rq = task_rq_lock(p, &rf); WARN_ON_ONCE(scx_get_task_state(p) >= SCX_TASK_READY); scx_disable_and_exit_task(scx_task_sched(p), p); task_rq_unlock(rq, p, &rf); } percpu_up_read(&scx_fork_rwsem); } /** * task_dead_and_done - Is a task dead and done running? * @p: target task * * Once sched_ext_dead() removes the dead task from scx_tasks and exits it, the * task no longer exists from SCX's POV. However, certain sched_class ops may be * invoked on these dead tasks leading to failures - e.g. sched_setscheduler() * may try to switch a task which finished sched_ext_dead() back into SCX * triggering invalid SCX task state transitions and worse. * * Once a task has finished the final switch, sched_ext_dead() is the only thing * that needs to happen on the task. Use this test to short-circuit sched_class * operations which may be called on dead tasks. */ static bool task_dead_and_done(struct task_struct *p) { struct rq *rq = task_rq(p); lockdep_assert_rq_held(rq); /* * In do_task_dead(), a dying task sets %TASK_DEAD with preemption * disabled and __schedule(). If @p has %TASK_DEAD set and off CPU, @p * won't ever run again. */ return unlikely(READ_ONCE(p->__state) == TASK_DEAD) && !task_on_cpu(rq, p); } void sched_ext_dead(struct task_struct *p) { unsigned long flags; /* * By the time control reaches here, @p has %TASK_DEAD set, switched out * for the last time and then dropped the rq lock - task_dead_and_done() * should be returning %true nullifying the straggling sched_class ops. * Remove from scx_tasks and exit @p. */ raw_spin_lock_irqsave(&scx_tasks_lock, flags); list_del_init(&p->scx.tasks_node); raw_spin_unlock_irqrestore(&scx_tasks_lock, flags); /* * @p is off scx_tasks and wholly ours. scx_root_enable()'s READY -> * ENABLED transitions can't race us. Disable ops for @p. */ if (scx_get_task_state(p) != SCX_TASK_NONE) { struct rq_flags rf; struct rq *rq; rq = task_rq_lock(p, &rf); scx_disable_and_exit_task(scx_task_sched(p), p); task_rq_unlock(rq, p, &rf); } } static void reweight_task_scx(struct rq *rq, struct task_struct *p, const struct load_weight *lw) { struct scx_sched *sch = scx_task_sched(p); lockdep_assert_rq_held(task_rq(p)); if (task_dead_and_done(p)) return; p->scx.weight = sched_weight_to_cgroup(scale_load_down(lw->weight)); if (SCX_HAS_OP(sch, set_weight)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_weight, rq, p, p->scx.weight); } static void prio_changed_scx(struct rq *rq, struct task_struct *p, u64 oldprio) { } static void switching_to_scx(struct rq *rq, struct task_struct *p) { struct scx_sched *sch = scx_task_sched(p); if (task_dead_and_done(p)) return; scx_enable_task(sch, p); /* * set_cpus_allowed_scx() is not called while @p is associated with a * different scheduler class. Keep the BPF scheduler up-to-date. */ if (SCX_HAS_OP(sch, set_cpumask)) SCX_CALL_OP_TASK(sch, SCX_KF_REST, set_cpumask, rq, p, (struct cpumask *)p->cpus_ptr); } static void switched_from_scx(struct rq *rq, struct task_struct *p) { if (task_dead_and_done(p)) return; scx_disable_task(scx_task_sched(p), p); } static void switched_to_scx(struct rq *rq, struct task_struct *p) {} int scx_check_setscheduler(struct task_struct *p, int policy) { lockdep_assert_rq_held(task_rq(p)); /* if disallow, reject transitioning into SCX */ if (scx_enabled() && READ_ONCE(p->scx.disallow) && p->policy != policy && policy == SCHED_EXT) return -EACCES; return 0; } static void process_ddsp_deferred_locals(struct rq *rq) { struct task_struct *p; lockdep_assert_rq_held(rq); /* * Now that @rq can be unlocked, execute the deferred enqueueing of * tasks directly dispatched to the local DSQs of other CPUs. See * direct_dispatch(). Keep popping from the head instead of using * list_for_each_entry_safe() as dispatch_local_dsq() may unlock @rq * temporarily. */ while ((p = list_first_entry_or_null(&rq->scx.ddsp_deferred_locals, struct task_struct, scx.dsq_list.node))) { struct scx_sched *sch = scx_task_sched(p); struct scx_dispatch_q *dsq; list_del_init(&p->scx.dsq_list.node); dsq = find_dsq_for_dispatch(sch, rq, p->scx.ddsp_dsq_id, task_cpu(p)); if (!WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL)) dispatch_to_local_dsq(sch, rq, dsq, p, p->scx.ddsp_enq_flags); } } /* * Determine whether @p should be reenqueued from a local DSQ. * * @reenq_flags is mutable and accumulates state across the DSQ walk: * * - %SCX_REENQ_TSR_NOT_FIRST: Set after the first task is visited. "First" * tracks position in the DSQ list, not among IMMED tasks. A non-IMMED task at * the head consumes the first slot. * * - %SCX_REENQ_TSR_RQ_OPEN: Set by reenq_local() before the walk if * rq_is_open() is true. * * An IMMED task is kept (returns %false) only if it's the first task in the DSQ * AND the current task is done — i.e. it will execute immediately. All other * IMMED tasks are reenqueued. This means if a non-IMMED task sits at the head, * every IMMED task behind it gets reenqueued. * * Reenqueued tasks go through ops.enqueue() with %SCX_ENQ_REENQ | * %SCX_TASK_REENQ_IMMED. If the BPF scheduler dispatches back to the same local * DSQ with %SCX_ENQ_IMMED while the CPU is still unavailable, this triggers * another reenq cycle. Repetitions are bounded by %SCX_REENQ_LOCAL_MAX_REPEAT * in process_deferred_reenq_locals(). */ static bool local_task_should_reenq(struct task_struct *p, u64 *reenq_flags, u32 *reason) { bool first; first = !(*reenq_flags & SCX_REENQ_TSR_NOT_FIRST); *reenq_flags |= SCX_REENQ_TSR_NOT_FIRST; *reason = SCX_TASK_REENQ_KFUNC; if ((p->scx.flags & SCX_TASK_IMMED) && (!first || !(*reenq_flags & SCX_REENQ_TSR_RQ_OPEN))) { __scx_add_event(scx_task_sched(p), SCX_EV_REENQ_IMMED, 1); *reason = SCX_TASK_REENQ_IMMED; return true; } return *reenq_flags & SCX_REENQ_ANY; } static u32 reenq_local(struct scx_sched *sch, struct rq *rq, u64 reenq_flags) { LIST_HEAD(tasks); u32 nr_enqueued = 0; struct task_struct *p, *n; lockdep_assert_rq_held(rq); if (WARN_ON_ONCE(reenq_flags & __SCX_REENQ_TSR_MASK)) reenq_flags &= ~__SCX_REENQ_TSR_MASK; if (rq_is_open(rq, 0)) reenq_flags |= SCX_REENQ_TSR_RQ_OPEN; /* * The BPF scheduler may choose to dispatch tasks back to * @rq->scx.local_dsq. Move all candidate tasks off to a private list * first to avoid processing the same tasks repeatedly. */ list_for_each_entry_safe(p, n, &rq->scx.local_dsq.list, scx.dsq_list.node) { struct scx_sched *task_sch = scx_task_sched(p); u32 reason; /* * If @p is being migrated, @p's current CPU may not agree with * its allowed CPUs and the migration_cpu_stop is about to * deactivate and re-activate @p anyway. Skip re-enqueueing. * * While racing sched property changes may also dequeue and * re-enqueue a migrating task while its current CPU and allowed * CPUs disagree, they use %ENQUEUE_RESTORE which is bypassed to * the current local DSQ for running tasks and thus are not * visible to the BPF scheduler. */ if (p->migration_pending) continue; if (!scx_is_descendant(task_sch, sch)) continue; if (!local_task_should_reenq(p, &reenq_flags, &reason)) continue; dispatch_dequeue(rq, p); if (WARN_ON_ONCE(p->scx.flags & SCX_TASK_REENQ_REASON_MASK)) p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; p->scx.flags |= reason; list_add_tail(&p->scx.dsq_list.node, &tasks); } list_for_each_entry_safe(p, n, &tasks, scx.dsq_list.node) { list_del_init(&p->scx.dsq_list.node); do_enqueue_task(rq, p, SCX_ENQ_REENQ, -1); p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; nr_enqueued++; } return nr_enqueued; } static void process_deferred_reenq_locals(struct rq *rq) { u64 seq = ++rq->scx.deferred_reenq_locals_seq; lockdep_assert_rq_held(rq); while (true) { struct scx_sched *sch; u64 reenq_flags; bool skip = false; scoped_guard (raw_spinlock, &rq->scx.deferred_reenq_lock) { struct scx_deferred_reenq_local *drl = list_first_entry_or_null(&rq->scx.deferred_reenq_locals, struct scx_deferred_reenq_local, node); struct scx_sched_pcpu *sch_pcpu; if (!drl) return; sch_pcpu = container_of(drl, struct scx_sched_pcpu, deferred_reenq_local); sch = sch_pcpu->sch; reenq_flags = drl->flags; WRITE_ONCE(drl->flags, 0); list_del_init(&drl->node); if (likely(drl->seq != seq)) { drl->seq = seq; drl->cnt = 0; } else { if (unlikely(++drl->cnt > SCX_REENQ_LOCAL_MAX_REPEAT)) { scx_error(sch, "SCX_ENQ_REENQ on SCX_DSQ_LOCAL repeated %u times", drl->cnt); skip = true; } __scx_add_event(sch, SCX_EV_REENQ_LOCAL_REPEAT, 1); } } if (!skip) { /* see schedule_dsq_reenq() */ smp_mb(); reenq_local(sch, rq, reenq_flags); } } } static bool user_task_should_reenq(struct task_struct *p, u64 reenq_flags, u32 *reason) { *reason = SCX_TASK_REENQ_KFUNC; return reenq_flags & SCX_REENQ_ANY; } static void reenq_user(struct rq *rq, struct scx_dispatch_q *dsq, u64 reenq_flags) { struct rq *locked_rq = rq; struct scx_sched *sch = dsq->sched; struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, dsq, 0); struct task_struct *p; s32 nr_enqueued = 0; lockdep_assert_rq_held(rq); raw_spin_lock(&dsq->lock); while (likely(!READ_ONCE(sch->bypass_depth))) { struct rq *task_rq; u32 reason; p = nldsq_cursor_next_task(&cursor, dsq); if (!p) break; if (!user_task_should_reenq(p, reenq_flags, &reason)) continue; task_rq = task_rq(p); if (locked_rq != task_rq) { if (locked_rq) raw_spin_rq_unlock(locked_rq); if (unlikely(!raw_spin_rq_trylock(task_rq))) { raw_spin_unlock(&dsq->lock); raw_spin_rq_lock(task_rq); raw_spin_lock(&dsq->lock); } locked_rq = task_rq; /* did we lose @p while switching locks? */ if (nldsq_cursor_lost_task(&cursor, task_rq, dsq, p)) continue; } /* @p is on @dsq, its rq and @dsq are locked */ dispatch_dequeue_locked(p, dsq); raw_spin_unlock(&dsq->lock); if (WARN_ON_ONCE(p->scx.flags & SCX_TASK_REENQ_REASON_MASK)) p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; p->scx.flags |= reason; do_enqueue_task(task_rq, p, SCX_ENQ_REENQ, -1); p->scx.flags &= ~SCX_TASK_REENQ_REASON_MASK; if (!(++nr_enqueued % SCX_TASK_ITER_BATCH)) { raw_spin_rq_unlock(locked_rq); locked_rq = NULL; cpu_relax(); } raw_spin_lock(&dsq->lock); } list_del_init(&cursor.node); raw_spin_unlock(&dsq->lock); if (locked_rq != rq) { if (locked_rq) raw_spin_rq_unlock(locked_rq); raw_spin_rq_lock(rq); } } static void process_deferred_reenq_users(struct rq *rq) { lockdep_assert_rq_held(rq); while (true) { struct scx_dispatch_q *dsq; u64 reenq_flags; scoped_guard (raw_spinlock, &rq->scx.deferred_reenq_lock) { struct scx_deferred_reenq_user *dru = list_first_entry_or_null(&rq->scx.deferred_reenq_users, struct scx_deferred_reenq_user, node); struct scx_dsq_pcpu *dsq_pcpu; if (!dru) return; dsq_pcpu = container_of(dru, struct scx_dsq_pcpu, deferred_reenq_user); dsq = dsq_pcpu->dsq; reenq_flags = dru->flags; WRITE_ONCE(dru->flags, 0); list_del_init(&dru->node); } /* see schedule_dsq_reenq() */ smp_mb(); BUG_ON(dsq->id & SCX_DSQ_FLAG_BUILTIN); reenq_user(rq, dsq, reenq_flags); } } static void run_deferred(struct rq *rq) { process_ddsp_deferred_locals(rq); if (!list_empty(&rq->scx.deferred_reenq_locals)) process_deferred_reenq_locals(rq); if (!list_empty(&rq->scx.deferred_reenq_users)) process_deferred_reenq_users(rq); } #ifdef CONFIG_NO_HZ_FULL bool scx_can_stop_tick(struct rq *rq) { struct task_struct *p = rq->curr; struct scx_sched *sch = scx_task_sched(p); if (p->sched_class != &ext_sched_class) return true; if (scx_bypassing(sch, cpu_of(rq))) return false; /* * @rq can dispatch from different DSQs, so we can't tell whether it * needs the tick or not by looking at nr_running. Allow stopping ticks * iff the BPF scheduler indicated so. See set_next_task_scx(). */ return rq->scx.flags & SCX_RQ_CAN_STOP_TICK; } #endif #ifdef CONFIG_EXT_GROUP_SCHED DEFINE_STATIC_PERCPU_RWSEM(scx_cgroup_ops_rwsem); static bool scx_cgroup_enabled; void scx_tg_init(struct task_group *tg) { tg->scx.weight = CGROUP_WEIGHT_DFL; tg->scx.bw_period_us = default_bw_period_us(); tg->scx.bw_quota_us = RUNTIME_INF; tg->scx.idle = false; } int scx_tg_online(struct task_group *tg) { struct scx_sched *sch = scx_root; int ret = 0; WARN_ON_ONCE(tg->scx.flags & (SCX_TG_ONLINE | SCX_TG_INITED)); if (scx_cgroup_enabled) { if (SCX_HAS_OP(sch, cgroup_init)) { struct scx_cgroup_init_args args = { .weight = tg->scx.weight, .bw_period_us = tg->scx.bw_period_us, .bw_quota_us = tg->scx.bw_quota_us, .bw_burst_us = tg->scx.bw_burst_us }; ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, cgroup_init, NULL, tg->css.cgroup, &args); if (ret) ret = ops_sanitize_err(sch, "cgroup_init", ret); } if (ret == 0) tg->scx.flags |= SCX_TG_ONLINE | SCX_TG_INITED; } else { tg->scx.flags |= SCX_TG_ONLINE; } return ret; } void scx_tg_offline(struct task_group *tg) { struct scx_sched *sch = scx_root; WARN_ON_ONCE(!(tg->scx.flags & SCX_TG_ONLINE)); if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_exit) && (tg->scx.flags & SCX_TG_INITED)) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_exit, NULL, tg->css.cgroup); tg->scx.flags &= ~(SCX_TG_ONLINE | SCX_TG_INITED); } int scx_cgroup_can_attach(struct cgroup_taskset *tset) { struct scx_sched *sch = scx_root; struct cgroup_subsys_state *css; struct task_struct *p; int ret; if (!scx_cgroup_enabled) return 0; cgroup_taskset_for_each(p, css, tset) { struct cgroup *from = tg_cgrp(task_group(p)); struct cgroup *to = tg_cgrp(css_tg(css)); WARN_ON_ONCE(p->scx.cgrp_moving_from); /* * sched_move_task() omits identity migrations. Let's match the * behavior so that ops.cgroup_prep_move() and ops.cgroup_move() * always match one-to-one. */ if (from == to) continue; if (SCX_HAS_OP(sch, cgroup_prep_move)) { ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, cgroup_prep_move, NULL, p, from, css->cgroup); if (ret) goto err; } p->scx.cgrp_moving_from = from; } return 0; err: cgroup_taskset_for_each(p, css, tset) { if (SCX_HAS_OP(sch, cgroup_cancel_move) && p->scx.cgrp_moving_from) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_cancel_move, NULL, p, p->scx.cgrp_moving_from, css->cgroup); p->scx.cgrp_moving_from = NULL; } return ops_sanitize_err(sch, "cgroup_prep_move", ret); } void scx_cgroup_move_task(struct task_struct *p) { struct scx_sched *sch = scx_root; if (!scx_cgroup_enabled) return; /* * @p must have ops.cgroup_prep_move() called on it and thus * cgrp_moving_from set. */ if (SCX_HAS_OP(sch, cgroup_move) && !WARN_ON_ONCE(!p->scx.cgrp_moving_from)) SCX_CALL_OP_TASK(sch, SCX_KF_UNLOCKED, cgroup_move, NULL, p, p->scx.cgrp_moving_from, tg_cgrp(task_group(p))); p->scx.cgrp_moving_from = NULL; } void scx_cgroup_cancel_attach(struct cgroup_taskset *tset) { struct scx_sched *sch = scx_root; struct cgroup_subsys_state *css; struct task_struct *p; if (!scx_cgroup_enabled) return; cgroup_taskset_for_each(p, css, tset) { if (SCX_HAS_OP(sch, cgroup_cancel_move) && p->scx.cgrp_moving_from) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_cancel_move, NULL, p, p->scx.cgrp_moving_from, css->cgroup); p->scx.cgrp_moving_from = NULL; } } void scx_group_set_weight(struct task_group *tg, unsigned long weight) { struct scx_sched *sch = scx_root; percpu_down_read(&scx_cgroup_ops_rwsem); if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_weight) && tg->scx.weight != weight) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_weight, NULL, tg_cgrp(tg), weight); tg->scx.weight = weight; percpu_up_read(&scx_cgroup_ops_rwsem); } void scx_group_set_idle(struct task_group *tg, bool idle) { struct scx_sched *sch = scx_root; percpu_down_read(&scx_cgroup_ops_rwsem); if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_idle)) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_idle, NULL, tg_cgrp(tg), idle); /* Update the task group's idle state */ tg->scx.idle = idle; percpu_up_read(&scx_cgroup_ops_rwsem); } void scx_group_set_bandwidth(struct task_group *tg, u64 period_us, u64 quota_us, u64 burst_us) { struct scx_sched *sch = scx_root; percpu_down_read(&scx_cgroup_ops_rwsem); if (scx_cgroup_enabled && SCX_HAS_OP(sch, cgroup_set_bandwidth) && (tg->scx.bw_period_us != period_us || tg->scx.bw_quota_us != quota_us || tg->scx.bw_burst_us != burst_us)) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_set_bandwidth, NULL, tg_cgrp(tg), period_us, quota_us, burst_us); tg->scx.bw_period_us = period_us; tg->scx.bw_quota_us = quota_us; tg->scx.bw_burst_us = burst_us; percpu_up_read(&scx_cgroup_ops_rwsem); } #endif /* CONFIG_EXT_GROUP_SCHED */ #if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED) static struct cgroup *root_cgroup(void) { return &cgrp_dfl_root.cgrp; } static struct cgroup *sch_cgroup(struct scx_sched *sch) { return sch->cgrp; } /* for each descendant of @cgrp including self, set ->scx_sched to @sch */ static void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) { struct cgroup *pos; struct cgroup_subsys_state *css; cgroup_for_each_live_descendant_pre(pos, css, cgrp) rcu_assign_pointer(pos->scx_sched, sch); } static void scx_cgroup_lock(void) { #ifdef CONFIG_EXT_GROUP_SCHED percpu_down_write(&scx_cgroup_ops_rwsem); #endif cgroup_lock(); } static void scx_cgroup_unlock(void) { cgroup_unlock(); #ifdef CONFIG_EXT_GROUP_SCHED percpu_up_write(&scx_cgroup_ops_rwsem); #endif } #else /* CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED */ static struct cgroup *root_cgroup(void) { return NULL; } static struct cgroup *sch_cgroup(struct scx_sched *sch) { return NULL; } static void set_cgroup_sched(struct cgroup *cgrp, struct scx_sched *sch) {} static void scx_cgroup_lock(void) {} static void scx_cgroup_unlock(void) {} #endif /* CONFIG_EXT_GROUP_SCHED || CONFIG_EXT_SUB_SCHED */ /* * Omitted operations: * * - migrate_task_rq: Unnecessary as task to cpu mapping is transient. * * - task_fork/dead: We need fork/dead notifications for all tasks regardless of * their current sched_class. Call them directly from sched core instead. */ DEFINE_SCHED_CLASS(ext) = { .enqueue_task = enqueue_task_scx, .dequeue_task = dequeue_task_scx, .yield_task = yield_task_scx, .yield_to_task = yield_to_task_scx, .wakeup_preempt = wakeup_preempt_scx, .pick_task = pick_task_scx, .put_prev_task = put_prev_task_scx, .set_next_task = set_next_task_scx, .select_task_rq = select_task_rq_scx, .task_woken = task_woken_scx, .set_cpus_allowed = set_cpus_allowed_scx, .rq_online = rq_online_scx, .rq_offline = rq_offline_scx, .task_tick = task_tick_scx, .switching_to = switching_to_scx, .switched_from = switched_from_scx, .switched_to = switched_to_scx, .reweight_task = reweight_task_scx, .prio_changed = prio_changed_scx, .update_curr = update_curr_scx, #ifdef CONFIG_UCLAMP_TASK .uclamp_enabled = 1, #endif }; static s32 init_dsq(struct scx_dispatch_q *dsq, u64 dsq_id, struct scx_sched *sch) { s32 cpu; memset(dsq, 0, sizeof(*dsq)); raw_spin_lock_init(&dsq->lock); INIT_LIST_HEAD(&dsq->list); dsq->id = dsq_id; dsq->sched = sch; dsq->pcpu = alloc_percpu(struct scx_dsq_pcpu); if (!dsq->pcpu) return -ENOMEM; for_each_possible_cpu(cpu) { struct scx_dsq_pcpu *pcpu = per_cpu_ptr(dsq->pcpu, cpu); pcpu->dsq = dsq; INIT_LIST_HEAD(&pcpu->deferred_reenq_user.node); } return 0; } static void exit_dsq(struct scx_dispatch_q *dsq) { s32 cpu; for_each_possible_cpu(cpu) { struct scx_dsq_pcpu *pcpu = per_cpu_ptr(dsq->pcpu, cpu); struct scx_deferred_reenq_user *dru = &pcpu->deferred_reenq_user; struct rq *rq = cpu_rq(cpu); /* * There must have been a RCU grace period since the last * insertion and @dsq should be off the deferred list by now. */ if (WARN_ON_ONCE(!list_empty(&dru->node))) { guard(raw_spinlock_irqsave)(&rq->scx.deferred_reenq_lock); list_del_init(&dru->node); } } free_percpu(dsq->pcpu); } static void free_dsq_rcufn(struct rcu_head *rcu) { struct scx_dispatch_q *dsq = container_of(rcu, struct scx_dispatch_q, rcu); exit_dsq(dsq); kfree(dsq); } static void free_dsq_irq_workfn(struct irq_work *irq_work) { struct llist_node *to_free = llist_del_all(&dsqs_to_free); struct scx_dispatch_q *dsq, *tmp_dsq; llist_for_each_entry_safe(dsq, tmp_dsq, to_free, free_node) call_rcu(&dsq->rcu, free_dsq_rcufn); } static DEFINE_IRQ_WORK(free_dsq_irq_work, free_dsq_irq_workfn); static void destroy_dsq(struct scx_sched *sch, u64 dsq_id) { struct scx_dispatch_q *dsq; unsigned long flags; rcu_read_lock(); dsq = find_user_dsq(sch, dsq_id); if (!dsq) goto out_unlock_rcu; raw_spin_lock_irqsave(&dsq->lock, flags); if (dsq->nr) { scx_error(sch, "attempting to destroy in-use dsq 0x%016llx (nr=%u)", dsq->id, dsq->nr); goto out_unlock_dsq; } if (rhashtable_remove_fast(&sch->dsq_hash, &dsq->hash_node, dsq_hash_params)) goto out_unlock_dsq; /* * Mark dead by invalidating ->id to prevent dispatch_enqueue() from * queueing more tasks. As this function can be called from anywhere, * freeing is bounced through an irq work to avoid nesting RCU * operations inside scheduler locks. */ dsq->id = SCX_DSQ_INVALID; if (llist_add(&dsq->free_node, &dsqs_to_free)) irq_work_queue(&free_dsq_irq_work); out_unlock_dsq: raw_spin_unlock_irqrestore(&dsq->lock, flags); out_unlock_rcu: rcu_read_unlock(); } #ifdef CONFIG_EXT_GROUP_SCHED static void scx_cgroup_exit(struct scx_sched *sch) { struct cgroup_subsys_state *css; scx_cgroup_enabled = false; /* * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk * cgroups and exit all the inited ones, all online cgroups are exited. */ css_for_each_descendant_post(css, &root_task_group.css) { struct task_group *tg = css_tg(css); if (!(tg->scx.flags & SCX_TG_INITED)) continue; tg->scx.flags &= ~SCX_TG_INITED; if (!sch->ops.cgroup_exit) continue; SCX_CALL_OP(sch, SCX_KF_UNLOCKED, cgroup_exit, NULL, css->cgroup); } } static int scx_cgroup_init(struct scx_sched *sch) { struct cgroup_subsys_state *css; int ret; /* * scx_tg_on/offline() are excluded through cgroup_lock(). If we walk * cgroups and init, all online cgroups are initialized. */ css_for_each_descendant_pre(css, &root_task_group.css) { struct task_group *tg = css_tg(css); struct scx_cgroup_init_args args = { .weight = tg->scx.weight, .bw_period_us = tg->scx.bw_period_us, .bw_quota_us = tg->scx.bw_quota_us, .bw_burst_us = tg->scx.bw_burst_us, }; if ((tg->scx.flags & (SCX_TG_ONLINE | SCX_TG_INITED)) != SCX_TG_ONLINE) continue; if (!sch->ops.cgroup_init) { tg->scx.flags |= SCX_TG_INITED; continue; } ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, cgroup_init, NULL, css->cgroup, &args); if (ret) { scx_error(sch, "ops.cgroup_init() failed (%d)", ret); return ret; } tg->scx.flags |= SCX_TG_INITED; } WARN_ON_ONCE(scx_cgroup_enabled); scx_cgroup_enabled = true; return 0; } #else static void scx_cgroup_exit(struct scx_sched *sch) {} static int scx_cgroup_init(struct scx_sched *sch) { return 0; } #endif /******************************************************************************** * Sysfs interface and ops enable/disable. */ #define SCX_ATTR(_name) \ static struct kobj_attribute scx_attr_##_name = { \ .attr = { .name = __stringify(_name), .mode = 0444 }, \ .show = scx_attr_##_name##_show, \ } static ssize_t scx_attr_state_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%s\n", scx_enable_state_str[scx_enable_state()]); } SCX_ATTR(state); static ssize_t scx_attr_switch_all_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%d\n", READ_ONCE(scx_switching_all)); } SCX_ATTR(switch_all); static ssize_t scx_attr_nr_rejected_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_nr_rejected)); } SCX_ATTR(nr_rejected); static ssize_t scx_attr_hotplug_seq_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_hotplug_seq)); } SCX_ATTR(hotplug_seq); static ssize_t scx_attr_enable_seq_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { return sysfs_emit(buf, "%ld\n", atomic_long_read(&scx_enable_seq)); } SCX_ATTR(enable_seq); static struct attribute *scx_global_attrs[] = { &scx_attr_state.attr, &scx_attr_switch_all.attr, &scx_attr_nr_rejected.attr, &scx_attr_hotplug_seq.attr, &scx_attr_enable_seq.attr, NULL, }; static const struct attribute_group scx_global_attr_group = { .attrs = scx_global_attrs, }; static void free_pnode(struct scx_sched_pnode *pnode); static void free_exit_info(struct scx_exit_info *ei); static void scx_sched_free_rcu_work(struct work_struct *work) { struct rcu_work *rcu_work = to_rcu_work(work); struct scx_sched *sch = container_of(rcu_work, struct scx_sched, rcu_work); struct rhashtable_iter rht_iter; struct scx_dispatch_q *dsq; int cpu, node; irq_work_sync(&sch->disable_irq_work); kthread_destroy_worker(sch->helper); timer_shutdown_sync(&sch->bypass_lb_timer); #ifdef CONFIG_EXT_SUB_SCHED kfree(sch->cgrp_path); if (sch_cgroup(sch)) cgroup_put(sch_cgroup(sch)); #endif /* CONFIG_EXT_SUB_SCHED */ for_each_possible_cpu(cpu) { struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); /* * $sch would have entered bypass mode before the RCU grace * period. As that blocks new deferrals, all * deferred_reenq_local_node's must be off-list by now. */ WARN_ON_ONCE(!list_empty(&pcpu->deferred_reenq_local.node)); exit_dsq(bypass_dsq(sch, cpu)); } free_percpu(sch->pcpu); for_each_node_state(node, N_POSSIBLE) free_pnode(sch->pnode[node]); kfree(sch->pnode); rhashtable_walk_enter(&sch->dsq_hash, &rht_iter); do { rhashtable_walk_start(&rht_iter); while (!IS_ERR_OR_NULL((dsq = rhashtable_walk_next(&rht_iter)))) destroy_dsq(sch, dsq->id); rhashtable_walk_stop(&rht_iter); } while (dsq == ERR_PTR(-EAGAIN)); rhashtable_walk_exit(&rht_iter); rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); free_exit_info(sch->exit_info); kfree(sch); } static void scx_kobj_release(struct kobject *kobj) { struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); INIT_RCU_WORK(&sch->rcu_work, scx_sched_free_rcu_work); queue_rcu_work(system_dfl_wq, &sch->rcu_work); } static ssize_t scx_attr_ops_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); return sysfs_emit(buf, "%s\n", sch->ops.name); } SCX_ATTR(ops); #define scx_attr_event_show(buf, at, events, kind) ({ \ sysfs_emit_at(buf, at, "%s %llu\n", #kind, (events)->kind); \ }) static ssize_t scx_attr_events_show(struct kobject *kobj, struct kobj_attribute *ka, char *buf) { struct scx_sched *sch = container_of(kobj, struct scx_sched, kobj); struct scx_event_stats events; int at = 0; scx_read_events(sch, &events); at += scx_attr_event_show(buf, at, &events, SCX_EV_SELECT_CPU_FALLBACK); at += scx_attr_event_show(buf, at, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE); at += scx_attr_event_show(buf, at, &events, SCX_EV_DISPATCH_KEEP_LAST); at += scx_attr_event_show(buf, at, &events, SCX_EV_ENQ_SKIP_EXITING); at += scx_attr_event_show(buf, at, &events, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED); at += scx_attr_event_show(buf, at, &events, SCX_EV_REENQ_IMMED); at += scx_attr_event_show(buf, at, &events, SCX_EV_REENQ_LOCAL_REPEAT); at += scx_attr_event_show(buf, at, &events, SCX_EV_REFILL_SLICE_DFL); at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_DURATION); at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_DISPATCH); at += scx_attr_event_show(buf, at, &events, SCX_EV_BYPASS_ACTIVATE); at += scx_attr_event_show(buf, at, &events, SCX_EV_INSERT_NOT_OWNED); at += scx_attr_event_show(buf, at, &events, SCX_EV_SUB_BYPASS_DISPATCH); return at; } SCX_ATTR(events); static struct attribute *scx_sched_attrs[] = { &scx_attr_ops.attr, &scx_attr_events.attr, NULL, }; ATTRIBUTE_GROUPS(scx_sched); static const struct kobj_type scx_ktype = { .release = scx_kobj_release, .sysfs_ops = &kobj_sysfs_ops, .default_groups = scx_sched_groups, }; static int scx_uevent(const struct kobject *kobj, struct kobj_uevent_env *env) { const struct scx_sched *sch; /* * scx_uevent() can be reached by both scx_sched kobjects (scx_ktype) * and sub-scheduler kset kobjects (kset_ktype) through the parent * chain walk. Filter out the latter to avoid invalid casts. */ if (kobj->ktype != &scx_ktype) return 0; sch = container_of(kobj, struct scx_sched, kobj); return add_uevent_var(env, "SCXOPS=%s", sch->ops.name); } static const struct kset_uevent_ops scx_uevent_ops = { .uevent = scx_uevent, }; /* * Used by sched_fork() and __setscheduler_prio() to pick the matching * sched_class. dl/rt are already handled. */ bool task_should_scx(int policy) { if (!scx_enabled() || unlikely(scx_enable_state() == SCX_DISABLING)) return false; if (READ_ONCE(scx_switching_all)) return true; return policy == SCHED_EXT; } bool scx_allow_ttwu_queue(const struct task_struct *p) { struct scx_sched *sch; if (!scx_enabled()) return true; sch = scx_task_sched(p); if (unlikely(!sch)) return true; if (sch->ops.flags & SCX_OPS_ALLOW_QUEUED_WAKEUP) return true; if (unlikely(p->sched_class != &ext_sched_class)) return true; return false; } /** * handle_lockup - sched_ext common lockup handler * @fmt: format string * * Called on system stall or lockup condition and initiates abort of sched_ext * if enabled, which may resolve the reported lockup. * * Returns %true if sched_ext is enabled and abort was initiated, which may * resolve the lockup. %false if sched_ext is not enabled or abort was already * initiated by someone else. */ static __printf(1, 2) bool handle_lockup(const char *fmt, ...) { struct scx_sched *sch; va_list args; bool ret; guard(rcu)(); sch = rcu_dereference(scx_root); if (unlikely(!sch)) return false; switch (scx_enable_state()) { case SCX_ENABLING: case SCX_ENABLED: va_start(args, fmt); ret = scx_verror(sch, fmt, args); va_end(args); return ret; default: return false; } } /** * scx_rcu_cpu_stall - sched_ext RCU CPU stall handler * * While there are various reasons why RCU CPU stalls can occur on a system * that may not be caused by the current BPF scheduler, try kicking out the * current scheduler in an attempt to recover the system to a good state before * issuing panics. * * Returns %true if sched_ext is enabled and abort was initiated, which may * resolve the reported RCU stall. %false if sched_ext is not enabled or someone * else already initiated abort. */ bool scx_rcu_cpu_stall(void) { return handle_lockup("RCU CPU stall detected!"); } /** * scx_softlockup - sched_ext softlockup handler * @dur_s: number of seconds of CPU stuck due to soft lockup * * On some multi-socket setups (e.g. 2x Intel 8480c), the BPF scheduler can * live-lock the system by making many CPUs target the same DSQ to the point * where soft-lockup detection triggers. This function is called from * soft-lockup watchdog when the triggering point is close and tries to unjam * the system and aborting the BPF scheduler. */ void scx_softlockup(u32 dur_s) { if (!handle_lockup("soft lockup - CPU %d stuck for %us", smp_processor_id(), dur_s)) return; printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU %d stuck for %us, disabling BPF scheduler\n", smp_processor_id(), dur_s); } /** * scx_hardlockup - sched_ext hardlockup handler * * A poorly behaving BPF scheduler can trigger hard lockup by e.g. putting * numerous affinitized tasks in a single queue and directing all CPUs at it. * Try kicking out the current scheduler in an attempt to recover the system to * a good state before taking more drastic actions. * * Returns %true if sched_ext is enabled and abort was initiated, which may * resolve the reported hardlockup. %false if sched_ext is not enabled or * someone else already initiated abort. */ bool scx_hardlockup(int cpu) { if (!handle_lockup("hard lockup - CPU %d", cpu)) return false; printk_deferred(KERN_ERR "sched_ext: Hard lockup - CPU %d, disabling BPF scheduler\n", cpu); return true; } static u32 bypass_lb_cpu(struct scx_sched *sch, s32 donor, struct cpumask *donee_mask, struct cpumask *resched_mask, u32 nr_donor_target, u32 nr_donee_target) { struct rq *donor_rq = cpu_rq(donor); struct scx_dispatch_q *donor_dsq = bypass_dsq(sch, donor); struct task_struct *p, *n; struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, donor_dsq, 0); s32 delta = READ_ONCE(donor_dsq->nr) - nr_donor_target; u32 nr_balanced = 0, min_delta_us; /* * All we want to guarantee is reasonable forward progress. No reason to * fine tune. Assuming every task on @donor_dsq runs their full slice, * consider offloading iff the total queued duration is over the * threshold. */ min_delta_us = READ_ONCE(scx_bypass_lb_intv_us) / SCX_BYPASS_LB_MIN_DELTA_DIV; if (delta < DIV_ROUND_UP(min_delta_us, READ_ONCE(scx_slice_bypass_us))) return 0; raw_spin_rq_lock_irq(donor_rq); raw_spin_lock(&donor_dsq->lock); list_add(&cursor.node, &donor_dsq->list); resume: n = container_of(&cursor, struct task_struct, scx.dsq_list); n = nldsq_next_task(donor_dsq, n, false); while ((p = n)) { struct scx_dispatch_q *donee_dsq; int donee; n = nldsq_next_task(donor_dsq, n, false); if (donor_dsq->nr <= nr_donor_target) break; if (cpumask_empty(donee_mask)) break; donee = cpumask_any_and_distribute(donee_mask, p->cpus_ptr); if (donee >= nr_cpu_ids) continue; donee_dsq = bypass_dsq(sch, donee); /* * $p's rq is not locked but $p's DSQ lock protects its * scheduling properties making this test safe. */ if (!task_can_run_on_remote_rq(sch, p, cpu_rq(donee), false)) continue; /* * Moving $p from one non-local DSQ to another. The source rq * and DSQ are already locked. Do an abbreviated dequeue and * then perform enqueue without unlocking $donor_dsq. * * We don't want to drop and reacquire the lock on each * iteration as @donor_dsq can be very long and potentially * highly contended. Donee DSQs are less likely to be contended. * The nested locking is safe as only this LB moves tasks * between bypass DSQs. */ dispatch_dequeue_locked(p, donor_dsq); dispatch_enqueue(sch, cpu_rq(donee), donee_dsq, p, SCX_ENQ_NESTED); /* * $donee might have been idle and need to be woken up. No need * to be clever. Kick every CPU that receives tasks. */ cpumask_set_cpu(donee, resched_mask); if (READ_ONCE(donee_dsq->nr) >= nr_donee_target) cpumask_clear_cpu(donee, donee_mask); nr_balanced++; if (!(nr_balanced % SCX_BYPASS_LB_BATCH) && n) { list_move_tail(&cursor.node, &n->scx.dsq_list.node); raw_spin_unlock(&donor_dsq->lock); raw_spin_rq_unlock_irq(donor_rq); cpu_relax(); raw_spin_rq_lock_irq(donor_rq); raw_spin_lock(&donor_dsq->lock); goto resume; } } list_del_init(&cursor.node); raw_spin_unlock(&donor_dsq->lock); raw_spin_rq_unlock_irq(donor_rq); return nr_balanced; } static void bypass_lb_node(struct scx_sched *sch, int node) { const struct cpumask *node_mask = cpumask_of_node(node); struct cpumask *donee_mask = scx_bypass_lb_donee_cpumask; struct cpumask *resched_mask = scx_bypass_lb_resched_cpumask; u32 nr_tasks = 0, nr_cpus = 0, nr_balanced = 0; u32 nr_target, nr_donor_target; u32 before_min = U32_MAX, before_max = 0; u32 after_min = U32_MAX, after_max = 0; int cpu; /* count the target tasks and CPUs */ for_each_cpu_and(cpu, cpu_online_mask, node_mask) { u32 nr = READ_ONCE(bypass_dsq(sch, cpu)->nr); nr_tasks += nr; nr_cpus++; before_min = min(nr, before_min); before_max = max(nr, before_max); } if (!nr_cpus) return; /* * We don't want CPUs to have more than $nr_donor_target tasks and * balancing to fill donee CPUs upto $nr_target. Once targets are * calculated, find the donee CPUs. */ nr_target = DIV_ROUND_UP(nr_tasks, nr_cpus); nr_donor_target = DIV_ROUND_UP(nr_target * SCX_BYPASS_LB_DONOR_PCT, 100); cpumask_clear(donee_mask); for_each_cpu_and(cpu, cpu_online_mask, node_mask) { if (READ_ONCE(bypass_dsq(sch, cpu)->nr) < nr_target) cpumask_set_cpu(cpu, donee_mask); } /* iterate !donee CPUs and see if they should be offloaded */ cpumask_clear(resched_mask); for_each_cpu_and(cpu, cpu_online_mask, node_mask) { if (cpumask_empty(donee_mask)) break; if (cpumask_test_cpu(cpu, donee_mask)) continue; if (READ_ONCE(bypass_dsq(sch, cpu)->nr) <= nr_donor_target) continue; nr_balanced += bypass_lb_cpu(sch, cpu, donee_mask, resched_mask, nr_donor_target, nr_target); } for_each_cpu(cpu, resched_mask) resched_cpu(cpu); for_each_cpu_and(cpu, cpu_online_mask, node_mask) { u32 nr = READ_ONCE(bypass_dsq(sch, cpu)->nr); after_min = min(nr, after_min); after_max = max(nr, after_max); } trace_sched_ext_bypass_lb(node, nr_cpus, nr_tasks, nr_balanced, before_min, before_max, after_min, after_max); } /* * In bypass mode, all tasks are put on the per-CPU bypass DSQs. If the machine * is over-saturated and the BPF scheduler skewed tasks into few CPUs, some * bypass DSQs can be overloaded. If there are enough tasks to saturate other * lightly loaded CPUs, such imbalance can lead to very high execution latency * on the overloaded CPUs and thus to hung tasks and RCU stalls. To avoid such * outcomes, a simple load balancing mechanism is implemented by the following * timer which runs periodically while bypass mode is in effect. */ static void scx_bypass_lb_timerfn(struct timer_list *timer) { struct scx_sched *sch = container_of(timer, struct scx_sched, bypass_lb_timer); int node; u32 intv_us; if (!bypass_dsp_enabled(sch)) return; for_each_node_with_cpus(node) bypass_lb_node(sch, node); intv_us = READ_ONCE(scx_bypass_lb_intv_us); if (intv_us) mod_timer(timer, jiffies + usecs_to_jiffies(intv_us)); } static bool inc_bypass_depth(struct scx_sched *sch) { lockdep_assert_held(&scx_bypass_lock); WARN_ON_ONCE(sch->bypass_depth < 0); WRITE_ONCE(sch->bypass_depth, sch->bypass_depth + 1); if (sch->bypass_depth != 1) return false; WRITE_ONCE(sch->slice_dfl, READ_ONCE(scx_slice_bypass_us) * NSEC_PER_USEC); sch->bypass_timestamp = ktime_get_ns(); scx_add_event(sch, SCX_EV_BYPASS_ACTIVATE, 1); return true; } static bool dec_bypass_depth(struct scx_sched *sch) { lockdep_assert_held(&scx_bypass_lock); WARN_ON_ONCE(sch->bypass_depth < 1); WRITE_ONCE(sch->bypass_depth, sch->bypass_depth - 1); if (sch->bypass_depth != 0) return false; WRITE_ONCE(sch->slice_dfl, SCX_SLICE_DFL); scx_add_event(sch, SCX_EV_BYPASS_DURATION, ktime_get_ns() - sch->bypass_timestamp); return true; } static void enable_bypass_dsp(struct scx_sched *sch) { struct scx_sched *host = scx_parent(sch) ?: sch; u32 intv_us = READ_ONCE(scx_bypass_lb_intv_us); s32 ret; /* * @sch->bypass_depth transitioning from 0 to 1 triggers enabling. * Shouldn't stagger. */ if (WARN_ON_ONCE(test_and_set_bit(0, &sch->bypass_dsp_claim))) return; /* * When a sub-sched bypasses, its tasks are queued on the bypass DSQs of * the nearest non-bypassing ancestor or root. As enable_bypass_dsp() is * called iff @sch is not already bypassed due to an ancestor bypassing, * we can assume that the parent is not bypassing and thus will be the * host of the bypass DSQs. * * While the situation may change in the future, the following * guarantees that the nearest non-bypassing ancestor or root has bypass * dispatch enabled while a descendant is bypassing, which is all that's * required. * * bypass_dsp_enabled() test is used to determine whether to enter the * bypass dispatch handling path from both bypassing and hosting scheds. * Bump enable depth on both @sch and bypass dispatch host. */ ret = atomic_inc_return(&sch->bypass_dsp_enable_depth); WARN_ON_ONCE(ret <= 0); if (host != sch) { ret = atomic_inc_return(&host->bypass_dsp_enable_depth); WARN_ON_ONCE(ret <= 0); } /* * The LB timer will stop running if bypass dispatch is disabled. Start * after enabling bypass dispatch. */ if (intv_us && !timer_pending(&host->bypass_lb_timer)) mod_timer(&host->bypass_lb_timer, jiffies + usecs_to_jiffies(intv_us)); } /* may be called without holding scx_bypass_lock */ static void disable_bypass_dsp(struct scx_sched *sch) { s32 ret; if (!test_and_clear_bit(0, &sch->bypass_dsp_claim)) return; ret = atomic_dec_return(&sch->bypass_dsp_enable_depth); WARN_ON_ONCE(ret < 0); if (scx_parent(sch)) { ret = atomic_dec_return(&scx_parent(sch)->bypass_dsp_enable_depth); WARN_ON_ONCE(ret < 0); } } /** * scx_bypass - [Un]bypass scx_ops and guarantee forward progress * @sch: sched to bypass * @bypass: true for bypass, false for unbypass * * Bypassing guarantees that all runnable tasks make forward progress without * trusting the BPF scheduler. We can't grab any mutexes or rwsems as they might * be held by tasks that the BPF scheduler is forgetting to run, which * unfortunately also excludes toggling the static branches. * * Let's work around by overriding a couple ops and modifying behaviors based on * the DISABLING state and then cycling the queued tasks through dequeue/enqueue * to force global FIFO scheduling. * * - ops.select_cpu() is ignored and the default select_cpu() is used. * * - ops.enqueue() is ignored and tasks are queued in simple global FIFO order. * %SCX_OPS_ENQ_LAST is also ignored. * * - ops.dispatch() is ignored. * * - balance_one() does not set %SCX_RQ_BAL_KEEP on non-zero slice as slice * can't be trusted. Whenever a tick triggers, the running task is rotated to * the tail of the queue with core_sched_at touched. * * - pick_next_task() suppresses zero slice warning. * * - scx_kick_cpu() is disabled to avoid irq_work malfunction during PM * operations. * * - scx_prio_less() reverts to the default core_sched_at order. */ static void scx_bypass(struct scx_sched *sch, bool bypass) { struct scx_sched *pos; unsigned long flags; int cpu; raw_spin_lock_irqsave(&scx_bypass_lock, flags); if (bypass) { if (!inc_bypass_depth(sch)) goto unlock; enable_bypass_dsp(sch); } else { if (!dec_bypass_depth(sch)) goto unlock; } /* * Bypass state is propagated to all descendants - an scx_sched bypasses * if itself or any of its ancestors are in bypass mode. */ raw_spin_lock(&scx_sched_lock); scx_for_each_descendant_pre(pos, sch) { if (pos == sch) continue; if (bypass) inc_bypass_depth(pos); else dec_bypass_depth(pos); } raw_spin_unlock(&scx_sched_lock); /* * No task property is changing. We just need to make sure all currently * queued tasks are re-queued according to the new scx_bypassing() * state. As an optimization, walk each rq's runnable_list instead of * the scx_tasks list. * * This function can't trust the scheduler and thus can't use * cpus_read_lock(). Walk all possible CPUs instead of online. */ for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); struct task_struct *p, *n; raw_spin_rq_lock(rq); raw_spin_lock(&scx_sched_lock); scx_for_each_descendant_pre(pos, sch) { struct scx_sched_pcpu *pcpu = per_cpu_ptr(pos->pcpu, cpu); if (pos->bypass_depth) pcpu->flags |= SCX_SCHED_PCPU_BYPASSING; else pcpu->flags &= ~SCX_SCHED_PCPU_BYPASSING; } raw_spin_unlock(&scx_sched_lock); /* * We need to guarantee that no tasks are on the BPF scheduler * while bypassing. Either we see enabled or the enable path * sees scx_bypassing() before moving tasks to SCX. */ if (!scx_enabled()) { raw_spin_rq_unlock(rq); continue; } /* * The use of list_for_each_entry_safe_reverse() is required * because each task is going to be removed from and added back * to the runnable_list during iteration. Because they're added * to the tail of the list, safe reverse iteration can still * visit all nodes. */ list_for_each_entry_safe_reverse(p, n, &rq->scx.runnable_list, scx.runnable_node) { if (!scx_is_descendant(scx_task_sched(p), sch)) continue; /* cycling deq/enq is enough, see the function comment */ scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) { /* nothing */ ; } } /* resched to restore ticks and idle state */ if (cpu_online(cpu) || cpu == smp_processor_id()) resched_curr(rq); raw_spin_rq_unlock(rq); } /* disarming must come after moving all tasks out of the bypass DSQs */ if (!bypass) disable_bypass_dsp(sch); unlock: raw_spin_unlock_irqrestore(&scx_bypass_lock, flags); } static void free_exit_info(struct scx_exit_info *ei) { kvfree(ei->dump); kfree(ei->msg); kfree(ei->bt); kfree(ei); } static struct scx_exit_info *alloc_exit_info(size_t exit_dump_len) { struct scx_exit_info *ei; ei = kzalloc_obj(*ei); if (!ei) return NULL; ei->bt = kzalloc_objs(ei->bt[0], SCX_EXIT_BT_LEN); ei->msg = kzalloc(SCX_EXIT_MSG_LEN, GFP_KERNEL); ei->dump = kvzalloc(exit_dump_len, GFP_KERNEL); if (!ei->bt || !ei->msg || !ei->dump) { free_exit_info(ei); return NULL; } return ei; } static const char *scx_exit_reason(enum scx_exit_kind kind) { switch (kind) { case SCX_EXIT_UNREG: return "unregistered from user space"; case SCX_EXIT_UNREG_BPF: return "unregistered from BPF"; case SCX_EXIT_UNREG_KERN: return "unregistered from the main kernel"; case SCX_EXIT_SYSRQ: return "disabled by sysrq-S"; case SCX_EXIT_PARENT: return "parent exiting"; case SCX_EXIT_ERROR: return "runtime error"; case SCX_EXIT_ERROR_BPF: return "scx_bpf_error"; case SCX_EXIT_ERROR_STALL: return "runnable task stall"; default: return ""; } } static void free_kick_syncs(void) { int cpu; for_each_possible_cpu(cpu) { struct scx_kick_syncs **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu); struct scx_kick_syncs *to_free; to_free = rcu_replace_pointer(*ksyncs, NULL, true); if (to_free) kvfree_rcu(to_free, rcu); } } static void refresh_watchdog(void) { struct scx_sched *sch; unsigned long intv = ULONG_MAX; /* take the shortest timeout and use its half for watchdog interval */ rcu_read_lock(); list_for_each_entry_rcu(sch, &scx_sched_all, all) intv = max(min(intv, sch->watchdog_timeout / 2), 1); rcu_read_unlock(); WRITE_ONCE(scx_watchdog_timestamp, jiffies); WRITE_ONCE(scx_watchdog_interval, intv); if (intv < ULONG_MAX) mod_delayed_work(system_dfl_wq, &scx_watchdog_work, intv); else cancel_delayed_work_sync(&scx_watchdog_work); } static s32 scx_link_sched(struct scx_sched *sch) { scoped_guard(raw_spinlock_irq, &scx_sched_lock) { #ifdef CONFIG_EXT_SUB_SCHED struct scx_sched *parent = scx_parent(sch); s32 ret; if (parent) { /* * scx_claim_exit() propagates exit_kind transition to * its sub-scheds while holding scx_sched_lock - either * we can see the parent's non-NONE exit_kind or the * parent can shoot us down. */ if (atomic_read(&parent->exit_kind) != SCX_EXIT_NONE) { scx_error(sch, "parent disabled"); return -ENOENT; } ret = rhashtable_lookup_insert_fast(&scx_sched_hash, &sch->hash_node, scx_sched_hash_params); if (ret) { scx_error(sch, "failed to insert into scx_sched_hash (%d)", ret); return ret; } list_add_tail(&sch->sibling, &parent->children); } #endif /* CONFIG_EXT_SUB_SCHED */ list_add_tail_rcu(&sch->all, &scx_sched_all); } refresh_watchdog(); return 0; } static void scx_unlink_sched(struct scx_sched *sch) { scoped_guard(raw_spinlock_irq, &scx_sched_lock) { #ifdef CONFIG_EXT_SUB_SCHED if (scx_parent(sch)) { rhashtable_remove_fast(&scx_sched_hash, &sch->hash_node, scx_sched_hash_params); list_del_init(&sch->sibling); } #endif /* CONFIG_EXT_SUB_SCHED */ list_del_rcu(&sch->all); } refresh_watchdog(); } /* * Called to disable future dumps and wait for in-progress one while disabling * @sch. Once @sch becomes empty during disable, there's no point in dumping it. * This prevents calling dump ops on a dead sch. */ static void scx_disable_dump(struct scx_sched *sch) { guard(raw_spinlock_irqsave)(&scx_dump_lock); sch->dump_disabled = true; } #ifdef CONFIG_EXT_SUB_SCHED static DECLARE_WAIT_QUEUE_HEAD(scx_unlink_waitq); static void drain_descendants(struct scx_sched *sch) { /* * Child scheds that finished the critical part of disabling will take * themselves off @sch->children. Wait for it to drain. As propagation * is recursive, empty @sch->children means that all proper descendant * scheds reached unlinking stage. */ wait_event(scx_unlink_waitq, list_empty(&sch->children)); } static void scx_fail_parent(struct scx_sched *sch, struct task_struct *failed, s32 fail_code) { struct scx_sched *parent = scx_parent(sch); struct scx_task_iter sti; struct task_struct *p; scx_error(parent, "ops.init_task() failed (%d) for %s[%d] while disabling a sub-scheduler", fail_code, failed->comm, failed->pid); /* * Once $parent is bypassed, it's safe to put SCX_TASK_NONE tasks into * it. This may cause downstream failures on the BPF side but $parent is * dying anyway. */ scx_bypass(parent, true); scx_task_iter_start(&sti, sch->cgrp); while ((p = scx_task_iter_next_locked(&sti))) { if (scx_task_on_sched(parent, p)) continue; scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) { scx_disable_and_exit_task(sch, p); rcu_assign_pointer(p->scx.sched, parent); } } scx_task_iter_stop(&sti); } static void scx_sub_disable(struct scx_sched *sch) { struct scx_sched *parent = scx_parent(sch); struct scx_task_iter sti; struct task_struct *p; int ret; /* * Guarantee forward progress and wait for descendants to be disabled. * To limit disruptions, $parent is not bypassed. Tasks are fully * prepped and then inserted back into $parent. */ scx_bypass(sch, true); drain_descendants(sch); /* * Here, every runnable task is guaranteed to make forward progress and * we can safely use blocking synchronization constructs. Actually * disable ops. */ mutex_lock(&scx_enable_mutex); percpu_down_write(&scx_fork_rwsem); scx_cgroup_lock(); set_cgroup_sched(sch_cgroup(sch), parent); scx_task_iter_start(&sti, sch->cgrp); while ((p = scx_task_iter_next_locked(&sti))) { struct rq *rq; struct rq_flags rf; /* filter out duplicate visits */ if (scx_task_on_sched(parent, p)) continue; /* * By the time control reaches here, all descendant schedulers * should already have been disabled. */ WARN_ON_ONCE(!scx_task_on_sched(sch, p)); /* * If $p is about to be freed, nothing prevents $sch from * unloading before $p reaches sched_ext_free(). Disable and * exit $p right away. */ if (!tryget_task_struct(p)) { scx_disable_and_exit_task(sch, p); continue; } scx_task_iter_unlock(&sti); /* * $p is READY or ENABLED on @sch. Initialize for $parent, * disable and exit from @sch, and then switch over to $parent. * * If a task fails to initialize for $parent, the only available * action is disabling $parent too. While this allows disabling * of a child sched to cause the parent scheduler to fail, the * failure can only originate from ops.init_task() of the * parent. A child can't directly affect the parent through its * own failures. */ ret = __scx_init_task(parent, p, false); if (ret) { scx_fail_parent(sch, p, ret); put_task_struct(p); break; } rq = task_rq_lock(p, &rf); scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) { /* * $p is initialized for $parent and still attached to * @sch. Disable and exit for @sch, switch over to * $parent, override the state to READY to account for * $p having already been initialized, and then enable. */ scx_disable_and_exit_task(sch, p); scx_set_task_state(p, SCX_TASK_INIT); rcu_assign_pointer(p->scx.sched, parent); scx_set_task_state(p, SCX_TASK_READY); scx_enable_task(parent, p); } task_rq_unlock(rq, p, &rf); put_task_struct(p); } scx_task_iter_stop(&sti); scx_disable_dump(sch); scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); /* * All tasks are moved off of @sch but there may still be on-going * operations (e.g. ops.select_cpu()). Drain them by flushing RCU. Use * the expedited version as ancestors may be waiting in bypass mode. * Also, tell the parent that there is no need to keep running bypass * DSQs for us. */ synchronize_rcu_expedited(); disable_bypass_dsp(sch); scx_unlink_sched(sch); mutex_unlock(&scx_enable_mutex); /* * @sch is now unlinked from the parent's children list. Notify and call * ops.sub_detach/exit(). Note that ops.sub_detach/exit() must be called * after unlinking and releasing all locks. See scx_claim_exit(). */ wake_up_all(&scx_unlink_waitq); if (parent->ops.sub_detach && sch->sub_attached) { struct scx_sub_detach_args sub_detach_args = { .ops = &sch->ops, .cgroup_path = sch->cgrp_path, }; SCX_CALL_OP(parent, SCX_KF_UNLOCKED, sub_detach, NULL, &sub_detach_args); } if (sch->ops.exit) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, exit, NULL, sch->exit_info); kobject_del(&sch->kobj); } #else /* CONFIG_EXT_SUB_SCHED */ static void drain_descendants(struct scx_sched *sch) { } static void scx_sub_disable(struct scx_sched *sch) { } #endif /* CONFIG_EXT_SUB_SCHED */ static void scx_root_disable(struct scx_sched *sch) { struct scx_exit_info *ei = sch->exit_info; struct scx_task_iter sti; struct task_struct *p; int cpu; /* guarantee forward progress and wait for descendants to be disabled */ scx_bypass(sch, true); drain_descendants(sch); switch (scx_set_enable_state(SCX_DISABLING)) { case SCX_DISABLING: WARN_ONCE(true, "sched_ext: duplicate disabling instance?"); break; case SCX_DISABLED: pr_warn("sched_ext: ops error detected without ops (%s)\n", sch->exit_info->msg); WARN_ON_ONCE(scx_set_enable_state(SCX_DISABLED) != SCX_DISABLING); goto done; default: break; } /* * Here, every runnable task is guaranteed to make forward progress and * we can safely use blocking synchronization constructs. Actually * disable ops. */ mutex_lock(&scx_enable_mutex); static_branch_disable(&__scx_switched_all); WRITE_ONCE(scx_switching_all, false); /* * Shut down cgroup support before tasks so that the cgroup attach path * doesn't race against scx_disable_and_exit_task(). */ scx_cgroup_lock(); scx_cgroup_exit(sch); scx_cgroup_unlock(); /* * The BPF scheduler is going away. All tasks including %TASK_DEAD ones * must be switched out and exited synchronously. */ percpu_down_write(&scx_fork_rwsem); scx_init_task_enabled = false; scx_task_iter_start(&sti, NULL); while ((p = scx_task_iter_next_locked(&sti))) { unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK; const struct sched_class *old_class = p->sched_class; const struct sched_class *new_class = scx_setscheduler_class(p); update_rq_clock(task_rq(p)); if (old_class != new_class) queue_flags |= DEQUEUE_CLASS; scoped_guard (sched_change, p, queue_flags) { p->sched_class = new_class; } scx_disable_and_exit_task(scx_task_sched(p), p); } scx_task_iter_stop(&sti); scx_disable_dump(sch); scx_cgroup_lock(); set_cgroup_sched(sch_cgroup(sch), NULL); scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); /* * Invalidate all the rq clocks to prevent getting outdated * rq clocks from a previous scx scheduler. */ for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); scx_rq_clock_invalidate(rq); } /* no task is on scx, turn off all the switches and flush in-progress calls */ static_branch_disable(&__scx_enabled); bitmap_zero(sch->has_op, SCX_OPI_END); scx_idle_disable(); synchronize_rcu(); if (ei->kind >= SCX_EXIT_ERROR) { pr_err("sched_ext: BPF scheduler \"%s\" disabled (%s)\n", sch->ops.name, ei->reason); if (ei->msg[0] != '\0') pr_err("sched_ext: %s: %s\n", sch->ops.name, ei->msg); #ifdef CONFIG_STACKTRACE stack_trace_print(ei->bt, ei->bt_len, 2); #endif } else { pr_info("sched_ext: BPF scheduler \"%s\" disabled (%s)\n", sch->ops.name, ei->reason); } if (sch->ops.exit) SCX_CALL_OP(sch, SCX_KF_UNLOCKED, exit, NULL, ei); scx_unlink_sched(sch); /* * scx_root clearing must be inside cpus_read_lock(). See * handle_hotplug(). */ cpus_read_lock(); RCU_INIT_POINTER(scx_root, NULL); cpus_read_unlock(); /* * Delete the kobject from the hierarchy synchronously. Otherwise, sysfs * could observe an object of the same name still in the hierarchy when * the next scheduler is loaded. */ kobject_del(&sch->kobj); free_kick_syncs(); mutex_unlock(&scx_enable_mutex); WARN_ON_ONCE(scx_set_enable_state(SCX_DISABLED) != SCX_DISABLING); done: scx_bypass(sch, false); } /* * Claim the exit on @sch. The caller must ensure that the helper kthread work * is kicked before the current task can be preempted. Once exit_kind is * claimed, scx_error() can no longer trigger, so if the current task gets * preempted and the BPF scheduler fails to schedule it back, the helper work * will never be kicked and the whole system can wedge. */ static bool scx_claim_exit(struct scx_sched *sch, enum scx_exit_kind kind) { int none = SCX_EXIT_NONE; lockdep_assert_preemption_disabled(); if (WARN_ON_ONCE(kind == SCX_EXIT_NONE || kind == SCX_EXIT_DONE)) kind = SCX_EXIT_ERROR; if (!atomic_try_cmpxchg(&sch->exit_kind, &none, kind)) return false; /* * Some CPUs may be trapped in the dispatch paths. Set the aborting * flag to break potential live-lock scenarios, ensuring we can * successfully reach scx_bypass(). */ WRITE_ONCE(sch->aborting, true); /* * Propagate exits to descendants immediately. Each has a dedicated * helper kthread and can run in parallel. While most of disabling is * serialized, running them in separate threads allows parallelizing * ops.exit(), which can take arbitrarily long prolonging bypass mode. * * To guarantee forward progress, this propagation must be in-line so * that ->aborting is synchronously asserted for all sub-scheds. The * propagation is also the interlocking point against sub-sched * attachment. See scx_link_sched(). * * This doesn't cause recursions as propagation only takes place for * non-propagation exits. */ if (kind != SCX_EXIT_PARENT) { scoped_guard (raw_spinlock_irqsave, &scx_sched_lock) { struct scx_sched *pos; scx_for_each_descendant_pre(pos, sch) scx_disable(pos, SCX_EXIT_PARENT); } } return true; } static void scx_disable_workfn(struct kthread_work *work) { struct scx_sched *sch = container_of(work, struct scx_sched, disable_work); struct scx_exit_info *ei = sch->exit_info; int kind; kind = atomic_read(&sch->exit_kind); while (true) { if (kind == SCX_EXIT_DONE) /* already disabled? */ return; WARN_ON_ONCE(kind == SCX_EXIT_NONE); if (atomic_try_cmpxchg(&sch->exit_kind, &kind, SCX_EXIT_DONE)) break; } ei->kind = kind; ei->reason = scx_exit_reason(ei->kind); if (scx_parent(sch)) scx_sub_disable(sch); else scx_root_disable(sch); } static void scx_disable(struct scx_sched *sch, enum scx_exit_kind kind) { guard(preempt)(); if (scx_claim_exit(sch, kind)) irq_work_queue(&sch->disable_irq_work); } static void dump_newline(struct seq_buf *s) { trace_sched_ext_dump(""); /* @s may be zero sized and seq_buf triggers WARN if so */ if (s->size) seq_buf_putc(s, '\n'); } static __printf(2, 3) void dump_line(struct seq_buf *s, const char *fmt, ...) { va_list args; #ifdef CONFIG_TRACEPOINTS if (trace_sched_ext_dump_enabled()) { /* protected by scx_dump_lock */ static char line_buf[SCX_EXIT_MSG_LEN]; va_start(args, fmt); vscnprintf(line_buf, sizeof(line_buf), fmt, args); va_end(args); trace_call__sched_ext_dump(line_buf); } #endif /* @s may be zero sized and seq_buf triggers WARN if so */ if (s->size) { va_start(args, fmt); seq_buf_vprintf(s, fmt, args); va_end(args); seq_buf_putc(s, '\n'); } } static void dump_stack_trace(struct seq_buf *s, const char *prefix, const unsigned long *bt, unsigned int len) { unsigned int i; for (i = 0; i < len; i++) dump_line(s, "%s%pS", prefix, (void *)bt[i]); } static void ops_dump_init(struct seq_buf *s, const char *prefix) { struct scx_dump_data *dd = &scx_dump_data; lockdep_assert_irqs_disabled(); dd->cpu = smp_processor_id(); /* allow scx_bpf_dump() */ dd->first = true; dd->cursor = 0; dd->s = s; dd->prefix = prefix; } static void ops_dump_flush(void) { struct scx_dump_data *dd = &scx_dump_data; char *line = dd->buf.line; if (!dd->cursor) return; /* * There's something to flush and this is the first line. Insert a blank * line to distinguish ops dump. */ if (dd->first) { dump_newline(dd->s); dd->first = false; } /* * There may be multiple lines in $line. Scan and emit each line * separately. */ while (true) { char *end = line; char c; while (*end != '\n' && *end != '\0') end++; /* * If $line overflowed, it may not have newline at the end. * Always emit with a newline. */ c = *end; *end = '\0'; dump_line(dd->s, "%s%s", dd->prefix, line); if (c == '\0') break; /* move to the next line */ end++; if (*end == '\0') break; line = end; } dd->cursor = 0; } static void ops_dump_exit(void) { ops_dump_flush(); scx_dump_data.cpu = -1; } static void scx_dump_task(struct scx_sched *sch, struct seq_buf *s, struct scx_dump_ctx *dctx, struct task_struct *p, char marker) { static unsigned long bt[SCX_EXIT_BT_LEN]; struct scx_sched *task_sch = scx_task_sched(p); const char *own_marker; char sch_id_buf[32]; char dsq_id_buf[19] = "(n/a)"; unsigned long ops_state = atomic_long_read(&p->scx.ops_state); unsigned int bt_len = 0; own_marker = task_sch == sch ? "*" : ""; if (task_sch->level == 0) scnprintf(sch_id_buf, sizeof(sch_id_buf), "root"); else scnprintf(sch_id_buf, sizeof(sch_id_buf), "sub%d-%llu", task_sch->level, task_sch->ops.sub_cgroup_id); if (p->scx.dsq) scnprintf(dsq_id_buf, sizeof(dsq_id_buf), "0x%llx", (unsigned long long)p->scx.dsq->id); dump_newline(s); dump_line(s, " %c%c %s[%d] %s%s %+ldms", marker, task_state_to_char(p), p->comm, p->pid, own_marker, sch_id_buf, jiffies_delta_msecs(p->scx.runnable_at, dctx->at_jiffies)); dump_line(s, " scx_state/flags=%u/0x%x dsq_flags=0x%x ops_state/qseq=%lu/%lu", scx_get_task_state(p) >> SCX_TASK_STATE_SHIFT, p->scx.flags & ~SCX_TASK_STATE_MASK, p->scx.dsq_flags, ops_state & SCX_OPSS_STATE_MASK, ops_state >> SCX_OPSS_QSEQ_SHIFT); dump_line(s, " sticky/holding_cpu=%d/%d dsq_id=%s", p->scx.sticky_cpu, p->scx.holding_cpu, dsq_id_buf); dump_line(s, " dsq_vtime=%llu slice=%llu weight=%u", p->scx.dsq_vtime, p->scx.slice, p->scx.weight); dump_line(s, " cpus=%*pb no_mig=%u", cpumask_pr_args(p->cpus_ptr), p->migration_disabled); if (SCX_HAS_OP(sch, dump_task)) { ops_dump_init(s, " "); SCX_CALL_OP(sch, SCX_KF_REST, dump_task, NULL, dctx, p); ops_dump_exit(); } #ifdef CONFIG_STACKTRACE bt_len = stack_trace_save_tsk(p, bt, SCX_EXIT_BT_LEN, 1); #endif if (bt_len) { dump_newline(s); dump_stack_trace(s, " ", bt, bt_len); } } /* * Dump scheduler state. If @dump_all_tasks is true, dump all tasks regardless * of which scheduler they belong to. If false, only dump tasks owned by @sch. * For SysRq-D dumps, @dump_all_tasks=false since all schedulers are dumped * separately. For error dumps, @dump_all_tasks=true since only the failing * scheduler is dumped. */ static void scx_dump_state(struct scx_sched *sch, struct scx_exit_info *ei, size_t dump_len, bool dump_all_tasks) { static const char trunc_marker[] = "\n\n~~~~ TRUNCATED ~~~~\n"; struct scx_dump_ctx dctx = { .kind = ei->kind, .exit_code = ei->exit_code, .reason = ei->reason, .at_ns = ktime_get_ns(), .at_jiffies = jiffies, }; struct seq_buf s; struct scx_event_stats events; char *buf; int cpu; guard(raw_spinlock_irqsave)(&scx_dump_lock); if (sch->dump_disabled) return; seq_buf_init(&s, ei->dump, dump_len); #ifdef CONFIG_EXT_SUB_SCHED if (sch->level == 0) dump_line(&s, "%s: root", sch->ops.name); else dump_line(&s, "%s: sub%d-%llu %s", sch->ops.name, sch->level, sch->ops.sub_cgroup_id, sch->cgrp_path); #endif if (ei->kind == SCX_EXIT_NONE) { dump_line(&s, "Debug dump triggered by %s", ei->reason); } else { dump_line(&s, "%s[%d] triggered exit kind %d:", current->comm, current->pid, ei->kind); dump_line(&s, " %s (%s)", ei->reason, ei->msg); dump_newline(&s); dump_line(&s, "Backtrace:"); dump_stack_trace(&s, " ", ei->bt, ei->bt_len); } if (SCX_HAS_OP(sch, dump)) { ops_dump_init(&s, ""); SCX_CALL_OP(sch, SCX_KF_UNLOCKED, dump, NULL, &dctx); ops_dump_exit(); } dump_newline(&s); dump_line(&s, "CPU states"); dump_line(&s, "----------"); for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); struct rq_flags rf; struct task_struct *p; struct seq_buf ns; size_t avail, used; bool idle; rq_lock_irqsave(rq, &rf); idle = list_empty(&rq->scx.runnable_list) && rq->curr->sched_class == &idle_sched_class; if (idle && !SCX_HAS_OP(sch, dump_cpu)) goto next; /* * We don't yet know whether ops.dump_cpu() will produce output * and we may want to skip the default CPU dump if it doesn't. * Use a nested seq_buf to generate the standard dump so that we * can decide whether to commit later. */ avail = seq_buf_get_buf(&s, &buf); seq_buf_init(&ns, buf, avail); dump_newline(&ns); dump_line(&ns, "CPU %-4d: nr_run=%u flags=0x%x cpu_rel=%d ops_qseq=%lu ksync=%lu", cpu, rq->scx.nr_running, rq->scx.flags, rq->scx.cpu_released, rq->scx.ops_qseq, rq->scx.kick_sync); dump_line(&ns, " curr=%s[%d] class=%ps", rq->curr->comm, rq->curr->pid, rq->curr->sched_class); if (!cpumask_empty(rq->scx.cpus_to_kick)) dump_line(&ns, " cpus_to_kick : %*pb", cpumask_pr_args(rq->scx.cpus_to_kick)); if (!cpumask_empty(rq->scx.cpus_to_kick_if_idle)) dump_line(&ns, " idle_to_kick : %*pb", cpumask_pr_args(rq->scx.cpus_to_kick_if_idle)); if (!cpumask_empty(rq->scx.cpus_to_preempt)) dump_line(&ns, " cpus_to_preempt: %*pb", cpumask_pr_args(rq->scx.cpus_to_preempt)); if (!cpumask_empty(rq->scx.cpus_to_wait)) dump_line(&ns, " cpus_to_wait : %*pb", cpumask_pr_args(rq->scx.cpus_to_wait)); if (!cpumask_empty(rq->scx.cpus_to_sync)) dump_line(&ns, " cpus_to_sync : %*pb", cpumask_pr_args(rq->scx.cpus_to_sync)); used = seq_buf_used(&ns); if (SCX_HAS_OP(sch, dump_cpu)) { ops_dump_init(&ns, " "); SCX_CALL_OP(sch, SCX_KF_REST, dump_cpu, NULL, &dctx, cpu, idle); ops_dump_exit(); } /* * If idle && nothing generated by ops.dump_cpu(), there's * nothing interesting. Skip. */ if (idle && used == seq_buf_used(&ns)) goto next; /* * $s may already have overflowed when $ns was created. If so, * calling commit on it will trigger BUG. */ if (avail) { seq_buf_commit(&s, seq_buf_used(&ns)); if (seq_buf_has_overflowed(&ns)) seq_buf_set_overflow(&s); } if (rq->curr->sched_class == &ext_sched_class && (dump_all_tasks || scx_task_on_sched(sch, rq->curr))) scx_dump_task(sch, &s, &dctx, rq->curr, '*'); list_for_each_entry(p, &rq->scx.runnable_list, scx.runnable_node) if (dump_all_tasks || scx_task_on_sched(sch, p)) scx_dump_task(sch, &s, &dctx, p, ' '); next: rq_unlock_irqrestore(rq, &rf); } dump_newline(&s); dump_line(&s, "Event counters"); dump_line(&s, "--------------"); scx_read_events(sch, &events); scx_dump_event(s, &events, SCX_EV_SELECT_CPU_FALLBACK); scx_dump_event(s, &events, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE); scx_dump_event(s, &events, SCX_EV_DISPATCH_KEEP_LAST); scx_dump_event(s, &events, SCX_EV_ENQ_SKIP_EXITING); scx_dump_event(s, &events, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED); scx_dump_event(s, &events, SCX_EV_REENQ_IMMED); scx_dump_event(s, &events, SCX_EV_REENQ_LOCAL_REPEAT); scx_dump_event(s, &events, SCX_EV_REFILL_SLICE_DFL); scx_dump_event(s, &events, SCX_EV_BYPASS_DURATION); scx_dump_event(s, &events, SCX_EV_BYPASS_DISPATCH); scx_dump_event(s, &events, SCX_EV_BYPASS_ACTIVATE); scx_dump_event(s, &events, SCX_EV_INSERT_NOT_OWNED); scx_dump_event(s, &events, SCX_EV_SUB_BYPASS_DISPATCH); if (seq_buf_has_overflowed(&s) && dump_len >= sizeof(trunc_marker)) memcpy(ei->dump + dump_len - sizeof(trunc_marker), trunc_marker, sizeof(trunc_marker)); } static void scx_disable_irq_workfn(struct irq_work *irq_work) { struct scx_sched *sch = container_of(irq_work, struct scx_sched, disable_irq_work); struct scx_exit_info *ei = sch->exit_info; if (ei->kind >= SCX_EXIT_ERROR) scx_dump_state(sch, ei, sch->ops.exit_dump_len, true); kthread_queue_work(sch->helper, &sch->disable_work); } static bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, const char *fmt, va_list args) { struct scx_exit_info *ei = sch->exit_info; guard(preempt)(); if (!scx_claim_exit(sch, kind)) return false; ei->exit_code = exit_code; #ifdef CONFIG_STACKTRACE if (kind >= SCX_EXIT_ERROR) ei->bt_len = stack_trace_save(ei->bt, SCX_EXIT_BT_LEN, 1); #endif vscnprintf(ei->msg, SCX_EXIT_MSG_LEN, fmt, args); /* * Set ei->kind and ->reason for scx_dump_state(). They'll be set again * in scx_disable_workfn(). */ ei->kind = kind; ei->reason = scx_exit_reason(ei->kind); irq_work_queue(&sch->disable_irq_work); return true; } static int alloc_kick_syncs(void) { int cpu; /* * Allocate per-CPU arrays sized by nr_cpu_ids. Use kvzalloc as size * can exceed percpu allocator limits on large machines. */ for_each_possible_cpu(cpu) { struct scx_kick_syncs **ksyncs = per_cpu_ptr(&scx_kick_syncs, cpu); struct scx_kick_syncs *new_ksyncs; WARN_ON_ONCE(rcu_access_pointer(*ksyncs)); new_ksyncs = kvzalloc_node(struct_size(new_ksyncs, syncs, nr_cpu_ids), GFP_KERNEL, cpu_to_node(cpu)); if (!new_ksyncs) { free_kick_syncs(); return -ENOMEM; } rcu_assign_pointer(*ksyncs, new_ksyncs); } return 0; } static void free_pnode(struct scx_sched_pnode *pnode) { if (!pnode) return; exit_dsq(&pnode->global_dsq); kfree(pnode); } static struct scx_sched_pnode *alloc_pnode(struct scx_sched *sch, int node) { struct scx_sched_pnode *pnode; pnode = kzalloc_node(sizeof(*pnode), GFP_KERNEL, node); if (!pnode) return NULL; if (init_dsq(&pnode->global_dsq, SCX_DSQ_GLOBAL, sch)) { kfree(pnode); return NULL; } return pnode; } /* * Allocate and initialize a new scx_sched. @cgrp's reference is always * consumed whether the function succeeds or fails. */ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops, struct cgroup *cgrp, struct scx_sched *parent) { struct scx_sched *sch; s32 level = parent ? parent->level + 1 : 0; s32 node, cpu, ret, bypass_fail_cpu = nr_cpu_ids; sch = kzalloc_flex(*sch, ancestors, level + 1); if (!sch) { ret = -ENOMEM; goto err_put_cgrp; } sch->exit_info = alloc_exit_info(ops->exit_dump_len); if (!sch->exit_info) { ret = -ENOMEM; goto err_free_sch; } ret = rhashtable_init(&sch->dsq_hash, &dsq_hash_params); if (ret < 0) goto err_free_ei; sch->pnode = kzalloc_objs(sch->pnode[0], nr_node_ids); if (!sch->pnode) { ret = -ENOMEM; goto err_free_hash; } for_each_node_state(node, N_POSSIBLE) { sch->pnode[node] = alloc_pnode(sch, node); if (!sch->pnode[node]) { ret = -ENOMEM; goto err_free_pnode; } } sch->dsp_max_batch = ops->dispatch_max_batch ?: SCX_DSP_DFL_MAX_BATCH; sch->pcpu = __alloc_percpu(struct_size_t(struct scx_sched_pcpu, dsp_ctx.buf, sch->dsp_max_batch), __alignof__(struct scx_sched_pcpu)); if (!sch->pcpu) { ret = -ENOMEM; goto err_free_pnode; } for_each_possible_cpu(cpu) { ret = init_dsq(bypass_dsq(sch, cpu), SCX_DSQ_BYPASS, sch); if (ret) { bypass_fail_cpu = cpu; goto err_free_pcpu; } } for_each_possible_cpu(cpu) { struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); pcpu->sch = sch; INIT_LIST_HEAD(&pcpu->deferred_reenq_local.node); } sch->helper = kthread_run_worker(0, "sched_ext_helper"); if (IS_ERR(sch->helper)) { ret = PTR_ERR(sch->helper); goto err_free_pcpu; } sched_set_fifo(sch->helper->task); if (parent) memcpy(sch->ancestors, parent->ancestors, level * sizeof(parent->ancestors[0])); sch->ancestors[level] = sch; sch->level = level; if (ops->timeout_ms) sch->watchdog_timeout = msecs_to_jiffies(ops->timeout_ms); else sch->watchdog_timeout = SCX_WATCHDOG_MAX_TIMEOUT; sch->slice_dfl = SCX_SLICE_DFL; atomic_set(&sch->exit_kind, SCX_EXIT_NONE); init_irq_work(&sch->disable_irq_work, scx_disable_irq_workfn); kthread_init_work(&sch->disable_work, scx_disable_workfn); timer_setup(&sch->bypass_lb_timer, scx_bypass_lb_timerfn, 0); sch->ops = *ops; rcu_assign_pointer(ops->priv, sch); sch->kobj.kset = scx_kset; #ifdef CONFIG_EXT_SUB_SCHED char *buf = kzalloc(PATH_MAX, GFP_KERNEL); if (!buf) { ret = -ENOMEM; goto err_stop_helper; } cgroup_path(cgrp, buf, PATH_MAX); sch->cgrp_path = kstrdup(buf, GFP_KERNEL); kfree(buf); if (!sch->cgrp_path) { ret = -ENOMEM; goto err_stop_helper; } sch->cgrp = cgrp; INIT_LIST_HEAD(&sch->children); INIT_LIST_HEAD(&sch->sibling); if (parent) ret = kobject_init_and_add(&sch->kobj, &scx_ktype, &parent->sub_kset->kobj, "sub-%llu", cgroup_id(cgrp)); else ret = kobject_init_and_add(&sch->kobj, &scx_ktype, NULL, "root"); if (ret < 0) { kobject_put(&sch->kobj); return ERR_PTR(ret); } if (ops->sub_attach) { sch->sub_kset = kset_create_and_add("sub", NULL, &sch->kobj); if (!sch->sub_kset) { kobject_put(&sch->kobj); return ERR_PTR(-ENOMEM); } } #else /* CONFIG_EXT_SUB_SCHED */ ret = kobject_init_and_add(&sch->kobj, &scx_ktype, NULL, "root"); if (ret < 0) { kobject_put(&sch->kobj); return ERR_PTR(ret); } #endif /* CONFIG_EXT_SUB_SCHED */ return sch; #ifdef CONFIG_EXT_SUB_SCHED err_stop_helper: kthread_destroy_worker(sch->helper); #endif err_free_pcpu: for_each_possible_cpu(cpu) { if (cpu == bypass_fail_cpu) break; exit_dsq(bypass_dsq(sch, cpu)); } free_percpu(sch->pcpu); err_free_pnode: for_each_node_state(node, N_POSSIBLE) free_pnode(sch->pnode[node]); kfree(sch->pnode); err_free_hash: rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); err_free_ei: free_exit_info(sch->exit_info); err_free_sch: kfree(sch); err_put_cgrp: #if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED) cgroup_put(cgrp); #endif return ERR_PTR(ret); } static int check_hotplug_seq(struct scx_sched *sch, const struct sched_ext_ops *ops) { unsigned long long global_hotplug_seq; /* * If a hotplug event has occurred between when a scheduler was * initialized, and when we were able to attach, exit and notify user * space about it. */ if (ops->hotplug_seq) { global_hotplug_seq = atomic_long_read(&scx_hotplug_seq); if (ops->hotplug_seq != global_hotplug_seq) { scx_exit(sch, SCX_EXIT_UNREG_KERN, SCX_ECODE_ACT_RESTART | SCX_ECODE_RSN_HOTPLUG, "expected hotplug seq %llu did not match actual %llu", ops->hotplug_seq, global_hotplug_seq); return -EBUSY; } } return 0; } static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops) { /* * It doesn't make sense to specify the SCX_OPS_ENQ_LAST flag if the * ops.enqueue() callback isn't implemented. */ if ((ops->flags & SCX_OPS_ENQ_LAST) && !ops->enqueue) { scx_error(sch, "SCX_OPS_ENQ_LAST requires ops.enqueue() to be implemented"); return -EINVAL; } /* * SCX_OPS_BUILTIN_IDLE_PER_NODE requires built-in CPU idle * selection policy to be enabled. */ if ((ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE) && (ops->update_idle && !(ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE))) { scx_error(sch, "SCX_OPS_BUILTIN_IDLE_PER_NODE requires CPU idle selection enabled"); return -EINVAL; } if (ops->cpu_acquire || ops->cpu_release) pr_warn("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n"); return 0; } /* * scx_enable() is offloaded to a dedicated system-wide RT kthread to avoid * starvation. During the READY -> ENABLED task switching loop, the calling * thread's sched_class gets switched from fair to ext. As fair has higher * priority than ext, the calling thread can be indefinitely starved under * fair-class saturation, leading to a system hang. */ struct scx_enable_cmd { struct kthread_work work; struct sched_ext_ops *ops; int ret; }; static void scx_root_enable_workfn(struct kthread_work *work) { struct scx_enable_cmd *cmd = container_of(work, struct scx_enable_cmd, work); struct sched_ext_ops *ops = cmd->ops; struct cgroup *cgrp = root_cgroup(); struct scx_sched *sch; struct scx_task_iter sti; struct task_struct *p; int i, cpu, ret; mutex_lock(&scx_enable_mutex); if (scx_enable_state() != SCX_DISABLED) { ret = -EBUSY; goto err_unlock; } ret = alloc_kick_syncs(); if (ret) goto err_unlock; #if defined(CONFIG_EXT_GROUP_SCHED) || defined(CONFIG_EXT_SUB_SCHED) cgroup_get(cgrp); #endif sch = scx_alloc_and_add_sched(ops, cgrp, NULL); if (IS_ERR(sch)) { ret = PTR_ERR(sch); goto err_free_ksyncs; } /* * Transition to ENABLING and clear exit info to arm the disable path. * Failure triggers full disabling from here on. */ WARN_ON_ONCE(scx_set_enable_state(SCX_ENABLING) != SCX_DISABLED); WARN_ON_ONCE(scx_root); atomic_long_set(&scx_nr_rejected, 0); for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); rq->scx.local_dsq.sched = sch; rq->scx.cpuperf_target = SCX_CPUPERF_ONE; } /* * Keep CPUs stable during enable so that the BPF scheduler can track * online CPUs by watching ->on/offline_cpu() after ->init(). */ cpus_read_lock(); /* * Make the scheduler instance visible. Must be inside cpus_read_lock(). * See handle_hotplug(). */ rcu_assign_pointer(scx_root, sch); ret = scx_link_sched(sch); if (ret) goto err_disable; scx_idle_enable(ops); if (sch->ops.init) { ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, init, NULL); if (ret) { ret = ops_sanitize_err(sch, "init", ret); cpus_read_unlock(); scx_error(sch, "ops.init() failed (%d)", ret); goto err_disable; } sch->exit_info->flags |= SCX_EFLAG_INITIALIZED; } for (i = SCX_OPI_CPU_HOTPLUG_BEGIN; i < SCX_OPI_CPU_HOTPLUG_END; i++) if (((void (**)(void))ops)[i]) set_bit(i, sch->has_op); ret = check_hotplug_seq(sch, ops); if (ret) { cpus_read_unlock(); goto err_disable; } scx_idle_update_selcpu_topology(ops); cpus_read_unlock(); ret = validate_ops(sch, ops); if (ret) goto err_disable; /* * Once __scx_enabled is set, %current can be switched to SCX anytime. * This can lead to stalls as some BPF schedulers (e.g. userspace * scheduling) may not function correctly before all tasks are switched. * Init in bypass mode to guarantee forward progress. */ scx_bypass(sch, true); for (i = SCX_OPI_NORMAL_BEGIN; i < SCX_OPI_NORMAL_END; i++) if (((void (**)(void))ops)[i]) set_bit(i, sch->has_op); if (sch->ops.cpu_acquire || sch->ops.cpu_release) sch->ops.flags |= SCX_OPS_HAS_CPU_PREEMPT; /* * Lock out forks, cgroup on/offlining and moves before opening the * floodgate so that they don't wander into the operations prematurely. */ percpu_down_write(&scx_fork_rwsem); WARN_ON_ONCE(scx_init_task_enabled); scx_init_task_enabled = true; /* * Enable ops for every task. Fork is excluded by scx_fork_rwsem * preventing new tasks from being added. No need to exclude tasks * leaving as sched_ext_free() can handle both prepped and enabled * tasks. Prep all tasks first and then enable them with preemption * disabled. * * All cgroups should be initialized before scx_init_task() so that the * BPF scheduler can reliably track each task's cgroup membership from * scx_init_task(). Lock out cgroup on/offlining and task migrations * while tasks are being initialized so that scx_cgroup_can_attach() * never sees uninitialized tasks. */ scx_cgroup_lock(); set_cgroup_sched(sch_cgroup(sch), sch); ret = scx_cgroup_init(sch); if (ret) goto err_disable_unlock_all; scx_task_iter_start(&sti, NULL); while ((p = scx_task_iter_next_locked(&sti))) { /* * @p may already be dead, have lost all its usages counts and * be waiting for RCU grace period before being freed. @p can't * be initialized for SCX in such cases and should be ignored. */ if (!tryget_task_struct(p)) continue; scx_task_iter_unlock(&sti); ret = scx_init_task(sch, p, false); if (ret) { put_task_struct(p); scx_task_iter_stop(&sti); scx_error(sch, "ops.init_task() failed (%d) for %s[%d]", ret, p->comm, p->pid); goto err_disable_unlock_all; } scx_set_task_sched(p, sch); scx_set_task_state(p, SCX_TASK_READY); put_task_struct(p); } scx_task_iter_stop(&sti); scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); /* * All tasks are READY. It's safe to turn on scx_enabled() and switch * all eligible tasks. */ WRITE_ONCE(scx_switching_all, !(ops->flags & SCX_OPS_SWITCH_PARTIAL)); static_branch_enable(&__scx_enabled); /* * We're fully committed and can't fail. The task READY -> ENABLED * transitions here are synchronized against sched_ext_free() through * scx_tasks_lock. */ percpu_down_write(&scx_fork_rwsem); scx_task_iter_start(&sti, NULL); while ((p = scx_task_iter_next_locked(&sti))) { unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE; const struct sched_class *old_class = p->sched_class; const struct sched_class *new_class = scx_setscheduler_class(p); if (scx_get_task_state(p) != SCX_TASK_READY) continue; if (old_class != new_class) queue_flags |= DEQUEUE_CLASS; scoped_guard (sched_change, p, queue_flags) { p->scx.slice = READ_ONCE(sch->slice_dfl); p->sched_class = new_class; } } scx_task_iter_stop(&sti); percpu_up_write(&scx_fork_rwsem); scx_bypass(sch, false); if (!scx_tryset_enable_state(SCX_ENABLED, SCX_ENABLING)) { WARN_ON_ONCE(atomic_read(&sch->exit_kind) == SCX_EXIT_NONE); goto err_disable; } if (!(ops->flags & SCX_OPS_SWITCH_PARTIAL)) static_branch_enable(&__scx_switched_all); pr_info("sched_ext: BPF scheduler \"%s\" enabled%s\n", sch->ops.name, scx_switched_all() ? "" : " (partial)"); kobject_uevent(&sch->kobj, KOBJ_ADD); mutex_unlock(&scx_enable_mutex); atomic_long_inc(&scx_enable_seq); cmd->ret = 0; return; err_free_ksyncs: free_kick_syncs(); err_unlock: mutex_unlock(&scx_enable_mutex); cmd->ret = ret; return; err_disable_unlock_all: scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); /* we'll soon enter disable path, keep bypass on */ err_disable: mutex_unlock(&scx_enable_mutex); /* * Returning an error code here would not pass all the error information * to userspace. Record errno using scx_error() for cases scx_error() * wasn't already invoked and exit indicating success so that the error * is notified through ops.exit() with all the details. * * Flush scx_disable_work to ensure that error is reported before init * completion. sch's base reference will be put by bpf_scx_unreg(). */ scx_error(sch, "scx_root_enable() failed (%d)", ret); kthread_flush_work(&sch->disable_work); cmd->ret = 0; } #ifdef CONFIG_EXT_SUB_SCHED /* verify that a scheduler can be attached to @cgrp and return the parent */ static struct scx_sched *find_parent_sched(struct cgroup *cgrp) { struct scx_sched *parent = cgrp->scx_sched; struct scx_sched *pos; lockdep_assert_held(&scx_sched_lock); /* can't attach twice to the same cgroup */ if (parent->cgrp == cgrp) return ERR_PTR(-EBUSY); /* does $parent allow sub-scheds? */ if (!parent->ops.sub_attach) return ERR_PTR(-EOPNOTSUPP); /* can't insert between $parent and its exiting children */ list_for_each_entry(pos, &parent->children, sibling) if (cgroup_is_descendant(pos->cgrp, cgrp)) return ERR_PTR(-EBUSY); return parent; } static bool assert_task_ready_or_enabled(struct task_struct *p) { u32 state = scx_get_task_state(p); switch (state) { case SCX_TASK_READY: case SCX_TASK_ENABLED: return true; default: WARN_ONCE(true, "sched_ext: Invalid task state %d for %s[%d] during enabling sub sched", state, p->comm, p->pid); return false; } } static void scx_sub_enable_workfn(struct kthread_work *work) { struct scx_enable_cmd *cmd = container_of(work, struct scx_enable_cmd, work); struct sched_ext_ops *ops = cmd->ops; struct cgroup *cgrp; struct scx_sched *parent, *sch; struct scx_task_iter sti; struct task_struct *p; s32 i, ret; mutex_lock(&scx_enable_mutex); if (!scx_enabled()) { ret = -ENODEV; goto out_unlock; } cgrp = cgroup_get_from_id(ops->sub_cgroup_id); if (IS_ERR(cgrp)) { ret = PTR_ERR(cgrp); goto out_unlock; } raw_spin_lock_irq(&scx_sched_lock); parent = find_parent_sched(cgrp); if (IS_ERR(parent)) { raw_spin_unlock_irq(&scx_sched_lock); ret = PTR_ERR(parent); goto out_put_cgrp; } kobject_get(&parent->kobj); raw_spin_unlock_irq(&scx_sched_lock); /* scx_alloc_and_add_sched() consumes @cgrp whether it succeeds or not */ sch = scx_alloc_and_add_sched(ops, cgrp, parent); kobject_put(&parent->kobj); if (IS_ERR(sch)) { ret = PTR_ERR(sch); goto out_unlock; } ret = scx_link_sched(sch); if (ret) goto err_disable; if (sch->level >= SCX_SUB_MAX_DEPTH) { scx_error(sch, "max nesting depth %d violated", SCX_SUB_MAX_DEPTH); goto err_disable; } if (sch->ops.init) { ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, init, NULL); if (ret) { ret = ops_sanitize_err(sch, "init", ret); scx_error(sch, "ops.init() failed (%d)", ret); goto err_disable; } sch->exit_info->flags |= SCX_EFLAG_INITIALIZED; } if (validate_ops(sch, ops)) goto err_disable; struct scx_sub_attach_args sub_attach_args = { .ops = &sch->ops, .cgroup_path = sch->cgrp_path, }; ret = SCX_CALL_OP_RET(parent, SCX_KF_UNLOCKED, sub_attach, NULL, &sub_attach_args); if (ret) { ret = ops_sanitize_err(sch, "sub_attach", ret); scx_error(sch, "parent rejected (%d)", ret); goto err_disable; } sch->sub_attached = true; scx_bypass(sch, true); for (i = SCX_OPI_BEGIN; i < SCX_OPI_END; i++) if (((void (**)(void))ops)[i]) set_bit(i, sch->has_op); percpu_down_write(&scx_fork_rwsem); scx_cgroup_lock(); /* * Set cgroup->scx_sched's and check CSS_ONLINE. Either we see * !CSS_ONLINE or scx_cgroup_lifetime_notify() sees and shoots us down. */ set_cgroup_sched(sch_cgroup(sch), sch); if (!(cgrp->self.flags & CSS_ONLINE)) { scx_error(sch, "cgroup is not online"); goto err_unlock_and_disable; } /* * Initialize tasks for the new child $sch without exiting them for * $parent so that the tasks can always be reverted back to $parent * sched on child init failure. */ WARN_ON_ONCE(scx_enabling_sub_sched); scx_enabling_sub_sched = sch; scx_task_iter_start(&sti, sch->cgrp); while ((p = scx_task_iter_next_locked(&sti))) { struct rq *rq; struct rq_flags rf; /* * Task iteration may visit the same task twice when racing * against exiting. Use %SCX_TASK_SUB_INIT to mark tasks which * finished __scx_init_task() and skip if set. * * A task may exit and get freed between __scx_init_task() * completion and scx_enable_task(). In such cases, * scx_disable_and_exit_task() must exit the task for both the * parent and child scheds. */ if (p->scx.flags & SCX_TASK_SUB_INIT) continue; /* see scx_root_enable() */ if (!tryget_task_struct(p)) continue; if (!assert_task_ready_or_enabled(p)) { ret = -EINVAL; goto abort; } scx_task_iter_unlock(&sti); /* * As $p is still on $parent, it can't be transitioned to INIT. * Let's worry about task state later. Use __scx_init_task(). */ ret = __scx_init_task(sch, p, false); if (ret) goto abort; rq = task_rq_lock(p, &rf); p->scx.flags |= SCX_TASK_SUB_INIT; task_rq_unlock(rq, p, &rf); put_task_struct(p); } scx_task_iter_stop(&sti); /* * All tasks are prepped. Disable/exit tasks for $parent and enable for * the new @sch. */ scx_task_iter_start(&sti, sch->cgrp); while ((p = scx_task_iter_next_locked(&sti))) { /* * Use clearing of %SCX_TASK_SUB_INIT to detect and skip * duplicate iterations. */ if (!(p->scx.flags & SCX_TASK_SUB_INIT)) continue; scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) { /* * $p must be either READY or ENABLED. If ENABLED, * __scx_disabled_and_exit_task() first disables and * makes it READY. However, after exiting $p, it will * leave $p as READY. */ assert_task_ready_or_enabled(p); __scx_disable_and_exit_task(parent, p); /* * $p is now only initialized for @sch and READY, which * is what we want. Assign it to @sch and enable. */ rcu_assign_pointer(p->scx.sched, sch); scx_enable_task(sch, p); p->scx.flags &= ~SCX_TASK_SUB_INIT; } } scx_task_iter_stop(&sti); scx_enabling_sub_sched = NULL; scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); scx_bypass(sch, false); pr_info("sched_ext: BPF sub-scheduler \"%s\" enabled\n", sch->ops.name); kobject_uevent(&sch->kobj, KOBJ_ADD); ret = 0; goto out_unlock; out_put_cgrp: cgroup_put(cgrp); out_unlock: mutex_unlock(&scx_enable_mutex); cmd->ret = ret; return; abort: put_task_struct(p); scx_task_iter_stop(&sti); scx_enabling_sub_sched = NULL; scx_task_iter_start(&sti, sch->cgrp); while ((p = scx_task_iter_next_locked(&sti))) { if (p->scx.flags & SCX_TASK_SUB_INIT) { __scx_disable_and_exit_task(sch, p); p->scx.flags &= ~SCX_TASK_SUB_INIT; } } scx_task_iter_stop(&sti); err_unlock_and_disable: /* we'll soon enter disable path, keep bypass on */ scx_cgroup_unlock(); percpu_up_write(&scx_fork_rwsem); err_disable: mutex_unlock(&scx_enable_mutex); kthread_flush_work(&sch->disable_work); cmd->ret = 0; } static s32 scx_cgroup_lifetime_notify(struct notifier_block *nb, unsigned long action, void *data) { struct cgroup *cgrp = data; struct cgroup *parent = cgroup_parent(cgrp); if (!cgroup_on_dfl(cgrp)) return NOTIFY_OK; switch (action) { case CGROUP_LIFETIME_ONLINE: /* inherit ->scx_sched from $parent */ if (parent) rcu_assign_pointer(cgrp->scx_sched, parent->scx_sched); break; case CGROUP_LIFETIME_OFFLINE: /* if there is a sched attached, shoot it down */ if (cgrp->scx_sched && cgrp->scx_sched->cgrp == cgrp) scx_exit(cgrp->scx_sched, SCX_EXIT_UNREG_KERN, SCX_ECODE_RSN_CGROUP_OFFLINE, "cgroup %llu going offline", cgroup_id(cgrp)); break; } return NOTIFY_OK; } static struct notifier_block scx_cgroup_lifetime_nb = { .notifier_call = scx_cgroup_lifetime_notify, }; static s32 __init scx_cgroup_lifetime_notifier_init(void) { return blocking_notifier_chain_register(&cgroup_lifetime_notifier, &scx_cgroup_lifetime_nb); } core_initcall(scx_cgroup_lifetime_notifier_init); #endif /* CONFIG_EXT_SUB_SCHED */ static s32 scx_enable(struct sched_ext_ops *ops, struct bpf_link *link) { static struct kthread_worker *helper; static DEFINE_MUTEX(helper_mutex); struct scx_enable_cmd cmd; if (!cpumask_equal(housekeeping_cpumask(HK_TYPE_DOMAIN), cpu_possible_mask)) { pr_err("sched_ext: Not compatible with \"isolcpus=\" domain isolation\n"); return -EINVAL; } if (!READ_ONCE(helper)) { mutex_lock(&helper_mutex); if (!helper) { struct kthread_worker *w = kthread_run_worker(0, "scx_enable_helper"); if (IS_ERR_OR_NULL(w)) { mutex_unlock(&helper_mutex); return -ENOMEM; } sched_set_fifo(w->task); WRITE_ONCE(helper, w); } mutex_unlock(&helper_mutex); } #ifdef CONFIG_EXT_SUB_SCHED if (ops->sub_cgroup_id > 1) kthread_init_work(&cmd.work, scx_sub_enable_workfn); else #endif /* CONFIG_EXT_SUB_SCHED */ kthread_init_work(&cmd.work, scx_root_enable_workfn); cmd.ops = ops; kthread_queue_work(READ_ONCE(helper), &cmd.work); kthread_flush_work(&cmd.work); return cmd.ret; } /******************************************************************************** * bpf_struct_ops plumbing. */ #include #include #include static const struct btf_type *task_struct_type; static bool bpf_scx_is_valid_access(int off, int size, enum bpf_access_type type, const struct bpf_prog *prog, struct bpf_insn_access_aux *info) { if (type != BPF_READ) return false; if (off < 0 || off >= sizeof(__u64) * MAX_BPF_FUNC_ARGS) return false; if (off % size != 0) return false; return btf_ctx_access(off, size, type, prog, info); } static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log, const struct bpf_reg_state *reg, int off, int size) { const struct btf_type *t; t = btf_type_by_id(reg->btf, reg->btf_id); if (t == task_struct_type) { /* * COMPAT: Will be removed in v6.23. */ if ((off >= offsetof(struct task_struct, scx.slice) && off + size <= offsetofend(struct task_struct, scx.slice)) || (off >= offsetof(struct task_struct, scx.dsq_vtime) && off + size <= offsetofend(struct task_struct, scx.dsq_vtime))) { pr_warn("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()"); return SCALAR_VALUE; } if (off >= offsetof(struct task_struct, scx.disallow) && off + size <= offsetofend(struct task_struct, scx.disallow)) return SCALAR_VALUE; } return -EACCES; } static const struct bpf_verifier_ops bpf_scx_verifier_ops = { .get_func_proto = bpf_base_func_proto, .is_valid_access = bpf_scx_is_valid_access, .btf_struct_access = bpf_scx_btf_struct_access, }; static int bpf_scx_init_member(const struct btf_type *t, const struct btf_member *member, void *kdata, const void *udata) { const struct sched_ext_ops *uops = udata; struct sched_ext_ops *ops = kdata; u32 moff = __btf_member_bit_offset(t, member) / 8; int ret; switch (moff) { case offsetof(struct sched_ext_ops, dispatch_max_batch): if (*(u32 *)(udata + moff) > INT_MAX) return -E2BIG; ops->dispatch_max_batch = *(u32 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, flags): if (*(u64 *)(udata + moff) & ~SCX_OPS_ALL_FLAGS) return -EINVAL; ops->flags = *(u64 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, name): ret = bpf_obj_name_cpy(ops->name, uops->name, sizeof(ops->name)); if (ret < 0) return ret; if (ret == 0) return -EINVAL; return 1; case offsetof(struct sched_ext_ops, timeout_ms): if (msecs_to_jiffies(*(u32 *)(udata + moff)) > SCX_WATCHDOG_MAX_TIMEOUT) return -E2BIG; ops->timeout_ms = *(u32 *)(udata + moff); return 1; case offsetof(struct sched_ext_ops, exit_dump_len): ops->exit_dump_len = *(u32 *)(udata + moff) ?: SCX_EXIT_DUMP_DFL_LEN; return 1; case offsetof(struct sched_ext_ops, hotplug_seq): ops->hotplug_seq = *(u64 *)(udata + moff); return 1; #ifdef CONFIG_EXT_SUB_SCHED case offsetof(struct sched_ext_ops, sub_cgroup_id): ops->sub_cgroup_id = *(u64 *)(udata + moff); return 1; #endif /* CONFIG_EXT_SUB_SCHED */ } return 0; } #ifdef CONFIG_EXT_SUB_SCHED static void scx_pstack_recursion_on_dispatch(struct bpf_prog *prog) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(prog->aux); if (unlikely(!sch)) return; scx_error(sch, "dispatch recursion detected"); } #endif /* CONFIG_EXT_SUB_SCHED */ static int bpf_scx_check_member(const struct btf_type *t, const struct btf_member *member, const struct bpf_prog *prog) { u32 moff = __btf_member_bit_offset(t, member) / 8; switch (moff) { case offsetof(struct sched_ext_ops, init_task): #ifdef CONFIG_EXT_GROUP_SCHED case offsetof(struct sched_ext_ops, cgroup_init): case offsetof(struct sched_ext_ops, cgroup_exit): case offsetof(struct sched_ext_ops, cgroup_prep_move): #endif case offsetof(struct sched_ext_ops, cpu_online): case offsetof(struct sched_ext_ops, cpu_offline): case offsetof(struct sched_ext_ops, init): case offsetof(struct sched_ext_ops, exit): case offsetof(struct sched_ext_ops, sub_attach): case offsetof(struct sched_ext_ops, sub_detach): break; default: if (prog->sleepable) return -EINVAL; } #ifdef CONFIG_EXT_SUB_SCHED /* * Enable private stack for operations that can nest along the * hierarchy. * * XXX - Ideally, we should only do this for scheds that allow * sub-scheds and sub-scheds themselves but I don't know how to access * struct_ops from here. */ switch (moff) { case offsetof(struct sched_ext_ops, dispatch): prog->aux->priv_stack_requested = true; prog->aux->recursion_detected = scx_pstack_recursion_on_dispatch; } #endif /* CONFIG_EXT_SUB_SCHED */ return 0; } static int bpf_scx_reg(void *kdata, struct bpf_link *link) { return scx_enable(kdata, link); } static void bpf_scx_unreg(void *kdata, struct bpf_link *link) { struct sched_ext_ops *ops = kdata; struct scx_sched *sch = rcu_dereference_protected(ops->priv, true); scx_disable(sch, SCX_EXIT_UNREG); kthread_flush_work(&sch->disable_work); RCU_INIT_POINTER(ops->priv, NULL); kobject_put(&sch->kobj); } static int bpf_scx_init(struct btf *btf) { task_struct_type = btf_type_by_id(btf, btf_tracing_ids[BTF_TRACING_TYPE_TASK]); return 0; } static int bpf_scx_update(void *kdata, void *old_kdata, struct bpf_link *link) { /* * sched_ext does not support updating the actively-loaded BPF * scheduler, as registering a BPF scheduler can always fail if the * scheduler returns an error code for e.g. ops.init(), ops.init_task(), * etc. Similarly, we can always race with unregistration happening * elsewhere, such as with sysrq. */ return -EOPNOTSUPP; } static int bpf_scx_validate(void *kdata) { return 0; } static s32 sched_ext_ops__select_cpu(struct task_struct *p, s32 prev_cpu, u64 wake_flags) { return -EINVAL; } static void sched_ext_ops__enqueue(struct task_struct *p, u64 enq_flags) {} static void sched_ext_ops__dequeue(struct task_struct *p, u64 enq_flags) {} static void sched_ext_ops__dispatch(s32 prev_cpu, struct task_struct *prev__nullable) {} static void sched_ext_ops__tick(struct task_struct *p) {} static void sched_ext_ops__runnable(struct task_struct *p, u64 enq_flags) {} static void sched_ext_ops__running(struct task_struct *p) {} static void sched_ext_ops__stopping(struct task_struct *p, bool runnable) {} static void sched_ext_ops__quiescent(struct task_struct *p, u64 deq_flags) {} static bool sched_ext_ops__yield(struct task_struct *from, struct task_struct *to__nullable) { return false; } static bool sched_ext_ops__core_sched_before(struct task_struct *a, struct task_struct *b) { return false; } static void sched_ext_ops__set_weight(struct task_struct *p, u32 weight) {} static void sched_ext_ops__set_cpumask(struct task_struct *p, const struct cpumask *mask) {} static void sched_ext_ops__update_idle(s32 cpu, bool idle) {} static void sched_ext_ops__cpu_acquire(s32 cpu, struct scx_cpu_acquire_args *args) {} static void sched_ext_ops__cpu_release(s32 cpu, struct scx_cpu_release_args *args) {} static s32 sched_ext_ops__init_task(struct task_struct *p, struct scx_init_task_args *args) { return -EINVAL; } static void sched_ext_ops__exit_task(struct task_struct *p, struct scx_exit_task_args *args) {} static void sched_ext_ops__enable(struct task_struct *p) {} static void sched_ext_ops__disable(struct task_struct *p) {} #ifdef CONFIG_EXT_GROUP_SCHED static s32 sched_ext_ops__cgroup_init(struct cgroup *cgrp, struct scx_cgroup_init_args *args) { return -EINVAL; } static void sched_ext_ops__cgroup_exit(struct cgroup *cgrp) {} static s32 sched_ext_ops__cgroup_prep_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) { return -EINVAL; } static void sched_ext_ops__cgroup_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) {} static void sched_ext_ops__cgroup_cancel_move(struct task_struct *p, struct cgroup *from, struct cgroup *to) {} static void sched_ext_ops__cgroup_set_weight(struct cgroup *cgrp, u32 weight) {} static void sched_ext_ops__cgroup_set_bandwidth(struct cgroup *cgrp, u64 period_us, u64 quota_us, u64 burst_us) {} static void sched_ext_ops__cgroup_set_idle(struct cgroup *cgrp, bool idle) {} #endif /* CONFIG_EXT_GROUP_SCHED */ static s32 sched_ext_ops__sub_attach(struct scx_sub_attach_args *args) { return -EINVAL; } static void sched_ext_ops__sub_detach(struct scx_sub_detach_args *args) {} static void sched_ext_ops__cpu_online(s32 cpu) {} static void sched_ext_ops__cpu_offline(s32 cpu) {} static s32 sched_ext_ops__init(void) { return -EINVAL; } static void sched_ext_ops__exit(struct scx_exit_info *info) {} static void sched_ext_ops__dump(struct scx_dump_ctx *ctx) {} static void sched_ext_ops__dump_cpu(struct scx_dump_ctx *ctx, s32 cpu, bool idle) {} static void sched_ext_ops__dump_task(struct scx_dump_ctx *ctx, struct task_struct *p) {} static struct sched_ext_ops __bpf_ops_sched_ext_ops = { .select_cpu = sched_ext_ops__select_cpu, .enqueue = sched_ext_ops__enqueue, .dequeue = sched_ext_ops__dequeue, .dispatch = sched_ext_ops__dispatch, .tick = sched_ext_ops__tick, .runnable = sched_ext_ops__runnable, .running = sched_ext_ops__running, .stopping = sched_ext_ops__stopping, .quiescent = sched_ext_ops__quiescent, .yield = sched_ext_ops__yield, .core_sched_before = sched_ext_ops__core_sched_before, .set_weight = sched_ext_ops__set_weight, .set_cpumask = sched_ext_ops__set_cpumask, .update_idle = sched_ext_ops__update_idle, .cpu_acquire = sched_ext_ops__cpu_acquire, .cpu_release = sched_ext_ops__cpu_release, .init_task = sched_ext_ops__init_task, .exit_task = sched_ext_ops__exit_task, .enable = sched_ext_ops__enable, .disable = sched_ext_ops__disable, #ifdef CONFIG_EXT_GROUP_SCHED .cgroup_init = sched_ext_ops__cgroup_init, .cgroup_exit = sched_ext_ops__cgroup_exit, .cgroup_prep_move = sched_ext_ops__cgroup_prep_move, .cgroup_move = sched_ext_ops__cgroup_move, .cgroup_cancel_move = sched_ext_ops__cgroup_cancel_move, .cgroup_set_weight = sched_ext_ops__cgroup_set_weight, .cgroup_set_bandwidth = sched_ext_ops__cgroup_set_bandwidth, .cgroup_set_idle = sched_ext_ops__cgroup_set_idle, #endif .sub_attach = sched_ext_ops__sub_attach, .sub_detach = sched_ext_ops__sub_detach, .cpu_online = sched_ext_ops__cpu_online, .cpu_offline = sched_ext_ops__cpu_offline, .init = sched_ext_ops__init, .exit = sched_ext_ops__exit, .dump = sched_ext_ops__dump, .dump_cpu = sched_ext_ops__dump_cpu, .dump_task = sched_ext_ops__dump_task, }; static struct bpf_struct_ops bpf_sched_ext_ops = { .verifier_ops = &bpf_scx_verifier_ops, .reg = bpf_scx_reg, .unreg = bpf_scx_unreg, .check_member = bpf_scx_check_member, .init_member = bpf_scx_init_member, .init = bpf_scx_init, .update = bpf_scx_update, .validate = bpf_scx_validate, .name = "sched_ext_ops", .owner = THIS_MODULE, .cfi_stubs = &__bpf_ops_sched_ext_ops }; /******************************************************************************** * System integration and init. */ static void sysrq_handle_sched_ext_reset(u8 key) { struct scx_sched *sch; rcu_read_lock(); sch = rcu_dereference(scx_root); if (likely(sch)) scx_disable(sch, SCX_EXIT_SYSRQ); else pr_info("sched_ext: BPF schedulers not loaded\n"); rcu_read_unlock(); } static const struct sysrq_key_op sysrq_sched_ext_reset_op = { .handler = sysrq_handle_sched_ext_reset, .help_msg = "reset-sched-ext(S)", .action_msg = "Disable sched_ext and revert all tasks to CFS", .enable_mask = SYSRQ_ENABLE_RTNICE, }; static void sysrq_handle_sched_ext_dump(u8 key) { struct scx_exit_info ei = { .kind = SCX_EXIT_NONE, .reason = "SysRq-D" }; struct scx_sched *sch; list_for_each_entry_rcu(sch, &scx_sched_all, all) scx_dump_state(sch, &ei, 0, false); } static const struct sysrq_key_op sysrq_sched_ext_dump_op = { .handler = sysrq_handle_sched_ext_dump, .help_msg = "dump-sched-ext(D)", .action_msg = "Trigger sched_ext debug dump", .enable_mask = SYSRQ_ENABLE_RTNICE, }; static bool can_skip_idle_kick(struct rq *rq) { lockdep_assert_rq_held(rq); /* * We can skip idle kicking if @rq is going to go through at least one * full SCX scheduling cycle before going idle. Just checking whether * curr is not idle is insufficient because we could be racing * balance_one() trying to pull the next task from a remote rq, which * may fail, and @rq may become idle afterwards. * * The race window is small and we don't and can't guarantee that @rq is * only kicked while idle anyway. Skip only when sure. */ return !is_idle_task(rq->curr) && !(rq->scx.flags & SCX_RQ_IN_BALANCE); } static bool kick_one_cpu(s32 cpu, struct rq *this_rq, unsigned long *ksyncs) { struct rq *rq = cpu_rq(cpu); struct scx_rq *this_scx = &this_rq->scx; const struct sched_class *cur_class; bool should_wait = false; unsigned long flags; raw_spin_rq_lock_irqsave(rq, flags); cur_class = rq->curr->sched_class; /* * During CPU hotplug, a CPU may depend on kicking itself to make * forward progress. Allow kicking self regardless of online state. If * @cpu is running a higher class task, we have no control over @cpu. * Skip kicking. */ if ((cpu_online(cpu) || cpu == cpu_of(this_rq)) && !sched_class_above(cur_class, &ext_sched_class)) { if (cpumask_test_cpu(cpu, this_scx->cpus_to_preempt)) { if (cur_class == &ext_sched_class) rq->curr->scx.slice = 0; cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt); } if (cpumask_test_cpu(cpu, this_scx->cpus_to_wait)) { if (cur_class == &ext_sched_class) { cpumask_set_cpu(cpu, this_scx->cpus_to_sync); ksyncs[cpu] = rq->scx.kick_sync; should_wait = true; } cpumask_clear_cpu(cpu, this_scx->cpus_to_wait); } resched_curr(rq); } else { cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt); cpumask_clear_cpu(cpu, this_scx->cpus_to_wait); } raw_spin_rq_unlock_irqrestore(rq, flags); return should_wait; } static void kick_one_cpu_if_idle(s32 cpu, struct rq *this_rq) { struct rq *rq = cpu_rq(cpu); unsigned long flags; raw_spin_rq_lock_irqsave(rq, flags); if (!can_skip_idle_kick(rq) && (cpu_online(cpu) || cpu == cpu_of(this_rq))) resched_curr(rq); raw_spin_rq_unlock_irqrestore(rq, flags); } static void kick_cpus_irq_workfn(struct irq_work *irq_work) { struct rq *this_rq = this_rq(); struct scx_rq *this_scx = &this_rq->scx; struct scx_kick_syncs __rcu *ksyncs_pcpu = __this_cpu_read(scx_kick_syncs); bool should_wait = false; unsigned long *ksyncs; s32 cpu; if (unlikely(!ksyncs_pcpu)) { pr_warn_once("kick_cpus_irq_workfn() called with NULL scx_kick_syncs"); return; } ksyncs = rcu_dereference_bh(ksyncs_pcpu)->syncs; for_each_cpu(cpu, this_scx->cpus_to_kick) { should_wait |= kick_one_cpu(cpu, this_rq, ksyncs); cpumask_clear_cpu(cpu, this_scx->cpus_to_kick); cpumask_clear_cpu(cpu, this_scx->cpus_to_kick_if_idle); } for_each_cpu(cpu, this_scx->cpus_to_kick_if_idle) { kick_one_cpu_if_idle(cpu, this_rq); cpumask_clear_cpu(cpu, this_scx->cpus_to_kick_if_idle); } /* * Can't wait in hardirq — kick_sync can't advance, deadlocking if * CPUs wait for each other. Defer to kick_sync_wait_bal_cb(). */ if (should_wait) { raw_spin_rq_lock(this_rq); this_scx->kick_sync_pending = true; resched_curr(this_rq); raw_spin_rq_unlock(this_rq); } } /** * print_scx_info - print out sched_ext scheduler state * @log_lvl: the log level to use when printing * @p: target task * * If a sched_ext scheduler is enabled, print the name and state of the * scheduler. If @p is on sched_ext, print further information about the task. * * This function can be safely called on any task as long as the task_struct * itself is accessible. While safe, this function isn't synchronized and may * print out mixups or garbages of limited length. */ void print_scx_info(const char *log_lvl, struct task_struct *p) { struct scx_sched *sch; enum scx_enable_state state = scx_enable_state(); const char *all = READ_ONCE(scx_switching_all) ? "+all" : ""; char runnable_at_buf[22] = "?"; struct sched_class *class; unsigned long runnable_at; guard(rcu)(); sch = scx_task_sched_rcu(p); if (!sch) return; /* * Carefully check if the task was running on sched_ext, and then * carefully copy the time it's been runnable, and its state. */ if (copy_from_kernel_nofault(&class, &p->sched_class, sizeof(class)) || class != &ext_sched_class) { printk("%sSched_ext: %s (%s%s)", log_lvl, sch->ops.name, scx_enable_state_str[state], all); return; } if (!copy_from_kernel_nofault(&runnable_at, &p->scx.runnable_at, sizeof(runnable_at))) scnprintf(runnable_at_buf, sizeof(runnable_at_buf), "%+ldms", jiffies_delta_msecs(runnable_at, jiffies)); /* print everything onto one line to conserve console space */ printk("%sSched_ext: %s (%s%s), task: runnable_at=%s", log_lvl, sch->ops.name, scx_enable_state_str[state], all, runnable_at_buf); } static int scx_pm_handler(struct notifier_block *nb, unsigned long event, void *ptr) { struct scx_sched *sch; guard(rcu)(); sch = rcu_dereference(scx_root); if (!sch) return NOTIFY_OK; /* * SCX schedulers often have userspace components which are sometimes * involved in critial scheduling paths. PM operations involve freezing * userspace which can lead to scheduling misbehaviors including stalls. * Let's bypass while PM operations are in progress. */ switch (event) { case PM_HIBERNATION_PREPARE: case PM_SUSPEND_PREPARE: case PM_RESTORE_PREPARE: scx_bypass(sch, true); break; case PM_POST_HIBERNATION: case PM_POST_SUSPEND: case PM_POST_RESTORE: scx_bypass(sch, false); break; } return NOTIFY_OK; } static struct notifier_block scx_pm_notifier = { .notifier_call = scx_pm_handler, }; void __init init_sched_ext_class(void) { s32 cpu, v; /* * The following is to prevent the compiler from optimizing out the enum * definitions so that BPF scheduler implementations can use them * through the generated vmlinux.h. */ WRITE_ONCE(v, SCX_ENQ_WAKEUP | SCX_DEQ_SLEEP | SCX_KICK_PREEMPT | SCX_TG_ONLINE); scx_idle_init_masks(); for_each_possible_cpu(cpu) { struct rq *rq = cpu_rq(cpu); int n = cpu_to_node(cpu); /* local_dsq's sch will be set during scx_root_enable() */ BUG_ON(init_dsq(&rq->scx.local_dsq, SCX_DSQ_LOCAL, NULL)); INIT_LIST_HEAD(&rq->scx.runnable_list); INIT_LIST_HEAD(&rq->scx.ddsp_deferred_locals); BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_kick, GFP_KERNEL, n)); BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_kick_if_idle, GFP_KERNEL, n)); BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_preempt, GFP_KERNEL, n)); BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_wait, GFP_KERNEL, n)); BUG_ON(!zalloc_cpumask_var_node(&rq->scx.cpus_to_sync, GFP_KERNEL, n)); raw_spin_lock_init(&rq->scx.deferred_reenq_lock); INIT_LIST_HEAD(&rq->scx.deferred_reenq_locals); INIT_LIST_HEAD(&rq->scx.deferred_reenq_users); rq->scx.deferred_irq_work = IRQ_WORK_INIT_HARD(deferred_irq_workfn); rq->scx.kick_cpus_irq_work = IRQ_WORK_INIT_HARD(kick_cpus_irq_workfn); if (cpu_online(cpu)) cpu_rq(cpu)->scx.flags |= SCX_RQ_ONLINE; } register_sysrq_key('S', &sysrq_sched_ext_reset_op); register_sysrq_key('D', &sysrq_sched_ext_dump_op); INIT_DELAYED_WORK(&scx_watchdog_work, scx_watchdog_workfn); #ifdef CONFIG_EXT_SUB_SCHED BUG_ON(rhashtable_init(&scx_sched_hash, &scx_sched_hash_params)); #endif /* CONFIG_EXT_SUB_SCHED */ } /******************************************************************************** * Helpers that can be called from the BPF scheduler. */ static bool scx_vet_enq_flags(struct scx_sched *sch, u64 dsq_id, u64 *enq_flags) { bool is_local = dsq_id == SCX_DSQ_LOCAL || (dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON; if (*enq_flags & SCX_ENQ_IMMED) { if (unlikely(!is_local)) { scx_error(sch, "SCX_ENQ_IMMED on a non-local DSQ 0x%llx", dsq_id); return false; } } else if ((sch->ops.flags & SCX_OPS_ALWAYS_ENQ_IMMED) && is_local) { *enq_flags |= SCX_ENQ_IMMED; } return true; } static bool scx_dsq_insert_preamble(struct scx_sched *sch, struct task_struct *p, u64 dsq_id, u64 *enq_flags) { if (!scx_kf_allowed(sch, SCX_KF_ENQUEUE | SCX_KF_DISPATCH)) return false; lockdep_assert_irqs_disabled(); if (unlikely(!p)) { scx_error(sch, "called with NULL task"); return false; } if (unlikely(*enq_flags & __SCX_ENQ_INTERNAL_MASK)) { scx_error(sch, "invalid enq_flags 0x%llx", *enq_flags); return false; } /* see SCX_EV_INSERT_NOT_OWNED definition */ if (unlikely(!scx_task_on_sched(sch, p))) { __scx_add_event(sch, SCX_EV_INSERT_NOT_OWNED, 1); return false; } if (!scx_vet_enq_flags(sch, dsq_id, enq_flags)) return false; return true; } static void scx_dsq_insert_commit(struct scx_sched *sch, struct task_struct *p, u64 dsq_id, u64 enq_flags) { struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; struct task_struct *ddsp_task; ddsp_task = __this_cpu_read(direct_dispatch_task); if (ddsp_task) { mark_direct_dispatch(sch, ddsp_task, p, dsq_id, enq_flags); return; } if (unlikely(dspc->cursor >= sch->dsp_max_batch)) { scx_error(sch, "dispatch buffer overflow"); return; } dspc->buf[dspc->cursor++] = (struct scx_dsp_buf_ent){ .task = p, .qseq = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_QSEQ_MASK, .dsq_id = dsq_id, .enq_flags = enq_flags, }; } __bpf_kfunc_start_defs(); /** * scx_bpf_dsq_insert - Insert a task into the FIFO queue of a DSQ * @p: task_struct to insert * @dsq_id: DSQ to insert into * @slice: duration @p can run for in nsecs, 0 to keep the current value * @enq_flags: SCX_ENQ_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Insert @p into the FIFO queue of the DSQ identified by @dsq_id. It is safe to * call this function spuriously. Can be called from ops.enqueue(), * ops.select_cpu(), and ops.dispatch(). * * When called from ops.select_cpu() or ops.enqueue(), it's for direct dispatch * and @p must match the task being enqueued. * * When called from ops.select_cpu(), @enq_flags and @dsp_id are stored, and @p * will be directly inserted into the corresponding dispatch queue after * ops.select_cpu() returns. If @p is inserted into SCX_DSQ_LOCAL, it will be * inserted into the local DSQ of the CPU returned by ops.select_cpu(). * @enq_flags are OR'd with the enqueue flags on the enqueue path before the * task is inserted. * * When called from ops.dispatch(), there are no restrictions on @p or @dsq_id * and this function can be called upto ops.dispatch_max_batch times to insert * multiple tasks. scx_bpf_dispatch_nr_slots() returns the number of the * remaining slots. scx_bpf_dsq_move_to_local() flushes the batch and resets the * counter. * * This function doesn't have any locking restrictions and may be called under * BPF locks (in the future when BPF introduces more flexible locking). * * @p is allowed to run for @slice. The scheduling path is triggered on slice * exhaustion. If zero, the current residual slice is maintained. If * %SCX_SLICE_INF, @p never expires and the BPF scheduler must kick the CPU with * scx_bpf_kick_cpu() to trigger scheduling. * * Returns %true on successful insertion, %false on failure. On the root * scheduler, %false return triggers scheduler abort and the caller doesn't need * to check the return value. */ __bpf_kfunc bool scx_bpf_dsq_insert___v2(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return false; if (!scx_dsq_insert_preamble(sch, p, dsq_id, &enq_flags)) return false; if (slice) p->scx.slice = slice; else p->scx.slice = p->scx.slice ?: 1; scx_dsq_insert_commit(sch, p, dsq_id, enq_flags); return true; } /* * COMPAT: Will be removed in v6.23 along with the ___v2 suffix. */ __bpf_kfunc void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags, const struct bpf_prog_aux *aux) { scx_bpf_dsq_insert___v2(p, dsq_id, slice, enq_flags, aux); } static bool scx_dsq_insert_vtime(struct scx_sched *sch, struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) { if (!scx_dsq_insert_preamble(sch, p, dsq_id, &enq_flags)) return false; if (slice) p->scx.slice = slice; else p->scx.slice = p->scx.slice ?: 1; p->scx.dsq_vtime = vtime; scx_dsq_insert_commit(sch, p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ); return true; } struct scx_bpf_dsq_insert_vtime_args { /* @p can't be packed together as KF_RCU is not transitive */ u64 dsq_id; u64 slice; u64 vtime; u64 enq_flags; }; /** * __scx_bpf_dsq_insert_vtime - Arg-wrapped vtime DSQ insertion * @p: task_struct to insert * @args: struct containing the rest of the arguments * @args->dsq_id: DSQ to insert into * @args->slice: duration @p can run for in nsecs, 0 to keep the current value * @args->vtime: @p's ordering inside the vtime-sorted queue of the target DSQ * @args->enq_flags: SCX_ENQ_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Wrapper kfunc that takes arguments via struct to work around BPF's 5 argument * limit. BPF programs should use scx_bpf_dsq_insert_vtime() which is provided * as an inline wrapper in common.bpf.h. * * Insert @p into the vtime priority queue of the DSQ identified by * @args->dsq_id. Tasks queued into the priority queue are ordered by * @args->vtime. All other aspects are identical to scx_bpf_dsq_insert(). * * @args->vtime ordering is according to time_before64() which considers * wrapping. A numerically larger vtime may indicate an earlier position in the * ordering and vice-versa. * * A DSQ can only be used as a FIFO or priority queue at any given time and this * function must not be called on a DSQ which already has one or more FIFO tasks * queued and vice-versa. Also, the built-in DSQs (SCX_DSQ_LOCAL and * SCX_DSQ_GLOBAL) cannot be used as priority queues. * * Returns %true on successful insertion, %false on failure. On the root * scheduler, %false return triggers scheduler abort and the caller doesn't need * to check the return value. */ __bpf_kfunc bool __scx_bpf_dsq_insert_vtime(struct task_struct *p, struct scx_bpf_dsq_insert_vtime_args *args, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return false; return scx_dsq_insert_vtime(sch, p, args->dsq_id, args->slice, args->vtime, args->enq_flags); } /* * COMPAT: Will be removed in v6.23. */ __bpf_kfunc void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) { struct scx_sched *sch; guard(rcu)(); sch = rcu_dereference(scx_root); if (unlikely(!sch)) return; #ifdef CONFIG_EXT_SUB_SCHED /* * Disallow if any sub-scheds are attached. There is no way to tell * which scheduler called us, just error out @p's scheduler. */ if (unlikely(!list_empty(&sch->children))) { scx_error(scx_task_sched(p), "__scx_bpf_dsq_insert_vtime() must be used"); return; } #endif scx_dsq_insert_vtime(sch, p, dsq_id, slice, vtime, enq_flags); } __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_enqueue_dispatch) BTF_ID_FLAGS(func, scx_bpf_dsq_insert, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_insert___v2, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, __scx_bpf_dsq_insert_vtime, KF_IMPLICIT_ARGS | KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime, KF_RCU) BTF_KFUNCS_END(scx_kfunc_ids_enqueue_dispatch) static const struct btf_kfunc_id_set scx_kfunc_set_enqueue_dispatch = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_enqueue_dispatch, }; static bool scx_dsq_move(struct bpf_iter_scx_dsq_kern *kit, struct task_struct *p, u64 dsq_id, u64 enq_flags) { struct scx_dispatch_q *src_dsq = kit->dsq, *dst_dsq; struct scx_sched *sch = src_dsq->sched; struct rq *this_rq, *src_rq, *locked_rq; bool dispatched = false; bool in_balance; unsigned long flags; if (!scx_kf_allowed_if_unlocked() && !scx_kf_allowed(sch, SCX_KF_DISPATCH)) return false; if (!scx_vet_enq_flags(sch, dsq_id, &enq_flags)) return false; /* * If the BPF scheduler keeps calling this function repeatedly, it can * cause similar live-lock conditions as consume_dispatch_q(). */ if (unlikely(READ_ONCE(sch->aborting))) return false; if (unlikely(!scx_task_on_sched(sch, p))) { scx_error(sch, "scx_bpf_dsq_move[_vtime]() on %s[%d] but the task belongs to a different scheduler", p->comm, p->pid); return false; } /* * Can be called from either ops.dispatch() locking this_rq() or any * context where no rq lock is held. If latter, lock @p's task_rq which * we'll likely need anyway. */ src_rq = task_rq(p); local_irq_save(flags); this_rq = this_rq(); in_balance = this_rq->scx.flags & SCX_RQ_IN_BALANCE; if (in_balance) { if (this_rq != src_rq) { raw_spin_rq_unlock(this_rq); raw_spin_rq_lock(src_rq); } } else { raw_spin_rq_lock(src_rq); } locked_rq = src_rq; raw_spin_lock(&src_dsq->lock); /* did someone else get to it while we dropped the locks? */ if (nldsq_cursor_lost_task(&kit->cursor, src_rq, src_dsq, p)) { raw_spin_unlock(&src_dsq->lock); goto out; } /* @p is still on $src_dsq and stable, determine the destination */ dst_dsq = find_dsq_for_dispatch(sch, this_rq, dsq_id, task_cpu(p)); /* * Apply vtime and slice updates before moving so that the new time is * visible before inserting into $dst_dsq. @p is still on $src_dsq but * this is safe as we're locking it. */ if (kit->cursor.flags & __SCX_DSQ_ITER_HAS_VTIME) p->scx.dsq_vtime = kit->vtime; if (kit->cursor.flags & __SCX_DSQ_ITER_HAS_SLICE) p->scx.slice = kit->slice; /* execute move */ locked_rq = move_task_between_dsqs(sch, p, enq_flags, src_dsq, dst_dsq); dispatched = true; out: if (in_balance) { if (this_rq != locked_rq) { raw_spin_rq_unlock(locked_rq); raw_spin_rq_lock(this_rq); } } else { raw_spin_rq_unlock_irqrestore(locked_rq, flags); } kit->cursor.flags &= ~(__SCX_DSQ_ITER_HAS_SLICE | __SCX_DSQ_ITER_HAS_VTIME); return dispatched; } __bpf_kfunc_start_defs(); /** * scx_bpf_dispatch_nr_slots - Return the number of remaining dispatch slots * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Can only be called from ops.dispatch(). */ __bpf_kfunc u32 scx_bpf_dispatch_nr_slots(const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return 0; if (!scx_kf_allowed(sch, SCX_KF_DISPATCH)) return 0; return sch->dsp_max_batch - __this_cpu_read(sch->pcpu->dsp_ctx.cursor); } /** * scx_bpf_dispatch_cancel - Cancel the latest dispatch * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Cancel the latest dispatch. Can be called multiple times to cancel further * dispatches. Can only be called from ops.dispatch(). */ __bpf_kfunc void scx_bpf_dispatch_cancel(const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dsp_ctx *dspc; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; if (!scx_kf_allowed(sch, SCX_KF_DISPATCH)) return; dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; if (dspc->cursor > 0) dspc->cursor--; else scx_error(sch, "dispatch buffer underflow"); } /** * scx_bpf_dsq_move_to_local - move a task from a DSQ to the current CPU's local DSQ * @dsq_id: DSQ to move task from. Must be a user-created DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * @enq_flags: %SCX_ENQ_* * * Move a task from the non-local DSQ identified by @dsq_id to the current CPU's * local DSQ for execution with @enq_flags applied. Can only be called from * ops.dispatch(). * * Built-in DSQs (%SCX_DSQ_GLOBAL and %SCX_DSQ_LOCAL*) are not supported as * sources. Local DSQs support reenqueueing (a task can be picked up for * execution, dequeued for property changes, or reenqueued), but the BPF * scheduler cannot directly iterate or move tasks from them. %SCX_DSQ_GLOBAL * is similar but also doesn't support reenqueueing, as it maps to multiple * per-node DSQs making the scope difficult to define; this may change in the * future. * * This function flushes the in-flight dispatches from scx_bpf_dsq_insert() * before trying to move from the specified DSQ. It may also grab rq locks and * thus can't be called under any BPF locks. * * Returns %true if a task has been moved, %false if there isn't any task to * move. */ __bpf_kfunc bool scx_bpf_dsq_move_to_local___v2(u64 dsq_id, u64 enq_flags, const struct bpf_prog_aux *aux) { struct scx_dispatch_q *dsq; struct scx_sched *sch; struct scx_dsp_ctx *dspc; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return false; if (!scx_kf_allowed(sch, SCX_KF_DISPATCH)) return false; if (!scx_vet_enq_flags(sch, SCX_DSQ_LOCAL, &enq_flags)) return false; dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; flush_dispatch_buf(sch, dspc->rq); dsq = find_user_dsq(sch, dsq_id); if (unlikely(!dsq)) { scx_error(sch, "invalid DSQ ID 0x%016llx", dsq_id); return false; } if (consume_dispatch_q(sch, dspc->rq, dsq, enq_flags)) { /* * A successfully consumed task can be dequeued before it starts * running while the CPU is trying to migrate other dispatched * tasks. Bump nr_tasks to tell balance_one() to retry on empty * local DSQ. */ dspc->nr_tasks++; return true; } else { return false; } } /* * COMPAT: ___v2 was introduced in v7.1. Remove this and ___v2 tag in the future. */ __bpf_kfunc bool scx_bpf_dsq_move_to_local(u64 dsq_id, const struct bpf_prog_aux *aux) { return scx_bpf_dsq_move_to_local___v2(dsq_id, 0, aux); } /** * scx_bpf_dsq_move_set_slice - Override slice when moving between DSQs * @it__iter: DSQ iterator in progress * @slice: duration the moved task can run for in nsecs * * Override the slice of the next task that will be moved from @it__iter using * scx_bpf_dsq_move[_vtime](). If this function is not called, the previous * slice duration is kept. */ __bpf_kfunc void scx_bpf_dsq_move_set_slice(struct bpf_iter_scx_dsq *it__iter, u64 slice) { struct bpf_iter_scx_dsq_kern *kit = (void *)it__iter; kit->slice = slice; kit->cursor.flags |= __SCX_DSQ_ITER_HAS_SLICE; } /** * scx_bpf_dsq_move_set_vtime - Override vtime when moving between DSQs * @it__iter: DSQ iterator in progress * @vtime: task's ordering inside the vtime-sorted queue of the target DSQ * * Override the vtime of the next task that will be moved from @it__iter using * scx_bpf_dsq_move_vtime(). If this function is not called, the previous slice * vtime is kept. If scx_bpf_dsq_move() is used to dispatch the next task, the * override is ignored and cleared. */ __bpf_kfunc void scx_bpf_dsq_move_set_vtime(struct bpf_iter_scx_dsq *it__iter, u64 vtime) { struct bpf_iter_scx_dsq_kern *kit = (void *)it__iter; kit->vtime = vtime; kit->cursor.flags |= __SCX_DSQ_ITER_HAS_VTIME; } /** * scx_bpf_dsq_move - Move a task from DSQ iteration to a DSQ * @it__iter: DSQ iterator in progress * @p: task to transfer * @dsq_id: DSQ to move @p to * @enq_flags: SCX_ENQ_* * * Transfer @p which is on the DSQ currently iterated by @it__iter to the DSQ * specified by @dsq_id. All DSQs - local DSQs, global DSQ and user DSQs - can * be the destination. * * For the transfer to be successful, @p must still be on the DSQ and have been * queued before the DSQ iteration started. This function doesn't care whether * @p was obtained from the DSQ iteration. @p just has to be on the DSQ and have * been queued before the iteration started. * * @p's slice is kept by default. Use scx_bpf_dsq_move_set_slice() to update. * * Can be called from ops.dispatch() or any BPF context which doesn't hold a rq * lock (e.g. BPF timers or SYSCALL programs). * * Returns %true if @p has been consumed, %false if @p had already been * consumed, dequeued, or, for sub-scheds, @dsq_id points to a disallowed local * DSQ. */ __bpf_kfunc bool scx_bpf_dsq_move(struct bpf_iter_scx_dsq *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) { return scx_dsq_move((struct bpf_iter_scx_dsq_kern *)it__iter, p, dsq_id, enq_flags); } /** * scx_bpf_dsq_move_vtime - Move a task from DSQ iteration to a PRIQ DSQ * @it__iter: DSQ iterator in progress * @p: task to transfer * @dsq_id: DSQ to move @p to * @enq_flags: SCX_ENQ_* * * Transfer @p which is on the DSQ currently iterated by @it__iter to the * priority queue of the DSQ specified by @dsq_id. The destination must be a * user DSQ as only user DSQs support priority queue. * * @p's slice and vtime are kept by default. Use scx_bpf_dsq_move_set_slice() * and scx_bpf_dsq_move_set_vtime() to update. * * All other aspects are identical to scx_bpf_dsq_move(). See * scx_bpf_dsq_insert_vtime() for more information on @vtime. */ __bpf_kfunc bool scx_bpf_dsq_move_vtime(struct bpf_iter_scx_dsq *it__iter, struct task_struct *p, u64 dsq_id, u64 enq_flags) { return scx_dsq_move((struct bpf_iter_scx_dsq_kern *)it__iter, p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ); } #ifdef CONFIG_EXT_SUB_SCHED /** * scx_bpf_sub_dispatch - Trigger dispatching on a child scheduler * @cgroup_id: cgroup ID of the child scheduler to dispatch * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Allows a parent scheduler to trigger dispatching on one of its direct * child schedulers. The child scheduler runs its dispatch operation to * move tasks from dispatch queues to the local runqueue. * * Returns: true on success, false if cgroup_id is invalid, not a direct * child, or caller lacks dispatch permission. */ __bpf_kfunc bool scx_bpf_sub_dispatch(u64 cgroup_id, const struct bpf_prog_aux *aux) { struct rq *this_rq = this_rq(); struct scx_sched *parent, *child; guard(rcu)(); parent = scx_prog_sched(aux); if (unlikely(!parent)) return false; if (!scx_kf_allowed(parent, SCX_KF_DISPATCH)) return false; child = scx_find_sub_sched(cgroup_id); if (unlikely(!child)) return false; if (unlikely(scx_parent(child) != parent)) { scx_error(parent, "trying to dispatch a distant sub-sched on cgroup %llu", cgroup_id); return false; } return scx_dispatch_sched(child, this_rq, this_rq->scx.sub_dispatch_prev, true); } #endif /* CONFIG_EXT_SUB_SCHED */ __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_dispatch) BTF_ID_FLAGS(func, scx_bpf_dispatch_nr_slots, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dispatch_cancel, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_move_to_local, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_move_to_local___v2, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_slice, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_vtime, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_vtime, KF_RCU) #ifdef CONFIG_EXT_SUB_SCHED BTF_ID_FLAGS(func, scx_bpf_sub_dispatch, KF_IMPLICIT_ARGS) #endif BTF_KFUNCS_END(scx_kfunc_ids_dispatch) static const struct btf_kfunc_id_set scx_kfunc_set_dispatch = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_dispatch, }; __bpf_kfunc_start_defs(); /** * scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Iterate over all of the tasks currently enqueued on the local DSQ of the * caller's CPU, and re-enqueue them in the BPF scheduler. Returns the number of * processed tasks. Can only be called from ops.cpu_release(). */ __bpf_kfunc u32 scx_bpf_reenqueue_local(const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct rq *rq; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return 0; if (!scx_kf_allowed(sch, SCX_KF_CPU_RELEASE)) return 0; rq = cpu_rq(smp_processor_id()); lockdep_assert_rq_held(rq); return reenq_local(sch, rq, SCX_REENQ_ANY); } __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_cpu_release) BTF_ID_FLAGS(func, scx_bpf_reenqueue_local, KF_IMPLICIT_ARGS) BTF_KFUNCS_END(scx_kfunc_ids_cpu_release) static const struct btf_kfunc_id_set scx_kfunc_set_cpu_release = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_cpu_release, }; __bpf_kfunc_start_defs(); /** * scx_bpf_create_dsq - Create a custom DSQ * @dsq_id: DSQ to create * @node: NUMA node to allocate from * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Create a custom DSQ identified by @dsq_id. Can be called from any sleepable * scx callback, and any BPF_PROG_TYPE_SYSCALL prog. */ __bpf_kfunc s32 scx_bpf_create_dsq(u64 dsq_id, s32 node, const struct bpf_prog_aux *aux) { struct scx_dispatch_q *dsq; struct scx_sched *sch; s32 ret; if (unlikely(node >= (int)nr_node_ids || (node < 0 && node != NUMA_NO_NODE))) return -EINVAL; if (unlikely(dsq_id & SCX_DSQ_FLAG_BUILTIN)) return -EINVAL; dsq = kmalloc_node(sizeof(*dsq), GFP_KERNEL, node); if (!dsq) return -ENOMEM; /* * init_dsq() must be called in GFP_KERNEL context. Init it with NULL * @sch and update afterwards. */ ret = init_dsq(dsq, dsq_id, NULL); if (ret) { kfree(dsq); return ret; } rcu_read_lock(); sch = scx_prog_sched(aux); if (sch) { dsq->sched = sch; ret = rhashtable_lookup_insert_fast(&sch->dsq_hash, &dsq->hash_node, dsq_hash_params); } else { ret = -ENODEV; } rcu_read_unlock(); if (ret) { exit_dsq(dsq); kfree(dsq); } return ret; } __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_unlocked) BTF_ID_FLAGS(func, scx_bpf_create_dsq, KF_IMPLICIT_ARGS | KF_SLEEPABLE) BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_slice, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_set_vtime, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_dsq_move_vtime, KF_RCU) BTF_KFUNCS_END(scx_kfunc_ids_unlocked) static const struct btf_kfunc_id_set scx_kfunc_set_unlocked = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_unlocked, }; __bpf_kfunc_start_defs(); /** * scx_bpf_task_set_slice - Set task's time slice * @p: task of interest * @slice: time slice to set in nsecs * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Set @p's time slice to @slice. Returns %true on success, %false if the * calling scheduler doesn't have authority over @p. */ __bpf_kfunc bool scx_bpf_task_set_slice(struct task_struct *p, u64 slice, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!scx_task_on_sched(sch, p))) return false; p->scx.slice = slice; return true; } /** * scx_bpf_task_set_dsq_vtime - Set task's virtual time for DSQ ordering * @p: task of interest * @vtime: virtual time to set * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Set @p's virtual time to @vtime. Returns %true on success, %false if the * calling scheduler doesn't have authority over @p. */ __bpf_kfunc bool scx_bpf_task_set_dsq_vtime(struct task_struct *p, u64 vtime, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!scx_task_on_sched(sch, p))) return false; p->scx.dsq_vtime = vtime; return true; } static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags) { struct rq *this_rq; unsigned long irq_flags; if (!ops_cpu_valid(sch, cpu, NULL)) return; local_irq_save(irq_flags); this_rq = this_rq(); /* * While bypassing for PM ops, IRQ handling may not be online which can * lead to irq_work_queue() malfunction such as infinite busy wait for * IRQ status update. Suppress kicking. */ if (scx_bypassing(sch, cpu_of(this_rq))) goto out; /* * Actual kicking is bounced to kick_cpus_irq_workfn() to avoid nesting * rq locks. We can probably be smarter and avoid bouncing if called * from ops which don't hold a rq lock. */ if (flags & SCX_KICK_IDLE) { struct rq *target_rq = cpu_rq(cpu); if (unlikely(flags & (SCX_KICK_PREEMPT | SCX_KICK_WAIT))) scx_error(sch, "PREEMPT/WAIT cannot be used with SCX_KICK_IDLE"); if (raw_spin_rq_trylock(target_rq)) { if (can_skip_idle_kick(target_rq)) { raw_spin_rq_unlock(target_rq); goto out; } raw_spin_rq_unlock(target_rq); } cpumask_set_cpu(cpu, this_rq->scx.cpus_to_kick_if_idle); } else { cpumask_set_cpu(cpu, this_rq->scx.cpus_to_kick); if (flags & SCX_KICK_PREEMPT) cpumask_set_cpu(cpu, this_rq->scx.cpus_to_preempt); if (flags & SCX_KICK_WAIT) cpumask_set_cpu(cpu, this_rq->scx.cpus_to_wait); } irq_work_queue(&this_rq->scx.kick_cpus_irq_work); out: local_irq_restore(irq_flags); } /** * scx_bpf_kick_cpu - Trigger reschedule on a CPU * @cpu: cpu to kick * @flags: %SCX_KICK_* flags * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Kick @cpu into rescheduling. This can be used to wake up an idle CPU or * trigger rescheduling on a busy CPU. This can be called from any online * scx_ops operation and the actual kicking is performed asynchronously through * an irq work. */ __bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch)) scx_kick_cpu(sch, cpu, flags); } /** * scx_bpf_dsq_nr_queued - Return the number of queued tasks * @dsq_id: id of the DSQ * * Return the number of tasks in the DSQ matching @dsq_id. If not found, * -%ENOENT is returned. */ __bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id) { struct scx_sched *sch; struct scx_dispatch_q *dsq; s32 ret; preempt_disable(); sch = rcu_dereference_sched(scx_root); if (unlikely(!sch)) { ret = -ENODEV; goto out; } if (dsq_id == SCX_DSQ_LOCAL) { ret = READ_ONCE(this_rq()->scx.local_dsq.nr); goto out; } else if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) { s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK; if (ops_cpu_valid(sch, cpu, NULL)) { ret = READ_ONCE(cpu_rq(cpu)->scx.local_dsq.nr); goto out; } } else { dsq = find_user_dsq(sch, dsq_id); if (dsq) { ret = READ_ONCE(dsq->nr); goto out; } } ret = -ENOENT; out: preempt_enable(); return ret; } /** * scx_bpf_destroy_dsq - Destroy a custom DSQ * @dsq_id: DSQ to destroy * * Destroy the custom DSQ identified by @dsq_id. Only DSQs created with * scx_bpf_create_dsq() can be destroyed. The caller must ensure that the DSQ is * empty and no further tasks are dispatched to it. Ignored if called on a DSQ * which doesn't exist. Can be called from any online scx_ops operations. */ __bpf_kfunc void scx_bpf_destroy_dsq(u64 dsq_id) { struct scx_sched *sch; rcu_read_lock(); sch = rcu_dereference(scx_root); if (sch) destroy_dsq(sch, dsq_id); rcu_read_unlock(); } /** * bpf_iter_scx_dsq_new - Create a DSQ iterator * @it: iterator to initialize * @dsq_id: DSQ to iterate * @flags: %SCX_DSQ_ITER_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Initialize BPF iterator @it which can be used with bpf_for_each() to walk * tasks in the DSQ specified by @dsq_id. Iteration using @it only includes * tasks which are already queued when this function is invoked. */ __bpf_kfunc int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id, u64 flags, const struct bpf_prog_aux *aux) { struct bpf_iter_scx_dsq_kern *kit = (void *)it; struct scx_sched *sch; BUILD_BUG_ON(sizeof(struct bpf_iter_scx_dsq_kern) > sizeof(struct bpf_iter_scx_dsq)); BUILD_BUG_ON(__alignof__(struct bpf_iter_scx_dsq_kern) != __alignof__(struct bpf_iter_scx_dsq)); BUILD_BUG_ON(__SCX_DSQ_ITER_ALL_FLAGS & ((1U << __SCX_DSQ_LNODE_PRIV_SHIFT) - 1)); /* * next() and destroy() will be called regardless of the return value. * Always clear $kit->dsq. */ kit->dsq = NULL; sch = scx_prog_sched(aux); if (unlikely(!sch)) return -ENODEV; if (flags & ~__SCX_DSQ_ITER_USER_FLAGS) return -EINVAL; kit->dsq = find_user_dsq(sch, dsq_id); if (!kit->dsq) return -ENOENT; kit->cursor = INIT_DSQ_LIST_CURSOR(kit->cursor, kit->dsq, flags); return 0; } /** * bpf_iter_scx_dsq_next - Progress a DSQ iterator * @it: iterator to progress * * Return the next task. See bpf_iter_scx_dsq_new(). */ __bpf_kfunc struct task_struct *bpf_iter_scx_dsq_next(struct bpf_iter_scx_dsq *it) { struct bpf_iter_scx_dsq_kern *kit = (void *)it; if (!kit->dsq) return NULL; guard(raw_spinlock_irqsave)(&kit->dsq->lock); return nldsq_cursor_next_task(&kit->cursor, kit->dsq); } /** * bpf_iter_scx_dsq_destroy - Destroy a DSQ iterator * @it: iterator to destroy * * Undo scx_iter_scx_dsq_new(). */ __bpf_kfunc void bpf_iter_scx_dsq_destroy(struct bpf_iter_scx_dsq *it) { struct bpf_iter_scx_dsq_kern *kit = (void *)it; if (!kit->dsq) return; if (!list_empty(&kit->cursor.node)) { unsigned long flags; raw_spin_lock_irqsave(&kit->dsq->lock, flags); list_del_init(&kit->cursor.node); raw_spin_unlock_irqrestore(&kit->dsq->lock, flags); } kit->dsq = NULL; } /** * scx_bpf_dsq_peek - Lockless peek at the first element. * @dsq_id: DSQ to examine. * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Read the first element in the DSQ. This is semantically equivalent to using * the DSQ iterator, but is lockfree. Of course, like any lockless operation, * this provides only a point-in-time snapshot, and the contents may change * by the time any subsequent locking operation reads the queue. * * Returns the pointer, or NULL indicates an empty queue OR internal error. */ __bpf_kfunc struct task_struct *scx_bpf_dsq_peek(u64 dsq_id, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dispatch_q *dsq; sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; if (unlikely(dsq_id & SCX_DSQ_FLAG_BUILTIN)) { scx_error(sch, "peek disallowed on builtin DSQ 0x%llx", dsq_id); return NULL; } dsq = find_user_dsq(sch, dsq_id); if (unlikely(!dsq)) { scx_error(sch, "peek on non-existent DSQ 0x%llx", dsq_id); return NULL; } return rcu_dereference(dsq->first_task); } /** * scx_bpf_dsq_reenq - Re-enqueue tasks on a DSQ * @dsq_id: DSQ to re-enqueue * @reenq_flags: %SCX_RENQ_* * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Iterate over all of the tasks currently enqueued on the DSQ identified by * @dsq_id, and re-enqueue them in the BPF scheduler. The following DSQs are * supported: * * - Local DSQs (%SCX_DSQ_LOCAL or %SCX_DSQ_LOCAL_ON | $cpu) * - User DSQs * * Re-enqueues are performed asynchronously. Can be called from anywhere. */ __bpf_kfunc void scx_bpf_dsq_reenq(u64 dsq_id, u64 reenq_flags, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dispatch_q *dsq; guard(preempt)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; if (unlikely(reenq_flags & ~__SCX_REENQ_USER_MASK)) { scx_error(sch, "invalid SCX_REENQ flags 0x%llx", reenq_flags); return; } /* not specifying any filter bits is the same as %SCX_REENQ_ANY */ if (!(reenq_flags & __SCX_REENQ_FILTER_MASK)) reenq_flags |= SCX_REENQ_ANY; dsq = find_dsq_for_dispatch(sch, this_rq(), dsq_id, smp_processor_id()); schedule_dsq_reenq(sch, dsq, reenq_flags, scx_locked_rq()); } /** * scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Iterate over all of the tasks currently enqueued on the local DSQ of the * caller's CPU, and re-enqueue them in the BPF scheduler. Can be called from * anywhere. * * This is now a special case of scx_bpf_dsq_reenq() and may be removed in the * future. */ __bpf_kfunc void scx_bpf_reenqueue_local___v2(const struct bpf_prog_aux *aux) { scx_bpf_dsq_reenq(SCX_DSQ_LOCAL, 0, aux); } __bpf_kfunc_end_defs(); static s32 __bstr_format(struct scx_sched *sch, u64 *data_buf, char *line_buf, size_t line_size, char *fmt, unsigned long long *data, u32 data__sz) { struct bpf_bprintf_data bprintf_data = { .get_bin_args = true }; s32 ret; if (data__sz % 8 || data__sz > MAX_BPRINTF_VARARGS * 8 || (data__sz && !data)) { scx_error(sch, "invalid data=%p and data__sz=%u", (void *)data, data__sz); return -EINVAL; } ret = copy_from_kernel_nofault(data_buf, data, data__sz); if (ret < 0) { scx_error(sch, "failed to read data fields (%d)", ret); return ret; } ret = bpf_bprintf_prepare(fmt, UINT_MAX, data_buf, data__sz / 8, &bprintf_data); if (ret < 0) { scx_error(sch, "format preparation failed (%d)", ret); return ret; } ret = bstr_printf(line_buf, line_size, fmt, bprintf_data.bin_args); bpf_bprintf_cleanup(&bprintf_data); if (ret < 0) { scx_error(sch, "(\"%s\", %p, %u) failed to format", fmt, data, data__sz); return ret; } return ret; } static s32 bstr_format(struct scx_sched *sch, struct scx_bstr_buf *buf, char *fmt, unsigned long long *data, u32 data__sz) { return __bstr_format(sch, buf->data, buf->line, sizeof(buf->line), fmt, data, data__sz); } __bpf_kfunc_start_defs(); /** * scx_bpf_exit_bstr - Gracefully exit the BPF scheduler. * @exit_code: Exit value to pass to user space via struct scx_exit_info. * @fmt: error message format string * @data: format string parameters packaged using ___bpf_fill() macro * @data__sz: @data len, must end in '__sz' for the verifier * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Indicate that the BPF scheduler wants to exit gracefully, and initiate ops * disabling. */ __bpf_kfunc void scx_bpf_exit_bstr(s64 exit_code, char *fmt, unsigned long long *data, u32 data__sz, const struct bpf_prog_aux *aux) { struct scx_sched *sch; unsigned long flags; raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags); sch = scx_prog_sched(aux); if (likely(sch) && bstr_format(sch, &scx_exit_bstr_buf, fmt, data, data__sz) >= 0) scx_exit(sch, SCX_EXIT_UNREG_BPF, exit_code, "%s", scx_exit_bstr_buf.line); raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags); } /** * scx_bpf_error_bstr - Indicate fatal error * @fmt: error message format string * @data: format string parameters packaged using ___bpf_fill() macro * @data__sz: @data len, must end in '__sz' for the verifier * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Indicate that the BPF scheduler encountered a fatal error and initiate ops * disabling. */ __bpf_kfunc void scx_bpf_error_bstr(char *fmt, unsigned long long *data, u32 data__sz, const struct bpf_prog_aux *aux) { struct scx_sched *sch; unsigned long flags; raw_spin_lock_irqsave(&scx_exit_bstr_buf_lock, flags); sch = scx_prog_sched(aux); if (likely(sch) && bstr_format(sch, &scx_exit_bstr_buf, fmt, data, data__sz) >= 0) scx_exit(sch, SCX_EXIT_ERROR_BPF, 0, "%s", scx_exit_bstr_buf.line); raw_spin_unlock_irqrestore(&scx_exit_bstr_buf_lock, flags); } /** * scx_bpf_dump_bstr - Generate extra debug dump specific to the BPF scheduler * @fmt: format string * @data: format string parameters packaged using ___bpf_fill() macro * @data__sz: @data len, must end in '__sz' for the verifier * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * To be called through scx_bpf_dump() helper from ops.dump(), dump_cpu() and * dump_task() to generate extra debug dump specific to the BPF scheduler. * * The extra dump may be multiple lines. A single line may be split over * multiple calls. The last line is automatically terminated. */ __bpf_kfunc void scx_bpf_dump_bstr(char *fmt, unsigned long long *data, u32 data__sz, const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct scx_dump_data *dd = &scx_dump_data; struct scx_bstr_buf *buf = &dd->buf; s32 ret; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; if (raw_smp_processor_id() != dd->cpu) { scx_error(sch, "scx_bpf_dump() must only be called from ops.dump() and friends"); return; } /* append the formatted string to the line buf */ ret = __bstr_format(sch, buf->data, buf->line + dd->cursor, sizeof(buf->line) - dd->cursor, fmt, data, data__sz); if (ret < 0) { dump_line(dd->s, "%s[!] (\"%s\", %p, %u) failed to format (%d)", dd->prefix, fmt, data, data__sz, ret); return; } dd->cursor += ret; dd->cursor = min_t(s32, dd->cursor, sizeof(buf->line)); if (!dd->cursor) return; /* * If the line buf overflowed or ends in a newline, flush it into the * dump. This is to allow the caller to generate a single line over * multiple calls. As ops_dump_flush() can also handle multiple lines in * the line buf, the only case which can lead to an unexpected * truncation is when the caller keeps generating newlines in the middle * instead of the end consecutively. Don't do that. */ if (dd->cursor >= sizeof(buf->line) || buf->line[dd->cursor - 1] == '\n') ops_dump_flush(); } /** * scx_bpf_cpuperf_cap - Query the maximum relative capacity of a CPU * @cpu: CPU of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Return the maximum relative capacity of @cpu in relation to the most * performant CPU in the system. The return value is in the range [1, * %SCX_CPUPERF_ONE]. See scx_bpf_cpuperf_cur(). */ __bpf_kfunc u32 scx_bpf_cpuperf_cap(s32 cpu, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch) && ops_cpu_valid(sch, cpu, NULL)) return arch_scale_cpu_capacity(cpu); else return SCX_CPUPERF_ONE; } /** * scx_bpf_cpuperf_cur - Query the current relative performance of a CPU * @cpu: CPU of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Return the current relative performance of @cpu in relation to its maximum. * The return value is in the range [1, %SCX_CPUPERF_ONE]. * * The current performance level of a CPU in relation to the maximum performance * available in the system can be calculated as follows: * * scx_bpf_cpuperf_cap() * scx_bpf_cpuperf_cur() / %SCX_CPUPERF_ONE * * The result is in the range [1, %SCX_CPUPERF_ONE]. */ __bpf_kfunc u32 scx_bpf_cpuperf_cur(s32 cpu, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (likely(sch) && ops_cpu_valid(sch, cpu, NULL)) return arch_scale_freq_capacity(cpu); else return SCX_CPUPERF_ONE; } /** * scx_bpf_cpuperf_set - Set the relative performance target of a CPU * @cpu: CPU of interest * @perf: target performance level [0, %SCX_CPUPERF_ONE] * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Set the target performance level of @cpu to @perf. @perf is in linear * relative scale between 0 and %SCX_CPUPERF_ONE. This determines how the * schedutil cpufreq governor chooses the target frequency. * * The actual performance level chosen, CPU grouping, and the overhead and * latency of the operations are dependent on the hardware and cpufreq driver in * use. Consult hardware and cpufreq documentation for more information. The * current performance level can be monitored using scx_bpf_cpuperf_cur(). */ __bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return; if (unlikely(perf > SCX_CPUPERF_ONE)) { scx_error(sch, "Invalid cpuperf target %u for CPU %d", perf, cpu); return; } if (ops_cpu_valid(sch, cpu, NULL)) { struct rq *rq = cpu_rq(cpu), *locked_rq = scx_locked_rq(); struct rq_flags rf; /* * When called with an rq lock held, restrict the operation * to the corresponding CPU to prevent ABBA deadlocks. */ if (locked_rq && rq != locked_rq) { scx_error(sch, "Invalid target CPU %d", cpu); return; } /* * If no rq lock is held, allow to operate on any CPU by * acquiring the corresponding rq lock. */ if (!locked_rq) { rq_lock_irqsave(rq, &rf); update_rq_clock(rq); } rq->scx.cpuperf_target = perf; cpufreq_update_util(rq, 0); if (!locked_rq) rq_unlock_irqrestore(rq, &rf); } } /** * scx_bpf_nr_node_ids - Return the number of possible node IDs * * All valid node IDs in the system are smaller than the returned value. */ __bpf_kfunc u32 scx_bpf_nr_node_ids(void) { return nr_node_ids; } /** * scx_bpf_nr_cpu_ids - Return the number of possible CPU IDs * * All valid CPU IDs in the system are smaller than the returned value. */ __bpf_kfunc u32 scx_bpf_nr_cpu_ids(void) { return nr_cpu_ids; } /** * scx_bpf_get_possible_cpumask - Get a referenced kptr to cpu_possible_mask */ __bpf_kfunc const struct cpumask *scx_bpf_get_possible_cpumask(void) { return cpu_possible_mask; } /** * scx_bpf_get_online_cpumask - Get a referenced kptr to cpu_online_mask */ __bpf_kfunc const struct cpumask *scx_bpf_get_online_cpumask(void) { return cpu_online_mask; } /** * scx_bpf_put_cpumask - Release a possible/online cpumask * @cpumask: cpumask to release */ __bpf_kfunc void scx_bpf_put_cpumask(const struct cpumask *cpumask) { /* * Empty function body because we aren't actually acquiring or releasing * a reference to a global cpumask, which is read-only in the caller and * is never released. The acquire / release semantics here are just used * to make the cpumask is a trusted pointer in the caller. */ } /** * scx_bpf_task_running - Is task currently running? * @p: task of interest */ __bpf_kfunc bool scx_bpf_task_running(const struct task_struct *p) { return task_rq(p)->curr == p; } /** * scx_bpf_task_cpu - CPU a task is currently associated with * @p: task of interest */ __bpf_kfunc s32 scx_bpf_task_cpu(const struct task_struct *p) { return task_cpu(p); } /** * scx_bpf_cpu_rq - Fetch the rq of a CPU * @cpu: CPU of the rq * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs */ __bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; if (!ops_cpu_valid(sch, cpu, NULL)) return NULL; if (!sch->warned_deprecated_rq) { printk_deferred(KERN_WARNING "sched_ext: %s() is deprecated; " "use scx_bpf_locked_rq() when holding rq lock " "or scx_bpf_cpu_curr() to read remote curr safely.\n", __func__); sch->warned_deprecated_rq = true; } return cpu_rq(cpu); } /** * scx_bpf_locked_rq - Return the rq currently locked by SCX * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Returns the rq if a rq lock is currently held by SCX. * Otherwise emits an error and returns NULL. */ __bpf_kfunc struct rq *scx_bpf_locked_rq(const struct bpf_prog_aux *aux) { struct scx_sched *sch; struct rq *rq; guard(preempt)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; rq = scx_locked_rq(); if (!rq) { scx_error(sch, "accessing rq without holding rq lock"); return NULL; } return rq; } /** * scx_bpf_cpu_curr - Return remote CPU's curr task * @cpu: CPU of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * Callers must hold RCU read lock (KF_RCU). */ __bpf_kfunc struct task_struct *scx_bpf_cpu_curr(s32 cpu, const struct bpf_prog_aux *aux) { struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) return NULL; if (!ops_cpu_valid(sch, cpu, NULL)) return NULL; return rcu_dereference(cpu_rq(cpu)->curr); } /** * scx_bpf_now - Returns a high-performance monotonically non-decreasing * clock for the current CPU. The clock returned is in nanoseconds. * * It provides the following properties: * * 1) High performance: Many BPF schedulers call bpf_ktime_get_ns() frequently * to account for execution time and track tasks' runtime properties. * Unfortunately, in some hardware platforms, bpf_ktime_get_ns() -- which * eventually reads a hardware timestamp counter -- is neither performant nor * scalable. scx_bpf_now() aims to provide a high-performance clock by * using the rq clock in the scheduler core whenever possible. * * 2) High enough resolution for the BPF scheduler use cases: In most BPF * scheduler use cases, the required clock resolution is lower than the most * accurate hardware clock (e.g., rdtsc in x86). scx_bpf_now() basically * uses the rq clock in the scheduler core whenever it is valid. It considers * that the rq clock is valid from the time the rq clock is updated * (update_rq_clock) until the rq is unlocked (rq_unpin_lock). * * 3) Monotonically non-decreasing clock for the same CPU: scx_bpf_now() * guarantees the clock never goes backward when comparing them in the same * CPU. On the other hand, when comparing clocks in different CPUs, there * is no such guarantee -- the clock can go backward. It provides a * monotonically *non-decreasing* clock so that it would provide the same * clock values in two different scx_bpf_now() calls in the same CPU * during the same period of when the rq clock is valid. */ __bpf_kfunc u64 scx_bpf_now(void) { struct rq *rq; u64 clock; preempt_disable(); rq = this_rq(); if (smp_load_acquire(&rq->scx.flags) & SCX_RQ_CLK_VALID) { /* * If the rq clock is valid, use the cached rq clock. * * Note that scx_bpf_now() is re-entrant between a process * context and an interrupt context (e.g., timer interrupt). * However, we don't need to consider the race between them * because such race is not observable from a caller. */ clock = READ_ONCE(rq->scx.clock); } else { /* * Otherwise, return a fresh rq clock. * * The rq clock is updated outside of the rq lock. * In this case, keep the updated rq clock invalid so the next * kfunc call outside the rq lock gets a fresh rq clock. */ clock = sched_clock_cpu(cpu_of(rq)); } preempt_enable(); return clock; } static void scx_read_events(struct scx_sched *sch, struct scx_event_stats *events) { struct scx_event_stats *e_cpu; int cpu; /* Aggregate per-CPU event counters into @events. */ memset(events, 0, sizeof(*events)); for_each_possible_cpu(cpu) { e_cpu = &per_cpu_ptr(sch->pcpu, cpu)->event_stats; scx_agg_event(events, e_cpu, SCX_EV_SELECT_CPU_FALLBACK); scx_agg_event(events, e_cpu, SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE); scx_agg_event(events, e_cpu, SCX_EV_DISPATCH_KEEP_LAST); scx_agg_event(events, e_cpu, SCX_EV_ENQ_SKIP_EXITING); scx_agg_event(events, e_cpu, SCX_EV_ENQ_SKIP_MIGRATION_DISABLED); scx_agg_event(events, e_cpu, SCX_EV_REENQ_IMMED); scx_agg_event(events, e_cpu, SCX_EV_REENQ_LOCAL_REPEAT); scx_agg_event(events, e_cpu, SCX_EV_REFILL_SLICE_DFL); scx_agg_event(events, e_cpu, SCX_EV_BYPASS_DURATION); scx_agg_event(events, e_cpu, SCX_EV_BYPASS_DISPATCH); scx_agg_event(events, e_cpu, SCX_EV_BYPASS_ACTIVATE); scx_agg_event(events, e_cpu, SCX_EV_INSERT_NOT_OWNED); scx_agg_event(events, e_cpu, SCX_EV_SUB_BYPASS_DISPATCH); } } /* * scx_bpf_events - Get a system-wide event counter to * @events: output buffer from a BPF program * @events__sz: @events len, must end in '__sz'' for the verifier */ __bpf_kfunc void scx_bpf_events(struct scx_event_stats *events, size_t events__sz) { struct scx_sched *sch; struct scx_event_stats e_sys; rcu_read_lock(); sch = rcu_dereference(scx_root); if (sch) scx_read_events(sch, &e_sys); else memset(&e_sys, 0, sizeof(e_sys)); rcu_read_unlock(); /* * We cannot entirely trust a BPF-provided size since a BPF program * might be compiled against a different vmlinux.h, of which * scx_event_stats would be larger (a newer vmlinux.h) or smaller * (an older vmlinux.h). Hence, we use the smaller size to avoid * memory corruption. */ events__sz = min(events__sz, sizeof(*events)); memcpy(events, &e_sys, events__sz); } #ifdef CONFIG_CGROUP_SCHED /** * scx_bpf_task_cgroup - Return the sched cgroup of a task * @p: task of interest * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs * * @p->sched_task_group->css.cgroup represents the cgroup @p is associated with * from the scheduler's POV. SCX operations should use this function to * determine @p's current cgroup as, unlike following @p->cgroups, * @p->sched_task_group is protected by @p's rq lock and thus atomic w.r.t. all * rq-locked operations. Can be called on the parameter tasks of rq-locked * operations. The restriction guarantees that @p's rq is locked by the caller. */ __bpf_kfunc struct cgroup *scx_bpf_task_cgroup(struct task_struct *p, const struct bpf_prog_aux *aux) { struct task_group *tg = p->sched_task_group; struct cgroup *cgrp = &cgrp_dfl_root.cgrp; struct scx_sched *sch; guard(rcu)(); sch = scx_prog_sched(aux); if (unlikely(!sch)) goto out; if (!scx_kf_allowed_on_arg_tasks(sch, __SCX_KF_RQ_LOCKED, p)) goto out; cgrp = tg_cgrp(tg); out: cgroup_get(cgrp); return cgrp; } #endif /* CONFIG_CGROUP_SCHED */ __bpf_kfunc_end_defs(); BTF_KFUNCS_START(scx_kfunc_ids_any) BTF_ID_FLAGS(func, scx_bpf_task_set_slice, KF_IMPLICIT_ARGS | KF_RCU); BTF_ID_FLAGS(func, scx_bpf_task_set_dsq_vtime, KF_IMPLICIT_ARGS | KF_RCU); BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued) BTF_ID_FLAGS(func, scx_bpf_destroy_dsq) BTF_ID_FLAGS(func, scx_bpf_dsq_peek, KF_IMPLICIT_ARGS | KF_RCU_PROTECTED | KF_RET_NULL) BTF_ID_FLAGS(func, scx_bpf_dsq_reenq, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_reenqueue_local___v2, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, bpf_iter_scx_dsq_new, KF_IMPLICIT_ARGS | KF_ITER_NEW | KF_RCU_PROTECTED) BTF_ID_FLAGS(func, bpf_iter_scx_dsq_next, KF_ITER_NEXT | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_iter_scx_dsq_destroy, KF_ITER_DESTROY) BTF_ID_FLAGS(func, scx_bpf_exit_bstr, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_error_bstr, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_cpuperf_set, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_nr_node_ids) BTF_ID_FLAGS(func, scx_bpf_nr_cpu_ids) BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask, KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask, KF_ACQUIRE) BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE) BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) BTF_ID_FLAGS(func, scx_bpf_cpu_rq, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_IMPLICIT_ARGS | KF_RET_NULL) BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED) BTF_ID_FLAGS(func, scx_bpf_now) BTF_ID_FLAGS(func, scx_bpf_events) #ifdef CONFIG_CGROUP_SCHED BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_IMPLICIT_ARGS | KF_RCU | KF_ACQUIRE) #endif BTF_KFUNCS_END(scx_kfunc_ids_any) static const struct btf_kfunc_id_set scx_kfunc_set_any = { .owner = THIS_MODULE, .set = &scx_kfunc_ids_any, }; static int __init scx_init(void) { int ret; /* * kfunc registration can't be done from init_sched_ext_class() as * register_btf_kfunc_id_set() needs most of the system to be up. * * Some kfuncs are context-sensitive and can only be called from * specific SCX ops. They are grouped into BTF sets accordingly. * Unfortunately, BPF currently doesn't have a way of enforcing such * restrictions. Eventually, the verifier should be able to enforce * them. For now, register them the same and make each kfunc explicitly * check using scx_kf_allowed(). */ if ((ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_enqueue_dispatch)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_dispatch)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_cpu_release)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_unlocked)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_unlocked)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &scx_kfunc_set_any)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &scx_kfunc_set_any)) || (ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &scx_kfunc_set_any))) { pr_err("sched_ext: Failed to register kfunc sets (%d)\n", ret); return ret; } ret = scx_idle_init(); if (ret) { pr_err("sched_ext: Failed to initialize idle tracking (%d)\n", ret); return ret; } ret = register_bpf_struct_ops(&bpf_sched_ext_ops, sched_ext_ops); if (ret) { pr_err("sched_ext: Failed to register struct_ops (%d)\n", ret); return ret; } ret = register_pm_notifier(&scx_pm_notifier); if (ret) { pr_err("sched_ext: Failed to register PM notifier (%d)\n", ret); return ret; } scx_kset = kset_create_and_add("sched_ext", &scx_uevent_ops, kernel_kobj); if (!scx_kset) { pr_err("sched_ext: Failed to create /sys/kernel/sched_ext\n"); return -ENOMEM; } ret = sysfs_create_group(&scx_kset->kobj, &scx_global_attr_group); if (ret < 0) { pr_err("sched_ext: Failed to add global attributes\n"); return ret; } if (!alloc_cpumask_var(&scx_bypass_lb_donee_cpumask, GFP_KERNEL) || !alloc_cpumask_var(&scx_bypass_lb_resched_cpumask, GFP_KERNEL)) { pr_err("sched_ext: Failed to allocate cpumasks\n"); return -ENOMEM; } return 0; } __initcall(scx_init);