user/sven/linux.git/include/linux/workqueue.h, branch v6.9.4

workqueue: Drain BH work items on hot-unplugged CPUs

2024-02-29T21:51:24Z

Boqun pointed out that workqueues aren't handling BH work items on offlined CPUs. Unlike tasklet which transfers out the pending tasks from CPUHP_SOFTIRQ_DEAD, BH workqueue would just leave them pending which is problematic. Note that this behavior is specific to BH workqueues as the non-BH per-CPU workers just become unbound when the CPU goes offline. This patch fixes the issue by draining the pending BH work items from an offlined CPU from CPUHP_SOFTIRQ_DEAD. Because work items carry more context, it's not as easy to transfer the pending work items from one pool to another. Instead, run BH work items which execute the offlined pools on an online CPU. Note that this assumes that no further BH work items will be queued on the offlined CPUs. This assumption is shared with tasklet and should be fine for conversions. However, this issue also exists for per-CPU workqueues which will just keep executing work items queued after CPU offline on unbound workers and workqueue should reject per-CPU and BH work items queued on offline CPUs. This will be addressed separately later. Signed-off-by: Tejun Heo Reported-and-reviewed-by: Boqun Feng Link: http://lkml.kernel.org/r/Zdvw0HdSXcU3JZ4g@boqun-archlinux

workqueue: Introduce from_work() helper for cleaner callback declarations

2024-02-27T19:38:26Z

To streamline the transition from tasklets to worqueues, a new helper function, from_work(), is introduced. This helper, inspired by existing from_() patterns, utilizes container_of() and eliminates the redundancy of declaring variable types, leading to more concise and readable code. The modified code snippet demonstrates the enhanced clarity achieved with from_wq(): void callback(struct work_struct *w) { - struct some_data_structure *local = container_of(w, struct some_data_structure, work); + struct some_data_structure *local = from_work(local, w, work); This change aims to facilitate a smoother transition and uphold code quality standards. Based on: git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git disable_work-v3 Signed-off-by: Allen Pais Signed-off-by: Tejun Heo

workqueue: Clean up enum work_bits and related constants

2024-02-21T05:36:14Z

The bits of work->data are used for a few different purposes. How the bits are used is determined by enum work_bits. The planned disable/enable support will add another use, so let's clean it up a bit in preparation. - Let WORK_STRUCT_*_BIT's values be determined by enum definition order. - Deliminate different bit sections the same way using SHIFT and BITS values. - Rename __WORK_OFFQ_CANCELING to WORK_OFFQ_CANCELING_BIT for consistency. - Introduce WORK_STRUCT_PWQ_SHIFT and replace WORK_STRUCT_FLAG_MASK and WORK_STRUCT_WQ_DATA_MASK with WQ_STRUCT_PWQ_MASK for clarity. - Improve documentation. No functional changes. Signed-off-by: Tejun Heo Reviewed-by: Lai Jiangshan

workqueue: Implement workqueue_set_min_active()

2024-02-09T21:13:59Z

Since 5797b1c18919 ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues"), unbound workqueues have separate min_active which sets the number of interdependent work items that can be handled. This value is currently initialized to WQ_DFL_MIN_ACTIVE which is 8. This isn't high enough for some users, let's add an interface to adjust the setting. Signed-off-by: Tejun Heo

workqueue: Don't implicitly make UNBOUND workqueues w/ @max_active==1 ordered

2024-02-06T00:19:10Z

5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered") automoatically promoted UNBOUND workqueues w/ @max_active==1 to ordered workqueues because UNBOUND workqueues w/ @max_active==1 used to be the way to create ordered workqueues and the new NUMA support broke it. These problems can be subtle and the fact that they can only trigger on NUMA machines made them even more difficult to debug. However, overloading the UNBOUND allocation interface this way creates other issues. It's difficult to tell whether a given workqueue actually needs to be ordered and users that legitimately want a min concurrency level wq unexpectedly gets an ordered one instead. With planned UNBOUND workqueue udpates to improve execution locality and more prevalence of chiplet designs which can benefit from such improvements, this isn't a state we wanna be in forever. There aren't that many UNBOUND w/ @max_active==1 users in the tree and the preceding patches audited all and converted them to alloc_ordered_workqueue() as appropriate. This patch removes the implicit promotion of UNBOUND w/ @max_active==1 workqueues to ordered ones. v2: v1 patch incorrectly dropped !list_empty(&wq->pwqs) condition in apply_workqueue_attrs_locked() which spuriously triggers WARNING and fails workqueue creation. Fix it. Signed-off-by: Tejun Heo Reported-by: kernel test robot Link: https://lore.kernel.org/oe-lkp/202304251050.45a5df1f-oliver.sang@intel.com

workqueue: Implement BH workqueues to eventually replace tasklets

2024-02-04T21:28:06Z

The only generic interface to execute asynchronously in the BH context is tasklet; however, it's marked deprecated and has some design flaws such as the execution code accessing the tasklet item after the execution is complete which can lead to subtle use-after-free in certain usage scenarios and less-developed flush and cancel mechanisms. This patch implements BH workqueues which share the same semantics and features of regular workqueues but execute their work items in the softirq context. As there is always only one BH execution context per CPU, none of the concurrency management mechanisms applies and a BH workqueue can be thought of as a convenience wrapper around softirq. Except for the inability to sleep while executing and lack of max_active adjustments, BH workqueues and work items should behave the same as regular workqueues and work items. Currently, the execution is hooked to tasklet[_hi]. However, the goal is to convert all tasklet users over to BH workqueues. Once the conversion is complete, tasklet can be removed and BH workqueues can directly take over the tasklet softirqs. system_bh[_highpri]_wq are added. As queue-wide flushing doesn't exist in tasklet, all existing tasklet users should be able to use the system BH workqueues without creating their own workqueues. v3: - Add missing interrupt.h include. v2: - Instead of using tasklets, hook directly into its softirq action functions - tasklet[_hi]_action(). This is slightly cheaper and closer to the eventual code structure we want to arrive at. Suggested by Lai. - Lai also pointed out several places which need NULL worker->task handling or can use clarification. Updated. Signed-off-by: Tejun Heo Suggested-by: Linus Torvalds Link: http://lkml.kernel.org/r/CAHk-=wjDW53w4-YcSmgKC5RruiRLHmJ1sXeYdp_ZgVoBw=5byA@mail.gmail.com Tested-by: Allen Pais Reviewed-by: Lai Jiangshan

workqueue: Implement system-wide nr_active enforcement for unbound workqueues

2024-01-29T18:11:25Z

A pool_workqueue (pwq) represents the connection between a workqueue and a worker_pool. One of the roles that a pwq plays is enforcement of the max_active concurrency limit. Before 636b927eba5b ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues"), there was one pwq per each CPU for per-cpu workqueues and per each NUMA node for unbound workqueues, which was a natural result of per-cpu workqueues being served by per-cpu pools and unbound by per-NUMA pools. In terms of max_active enforcement, this was, while not perfect, workable. For per-cpu workqueues, it was fine. For unbound, it wasn't great in that NUMA machines would get max_active that's multiplied by the number of nodes but didn't cause huge problems because NUMA machines are relatively rare and the node count is usually pretty low. However, cache layouts are more complex now and sharing a worker pool across a whole node didn't really work well for unbound workqueues. Thus, a series of commits culminating on 8639ecebc9b1 ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues") implemented more flexible affinity mechanism for unbound workqueues which enables using e.g. last-level-cache aligned pools. In the process, 636b927eba5b ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues") made unbound workqueues use per-cpu pwqs like per-cpu workqueues. While the change was necessary to enable more flexible affinity scopes, this came with the side effect of blowing up the effective max_active for unbound workqueues. Before, the effective max_active for unbound workqueues was multiplied by the number of nodes. After, by the number of CPUs. 636b927eba5b ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues") claims that this should generally be okay. It is okay for users which self-regulates concurrency level which are the vast majority; however, there are enough use cases which actually depend on max_active to prevent the level of concurrency from going bonkers including several IO handling workqueues that can issue a work item for each in-flight IO. With targeted benchmarks, the misbehavior can easily be exposed as reported in http://lkml.kernel.org/r/dbu6wiwu3sdhmhikb2w6lns7b27gbobfavhjj57kwi2quafgwl@htjcc5oikcr3. Unfortunately, there is no way to express what these use cases need using per-cpu max_active. A CPU may issue most of in-flight IOs, so we don't want to set max_active too low but as soon as we increase max_active a bit, we can end up with unreasonable number of in-flight work items when many CPUs issue IOs at the same time. ie. The acceptable lowest max_active is higher than the acceptable highest max_active. Ideally, max_active for an unbound workqueue should be system-wide so that the users can regulate the total level of concurrency regardless of node and cache layout. The reasons workqueue hasn't implemented that yet are: - One max_active enforcement decouples from pool boundaires, chaining execution after a work item finishes requires inter-pool operations which would require lock dancing, which is nasty. - Sharing a single nr_active count across the whole system can be pretty expensive on NUMA machines. - Per-pwq enforcement had been more or less okay while we were using per-node pools. It looks like we no longer can avoid decoupling max_active enforcement from pool boundaries. This patch implements system-wide nr_active mechanism with the following design characteristics: - To avoid sharing a single counter across multiple nodes, the configured max_active is split across nodes according to the proportion of each workqueue's online effective CPUs per node. e.g. A node with twice more online effective CPUs will get twice higher portion of max_active. - Workqueue used to be able to process a chain of interdependent work items which is as long as max_active. We can't do this anymore as max_active is distributed across the nodes. Instead, a new parameter min_active is introduced which determines the minimum level of concurrency within a node regardless of how max_active distribution comes out to be. It is set to the smaller of max_active and WQ_DFL_MIN_ACTIVE which is 8. This can lead to higher effective max_weight than configured and also deadlocks if a workqueue was depending on being able to handle chains of interdependent work items that are longer than 8. I believe these should be fine given that the number of CPUs in each NUMA node is usually higher than 8 and work item chain longer than 8 is pretty unlikely. However, if these assumptions turn out to be wrong, we'll need to add an interface to adjust min_active. - Each unbound wq has an array of struct wq_node_nr_active which tracks per-node nr_active. When its pwq wants to run a work item, it has to obtain the matching node's nr_active. If over the node's max_active, the pwq is queued on wq_node_nr_active->pending_pwqs. As work items finish, the completion path round-robins the pending pwqs activating the first inactive work item of each, which involves some pool lock dancing and kicking other pools. It's not the simplest code but doesn't look too bad. v4: - wq_adjust_max_active() updated to invoke wq_update_node_max_active(). - wq_adjust_max_active() is now protected by wq->mutex instead of wq_pool_mutex. v3: - wq_node_max_active() used to calculate per-node max_active on the fly based on system-wide CPU online states. Lai pointed out that this can lead to skewed distributions for workqueues with restricted cpumasks. Update the max_active distribution to use per-workqueue effective online CPU counts instead of system-wide and cache the calculation results in node_nr_active->max. v2: - wq->min/max_active now uses WRITE/READ_ONCE() as suggested by Lai. Signed-off-by: Tejun Heo Reported-by: Naohiro Aota Link: http://lkml.kernel.org/r/dbu6wiwu3sdhmhikb2w6lns7b27gbobfavhjj57kwi2quafgwl@htjcc5oikcr3 Fixes: 636b927eba5b ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues") Reviewed-by: Lai Jiangshan

workqueue: Break up enum definitions and give names to the types

2024-01-26T21:55:50Z

workqueue is collecting different sorts of enums into a single unnamed enum type which can increase confusion around enum width. Also, unnamed enums can't be accessed from BPF. Let's break up enum definitions according to their purposes and give them type names. Signed-off-by: Tejun Heo

Merge tag 'header_cleanup-2024-01-10' of https://evilpiepirate.org/git/bcachefs

2024-01-11T00:43:55Z

Pull header cleanups from Kent Overstreet: "The goal is to get sched.h down to a type only header, so the main thing happening in this patchset is splitting out various _types.h headers and dependency fixups, as well as moving some things out of sched.h to better locations. This is prep work for the memory allocation profiling patchset which adds new sched.h interdepencencies" * tag 'header_cleanup-2024-01-10' of https://evilpiepirate.org/git/bcachefs: (51 commits) Kill sched.h dependency on rcupdate.h kill unnecessary thread_info.h include Kill unnecessary kernel.h include preempt.h: Kill dependency on list.h rseq: Split out rseq.h from sched.h LoongArch: signal.c: add header file to fix build error restart_block: Trim includes lockdep: move held_lock to lockdep_types.h sem: Split out sem_types.h uidgid: Split out uidgid_types.h seccomp: Split out seccomp_types.h refcount: Split out refcount_types.h uapi/linux/resource.h: fix include x86/signal: kill dependency on time.h syscall_user_dispatch.h: split out *_types.h mm_types_task.h: Trim dependencies Split out irqflags_types.h ipc: Kill bogus dependency on spinlock.h shm: Slim down dependencies workqueue: Split out workqueue_types.h ...

workqueue: Split out workqueue_types.h

2023-12-21T00:26:31Z

More sched.h dependency culling - this lets us kill a rhashtable-types.h dependency on workqueue.h. Signed-off-by: Kent Overstreet