user/sven/linux.git/kernel/rcu/tree.c, branch v3.16.52

rcu: Use rcu_gp_kthread_wake() to wake up grace period kthreads

2014-11-27T11:22:08Z

commit 2aa792e6faf1a00f5accf1f69e87e11a390ba2cd upstream. The rcu_gp_kthread_wake() function checks for three conditions before waking up grace period kthreads: * Is the thread we are trying to wake up the current thread? * Are the gp_flags zero? (all threads wait on non-zero gp_flags condition) * Is there no thread created for this flavour, hence nothing to wake up? If any one of these condition is true, we do not call wake_up(). It was found that there are quite a few avoidable wake ups both during idle time and under stress induced by rcutorture. Idle: Total:66000, unnecessary:66000, case1:61827, case2:66000, case3:0 Total:68000, unnecessary:68000, case1:63696, case2:68000, case3:0 rcutorture: Total:254000, unnecessary:254000, case1:199913, case2:254000, case3:0 Total:256000, unnecessary:256000, case1:201784, case2:256000, case3:0 Here case{1-3} are the cases listed above. We can avoid these wake ups by using rcu_gp_kthread_wake() to conditionally wake up the grace period kthreads. There is a comment about an implied barrier supplied by the wake_up() logic. This barrier is necessary for the awakened thread to see the updated ->gp_flags. This flag is always being updated with the root node lock held. Also, the awakened thread tries to acquire the root node lock before reading ->gp_flags because of which there is proper ordering. Hence this commit tries to avoid calling wake_up() whenever we can by using rcu_gp_kthread_wake() function. Signed-off-by: Pranith Kumar CC: Mathieu Desnoyers Signed-off-by: Paul E. McKenney Signed-off-by: Luis Henriques

rcu: Reduce overhead of cond_resched() checks for RCU

2014-06-23T18:19:32Z

Commit ac1bea85781e (Make cond_resched() report RCU quiescent states) fixed a problem where a CPU looping in the kernel with but one runnable task would give RCU CPU stall warnings, even if the in-kernel loop contained cond_resched() calls. Unfortunately, in so doing, it introduced performance regressions in Anton Blanchard's will-it-scale "open1" test. The problem appears to be not so much the increased cond_resched() path length as an increase in the rate at which grace periods complete, which increased per-update grace-period overhead. This commit takes a different approach to fixing this bug, mainly by moving the RCU-visible quiescent state from cond_resched() to rcu_note_context_switch(), and by further reducing the check to a simple non-zero test of a single per-CPU variable. However, this approach requires that the force-quiescent-state processing send resched IPIs to the offending CPUs. These will be sent only once the grace period has reached an age specified by the boot/sysfs parameter rcutree.jiffies_till_sched_qs, or once the grace period reaches an age halfway to the point at which RCU CPU stall warnings will be emitted, whichever comes first. Reported-by: Dave Hansen Signed-off-by: Paul E. McKenney Cc: Andi Kleen Cc: Christoph Lameter Cc: Mike Galbraith Cc: Eric Dumazet Reviewed-by: Josh Triplett [ paulmck: Made rcu_momentary_dyntick_idle() as suggested by the ktest build robot. Also fixed smp_mb() comment as noted by Oleg Nesterov. ] Merge with e552592e (Reduce overhead of cond_resched() checks for RCU) Signed-off-by: Paul E. McKenney

Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next

2014-06-03T19:57:53Z

Pull core locking updates from Ingo Molnar: "The main changes in this cycle were: - reduced/streamlined smp_mb__*() interface that allows more usecases and makes the existing ones less buggy, especially in rarer architectures - add rwsem implementation comments - bump up lockdep limits" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (33 commits) rwsem: Add comments to explain the meaning of the rwsem's count field lockdep: Increase static allocations arch: Mass conversion of smp_mb__*() arch,doc: Convert smp_mb__*() arch,xtensa: Convert smp_mb__*() arch,x86: Convert smp_mb__*() arch,tile: Convert smp_mb__*() arch,sparc: Convert smp_mb__*() arch,sh: Convert smp_mb__*() arch,score: Convert smp_mb__*() arch,s390: Convert smp_mb__*() arch,powerpc: Convert smp_mb__*() arch,parisc: Convert smp_mb__*() arch,openrisc: Convert smp_mb__*() arch,mn10300: Convert smp_mb__*() arch,mips: Convert smp_mb__*() arch,metag: Convert smp_mb__*() arch,m68k: Convert smp_mb__*() arch,m32r: Convert smp_mb__*() arch,ia64: Convert smp_mb__*() ...

rcu: Variable name changed in tree_plugin.h and used in tree.c

2014-05-14T18:41:04Z

The variable and struct both having the name "rcu_state" confuses sparse in some situations, so this commit changes the variable to "rcu_state_p" in order to avoid this confusion. This also makes things easier for human readers. Signed-off-by: Uma Sharma [ paulmck: Changed the declaration and several additional uses. ] Signed-off-by: Paul E. McKenney

Merge branches 'doc.2014.04.29a', 'fixes.2014.04.29a' and 'torture.2014.05.14a' into HEAD

2014-05-14T17:57:31Z

doc.2014.04.29a: Documentation updates. fixes.2014.04.29a: Miscellaneous fixes. torture.2014.05.14a: RCU/Lock torture tests.

rcutorture: Export RCU grace-period kthread wait state to rcutorture

2014-05-14T16:46:09Z

This commit allows rcutorture to print additional state for the RCU grace-period kthreads in cases where RCU seems reluctant to start a new grace period. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcutorture: Add forward-progress checking for writer

2014-05-13T18:18:18Z

The rcutorture output currently does not distinguish between stalls in the RCU implementation and stalls in the rcu_torture_writer() kthreads. This commit therefore adds some diagnostics to help distinguish between these two conditions, at least for the non-SRCU implementations. (SRCU does not provide evidence of update-side forward progress by design.) Signed-off-by: Paul E. McKenney

rcu: Replace __this_cpu_ptr() uses with raw_cpu_ptr()

2014-04-29T15:45:35Z

__this_cpu_ptr is being phased out. One special case is increment_cpu_stall_ticks(). A per cpu variable is incremented so use raw_cpu_inc(). Cc: Dipankar Sarma Signed-off-by: Christoph Lameter Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Remove duplicate resched_cpu() declaration

2014-04-29T15:45:29Z

Signed-off-by: Pranith Kumar Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett

rcu: Merge rcu_sched_force_quiescent_state() with rcu_force_quiescent_state()

2014-04-29T15:45:07Z

This patch merges the function rcu_force_quiescent_state() with rcu_sched_force_quiescent_state(), using the rcu_state pointer. Firstly, the rcu_sched_force_quiescent_state() function is deleted from the file kernel/rcu/tree.c. Also, the rcu_force_quiescent_state() function that was calling force_quiescent_state with the argument rcu_preempt_state pointer was deleted as well. The new function that combines the old ones uses the rcu_state pointer and is located after rcu_batches_completed_bh() in kernel/rcu/tree.c. Signed-off-by: Andreea-Cristina Bernat Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett