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| author |   Davidlohr Bueso <dave@stgolabs.net> | 2018-12-02 21:31:30 -0800 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2019-01-21 11:18:50 +0100 |
| commit | 87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec (patch) | |
| tree | a68291414ab3e040c7701ed26c361fe7c9f2d13d /kernel/sched | |
| parent | Merge branch 'locking/urgent' into locking/core, to pick up dependent fixes (diff) | |
| download | linux-dev-87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec.tar.xz linux-dev-87ff19cb2f1aa55a5d8b691e6690cc059a59d2ec.zip | |
sched/wake_q: Add branch prediction hint to wake_q_add() cmpxchg
The cmpxchg() will fail when the task is already in the process
of waking up, and as such is an extremely rare occurrence.
Micro-optimize the call and put an unlikely() around it.
To no surprise, when using CONFIG_PROFILE_ANNOTATED_BRANCHES
under a number of workloads the incorrect rate was a mere 1-2%.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yongji Xie <elohimes@gmail.com>
Cc: andrea.parri@amarulasolutions.com
Cc: lilin24@baidu.com
Cc: liuqi16@baidu.com
Cc: nixun@baidu.com
Cc: xieyongji@baidu.com
Cc: yuanlinsi01@baidu.com
Cc: zhangyu31@baidu.com
Link: https://lkml.kernel.org/r/20181203053130.gwkw6kg72azt2npb@linux-r8p5
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/core.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d8d76a65cfdd..b05eef7d7a1f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -421,7 +421,7 @@ void wake_q_add(struct wake_q_head *head, struct task_struct *task) * state, even in the failed case, an explicit smp_mb() must be used. */ smp_mb__before_atomic(); - if (cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)) + if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL))) return; get_task_struct(task); |