Messages in this thread Patch in this message | | | Date | Mon, 06 Dec 2010 20:58:44 -0500 | From | Steven Rostedt <> | Subject | [RFC][PATCH 10/10] sched: Remove unlikely() from ttwu_post_activation |
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From: Steven Rostedt <srostedt@redhat.com>
The unlikely() used in ttwu_post_activation() tests if the rq->idle_stamp is set. But since this is for a wakeup, and wakeups happen when tasks block on IO, and blocking tasks on IO may put the system into idle, this can actually be a common occurence.
Running the annotated branch profiler on an average desktop running firefox, evolution, xchat and distcc, the report shows:
correct incorrect % Function File Line ------- --------- - -------- ---- ---- 34884862 146110926 80 ttwu_post_activation sched.c 2309
80% of the time, this unlikely is incorrect. Best not to assume what the result is, and just remove the branch annotation.
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> --- kernel/sched.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c index 269a045..6d24b2e 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2458,7 +2458,7 @@ static inline void ttwu_post_activation(struct task_struct *p, struct rq *rq, if (p->sched_class->task_woken) p->sched_class->task_woken(rq, p); - if (unlikely(rq->idle_stamp)) { + if (rq->idle_stamp) { u64 delta = rq->clock - rq->idle_stamp; u64 max = 2*sysctl_sched_migration_cost; -- 1.7.2.3
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