[RFC][PATCH 10/10] sched: Remove unlikely() from ttwu_post_activation

Steven Rostedt
2010-12-07T02:14:00Z

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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