linux-kernel - [PATCH] sched,trace: Allow tracing the preemption decision on wakeup

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Date:	Thu, 14 Mar 2013 10:48:39 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	mingo@...nel.org, tglx <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] sched,trace: Allow tracing the preemption decision on wakeup

Thomas noted that we do the wakeup preemption check after the wakeup
trace point, this means the tracepoint cannot test/report this decision;
which is rather important for latency sensitive workloads. Therefore
move the tracepoint after doing the preemption check.

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b36635e..849deb9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1288,8 +1288,8 @@ static void ttwu_activate(struct rq *rq, struct task_struct *p, int en_flags)
 static void
 ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
 {
-	trace_sched_wakeup(p, true);
 	check_preempt_curr(rq, p, wake_flags);
+	trace_sched_wakeup(p, true);
 
 	p->state = TASK_RUNNING;
 #ifdef CONFIG_SMP


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