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

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Message-ID: <1363262445.25967.30.camel@gandalf.local.home>
Date:	Thu, 14 Mar 2013 08:00:45 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, tglx <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>, Paul Turner <pjt@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched,trace: Allow tracing the preemption decision on
 wakeup

On Thu, 2013-03-14 at 10:48 +0100, Peter Zijlstra wrote:
> 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>

Acked-by: Steven Rostedt <rostedt@...dmis.org>

> ---
>  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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