linux-kernel - Re: [PATCH 4/8] sched/core: Skip wakeup when task is already running.

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Date:	Tue, 15 Apr 2014 15:53:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
Cc:	rostedt@...dmis.org, fweisbec@...il.com, mingo@...hat.com,
	acme@...stprotocols.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/8] sched/core: Skip wakeup when task is already running.

On Tue, Apr 15, 2014 at 09:32:53PM +0900, Dongsheng Yang wrote:
> From: Dongsheng <yangds.fnst@...fujitsu.com>
> 
> It is pointless to wake up a running task. Currently, we can
> see it in perf sched latency.
> 
> Signed-off-by: Dongsheng <yangds.fnst@...fujitsu.com>
> ---
>  kernel/sched/core.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 268a45e..fc6b644 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1416,6 +1416,9 @@ 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)
>  {
> +	if (p->state == TASK_RUNNING)
> +		return;
> +
>  	check_preempt_curr(rq, p, wake_flags);
>  	trace_sched_wakeup(p, true);
>  


How can you get there with ->state == RUNNING? try_to_wake_up*() bail
when !(->state & state).
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