linux-kernel - Re: [PATCH]sched/stop_task: Do not account zero delta_exec in put_prev_task

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Message-ID: <1360869932.23152.51.camel@gandalf.local.home>
Date:	Thu, 14 Feb 2013 14:25:32 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Kirill Tkhai <tkhai@...dex.ru>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH]sched/stop_task: Do not account zero delta_exec in
 put_prev_task_stop

On Wed, 2013-02-13 at 15:15 +0900, Namhyung Kim wrote:
> ---
> >  kernel/sched/stop_task.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
> > index da5eb5b..78d0458 100644
> > --- a/kernel/sched/stop_task.c
> > +++ b/kernel/sched/stop_task.c
> > @@ -58,8 +58,8 @@ static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
> >  	u64 delta_exec;
> >  
> >  	delta_exec = rq->clock_task - curr->se.exec_start;
> > -	if (unlikely((s64)delta_exec < 0))
> > -		delta_exec = 0;
> > +	if (unlikely((s64)delta_exec <= 0))
> > +		return;
> 
> It seems it needs to update curr->se.exec_start then.
> 

Ah, if it's less than zero, it does.

A better patch would be:

	if (unlikely((s64)delta_exec <= 0)) {
		curr->se.exec_start = rq->clock_task;
		return;
	}

Thanks!

-- Steve


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