linux-kernel - Re: [PATCH v3 1/3] posix_timers: do not account group_exec

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Message-ID: <20130506231835.GC1225@somewhere>
Date:	Tue, 7 May 2013 01:18:37 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Olivier Langlois <olivier@...vierlanglois.net>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, schwidefsky@...ibm.com,
	Steven Rostedt <rostedt@...dmis.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] posix_timers: do not account group_exec_runtime
 for dying autoreaped tasks

On Mon, Apr 29, 2013 at 02:04:09PM -0400, Olivier Langlois wrote:
> 
> 
> Forbids the cputimer to drift ahead of its process clock by
> blocking its update when a tick occurs while a autoreaping task
> is currently in do_exit() between the call to release_task() and
> its final call to schedule().
> 
> Any task stats update after having called release_task() will
> be lost because they are added to the global process stats located
> in the signal struct from release_task().

I wonder if this is real problem that the clock is ahead of the timer.
Have you seen any issue in practice with this? Or may be it's a
guarantee that the posix clock should provide wrt. to the timer?

thanks.

> 
> Signed-off-by: Olivier Langlois <olivier@...llion01.com>
> ---
>  kernel/sched/fair.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 7a33e59..52d7b10 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -708,7 +708,15 @@ static void update_curr(struct cfs_rq *cfs_rq)
>  
>                 trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
>                 cpuacct_charge(curtask, delta_exec);
> -               account_group_exec_runtime(curtask, delta_exec);
> +               /*
> +                * Do not update the cputimer if the task is already released by
> +                * release_task().
> +                *
> +                * it would preferable to defer the autoreap release_task
> +                * after the last context switch but harder to do.
> +                */
> +               if (likely(curtask->sighand))
> +                       account_group_exec_runtime(curtask, delta_exec);
>         }
>  
>         account_cfs_rq_runtime(cfs_rq, delta_exec);
> -- 
> 1.8.2.1
> 
> 
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