linux-kernel - Re: [PATCH 1/7] posix-cpu-timers: don't account cpu timer after stopped thread runtime accounting

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Date:	Fri, 10 May 2013 22:40:09 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Olivier Langlois <olivier@...llion01.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/7] posix-cpu-timers: don't account cpu timer after
 stopped thread runtime accounting

On Fri, May 10, 2013 at 8:17 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> On Mon, May 06, 2013 at 11:16:40PM -0400, Olivier Langlois wrote:
>> On Tue, 2013-05-07 at 01:47 +0200, Frederic Weisbecker wrote:
>> > On Fri, May 03, 2013 at 12:47:42AM -0400, kosaki.motohiro@...il.com wrote:
>> > > From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>> > >
>> > > When tsk->signal->cputimer->running is 1, signal->cputimer and
>> > > tsk->sum_sched_runtime increase at the same pace because update_curr()
>> > > increases both accounting.
>> > >
>> > > However, there is one exception. When thread exiting, __exit_signal() turns
>> > > over task's sum_shced_runtime to sig->sum_sched_runtime, but it doesn't stop
>> > > signal->cputimer accounting.
>> > >
>> > > This inconsistency makes POSIX timer wake up too early. This patch fixes it.
>> > >
>> > > Cc: Thomas Gleixner <tglx@...utronix.de>
>> > > Cc: Frederic Weisbecker <fweisbec@...il.com>
>> > > Cc: Ingo Molnar <mingo@...nel.org>
>> > > Acked-by: Peter Zijlstra <peterz@...radead.org>
>> > > Signed-off-by: Olivier Langlois <olivier@...llion01.com>
>> > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>> > > ---
>> > >  kernel/sched/stats.h |    7 +++++++
>> > >  1 files changed, 7 insertions(+), 0 deletions(-)
>> > >
>> > > diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
>> > > index 2ef90a5..5a0cfc4 100644
>> > > --- a/kernel/sched/stats.h
>> > > +++ b/kernel/sched/stats.h
>> > > @@ -225,6 +225,13 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
>> > >       if (!cputimer->running)
>> > >               return;
>> > >
>> > > +     /*
>> > > +      * After turning over se.sum_exec_runtime to sig->sum_sched_runtime
>> > > +      * in __exit_signal(), we must not account exec_runtime for consistency.
>> > > +      */
>
> Please just precise the nature of that consistency: the fact we want CLOCK_PROCESS_CPUTIME_ID
> clock and timer to be consistent.

typo? This patch fixes an inconsistency between a thread cputime and a
process cputime.

How is this?

/*
* After turning over se.sum_exec_runtime to sig->sum_sched_runtime
* in __exit_signal(), a per-thread cputime of the thread will be lost. We
* must not account exec_runtime here too because we need to keep
* consistent cputime between per-thread and per-process. Otherwise,
* the inconsistency is observable when single thread program run.
*/
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