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

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Date:	Tue, 7 May 2013 17:24:44 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Olivier Langlois <olivier@...llion01.com>,
	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

2013/5/7 KOSAKI Motohiro <kosaki.motohiro@...il.com>:
>>> +     /*
>>> +      * After turning over se.sum_exec_runtime to sig->sum_sched_runtime
>>> +      * in __exit_signal(), we must not account exec_runtime for consistency.
>>> +      */
>>> +     if (unlikely(!tsk->sighand))
>>> +             return;
>>
>> Ok, if we want the clock and timer to be consistent, do we also want the same check in
>> account_group_user_time() and account_group_system_time()? The task can still account
>> a tick after autoreaping itself between release_task() and the final schedule().
>
> You are right.
>
> That said, current the man pages don't describe this linux specific
> extensions. So, nobody
> (glibc, ltp, and me) tested them. Please give me a couple of days.
> I'll test and fix this features
> too.
>
> timer_create(2): http://man7.org/linux/man-pages/man2/timer_create.2.html

Ah, indeed timer_create() seem to only create CPUCLOCK_SCHED timers. So that
issue with timer_gettime becoming asynchonous with clock_gettime can't happen
with PROF and VIRT clocks

I see itimers can use those clocks. But there don't seem to be a
similar issue with
getitimer/setitimer as they don't have matching clock reads.

Thanks.
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