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

[Frederic Weisbecker <fweisbec@gmail.com>]

On Fri, May 03, 2013 at 12:47:42AM -0400, kosaki.motohiro@gmail.com wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@jp.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@linutronix.de>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Acked-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Olivier Langlois <olivier@trillion01.com>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.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.
> +	 */
> +	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().

> +
>  	raw_spin_lock(&cputimer->lock);
>  	cputimer->cputime.sum_exec_runtime += ns;
>  	raw_spin_unlock(&cputimer->lock);
> -- 
> 1.7.1
>