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SubjectRe: [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@trillion01.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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