Re: [PATCH v2 1/3] process cputimer is moving faster than its corresponding clock

KOSAKI Motohiro
2013-04-29T05:06:53Z

(4/27/13 12:40 AM), 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().
>
> Ideally, you should postpone the release_task() call after the
> final context switch to get all the stats added but this is
> more complex to achieve.
>
> In other words, this is slowing down the cputimer so it keep the same
> pace than the process clock but in fact, what should be done is to
> speed up the process clock by adding the missing stats to it.
>
> 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);
> }

I'm confused. glibc's rt/tst-cputimer1 doesn't have thread exiting code. I have
no seen any issue in this accounting.