lkml.org 
[lkml]   [2020]   [Mar]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH v2] sched/fair : fix reordering of enqueue_task_fair
Date
Vincent Guittot <vincent.guittot@linaro.org> writes:

> Even when a cgroup is throttled, the group se of a child cgroup can still
> be enqueued and its gse->on_rq stays true. When a task is enqueued on such
> child, we still have to update the load_avg and increase
> h_nr_running of the throttled cfs. Nevertheless, the 1st
> for_each_sched_entity loop is skipped because of gse->on_rq == true and the
> 2nd loop because the cfs is throttled whereas we have to update both
> load_avg with the old h_nr_running and increase h_nr_running in such case.
> Note that the update of load_avg will effectively happen only once in order
> to sync up to the throttled time. Next call for updating load_avg will stop
> early because the clock stays unchanged.
>
> Fixes: 6d4d22468dae ("sched/fair: Reorder enqueue/dequeue_task_fair path")
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> kernel/sched/fair.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index fcc968669aea..5b232d261842 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5431,16 +5431,16 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> for_each_sched_entity(se) {
> cfs_rq = cfs_rq_of(se);
>
> - /* end evaluation on encountering a throttled cfs_rq */
> - if (cfs_rq_throttled(cfs_rq))
> - goto enqueue_throttle;
> -
> update_load_avg(cfs_rq, se, UPDATE_TG);
> se_update_runnable(se);
> update_cfs_group(se);
>
> cfs_rq->h_nr_running++;
> cfs_rq->idle_h_nr_running += idle_h_nr_running;
> +
> + /* end evaluation on encountering a throttled cfs_rq */
> + if (cfs_rq_throttled(cfs_rq))
> + goto enqueue_throttle;
> }
>
> enqueue_throttle:


I think there's an equivalent issue on dequeue as well, though that's
much rarer to trigger (but still possible). I think the same fix works
there too?

\
 
 \ /
  Last update: 2020-03-05 19:40    [W:0.079 / U:3.968 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site