On Mon, May 11, 2020 at 09:13:20PM +0200 Vincent Guittot wrote:
> Although not exactly identical, unthrottle_cfs_rq() and enqueue_task_fair()
> are quite close and follow the same sequence for enqueuing an entity in the
> cfs hierarchy. Modify unthrottle_cfs_rq() to use the same pattern as
> enqueue_task_fair(). This fixes a problem already faced with the latter and
> add an optimization in the last for_each_sched_entity loop.
>
> Fixes: fe61468b2cb (sched/fair: Fix enqueue_task_fair warning)
> Reported-by Tao Zhou <zohooou...@zoho.com.cn>
> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
> ---
>
> This path applies on top of 20200507203612.gf19...@lorien.usersys.redhat.com
> and fixes similar problem for unthrottle_cfs_rq()
>
> kernel/sched/fair.c | 37 ++++++++++++++++++++++++++++---------
> 1 file changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e2450c2e0747..4b73518aa25c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4803,26 +4803,44 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
> idle_task_delta = cfs_rq->idle_h_nr_running;
> for_each_sched_entity(se) {
> if (se->on_rq)
> - enqueue = 0;
> + break;
> + cfs_rq = cfs_rq_of(se);
> + enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
>
> + cfs_rq->h_nr_running += task_delta;
> + cfs_rq->idle_h_nr_running += idle_task_delta;
> +
> + /* end evaluation on encountering a throttled cfs_rq */
> + if (cfs_rq_throttled(cfs_rq))
> + goto unthrottle_throttle;
> + }
> +
> + for_each_sched_entity(se) {
> cfs_rq = cfs_rq_of(se);
> - if (enqueue) {
> - enqueue_entity(cfs_rq, se, ENQUEUE_WAKEUP);
> - } else {
> - update_load_avg(cfs_rq, se, 0);
> - se_update_runnable(se);
> - }
> +
> + update_load_avg(cfs_rq, se, UPDATE_TG);
> + se_update_runnable(se);
>
> cfs_rq->h_nr_running += task_delta;
> cfs_rq->idle_h_nr_running += idle_task_delta;
>
> +
> + /* end evaluation on encountering a throttled cfs_rq */
> if (cfs_rq_throttled(cfs_rq))
> - break;
> + goto unthrottle_throttle;
> +
> + /*
> + * One parent has been throttled and cfs_rq removed from the
> + * list. Add it back to not break the leaf list.
> + */
> + if (throttled_hierarchy(cfs_rq))
> + list_add_leaf_cfs_rq(cfs_rq);
> }
>
> if (!se)
> add_nr_running(rq, task_delta);
>
> +unthrottle_throttle:
> /*
> * The cfs_rq_throttled() breaks in the above iteration can result in
> * incomplete leaf list maintenance, resulting in triggering the
> @@ -4831,7 +4849,8 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
> for_each_sched_entity(se) {
> cfs_rq = cfs_rq_of(se);
>
> - list_add_leaf_cfs_rq(cfs_rq);
> + if (list_add_leaf_cfs_rq(cfs_rq))
> + break;
> }
>
> assert_list_leaf_cfs_rq(rq);
> --
> 2.17.1
>
I ran my reproducer test with this one as well. As expected, since
the first patch fixed the issue I was seeing and I wasn't hitting
the assert here anyway, I didn't hit the assert.
But I also didn't hit any other issues, new or old.
It makes sense to use the same logic flow here as enqueue_task_fair.
Reviewed-by: Phil Auld <pa...@redhat.com>
Cheers,
Phil
--
