Re: [PATCH 19/24] sched/eevdf: Fixup PELT vs DELAYED_DEQUEUE

Valentin Schneider
2024-08-13T12:44:01Z

On 27/07/24 12:27, Peter Zijlstra wrote:
> Note that tasks that are kept on the runqueue to burn off negative
> lag, are not in fact runnable anymore, they'll get dequeued the moment
> they get picked.
>
> As such, don't count this time towards runnable.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> kernel/sched/fair.c | 2 ++
> kernel/sched/sched.h | 6 ++++++
> 2 files changed, 8 insertions(+)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5388,6 +5388,7 @@ dequeue_entity(struct cfs_rq *cfs_rq, st
> if (cfs_rq->next == se)
> cfs_rq->next = NULL;
> se->sched_delayed = 1;
> + update_load_avg(cfs_rq, se, 0);

Shouldn't this be before setting ->sched_delayed? accumulate_sum() should
see the time delta as spent being runnable.

> return false;
> }
> }
> @@ -6814,6 +6815,7 @@ requeue_delayed_entity(struct sched_enti
> }
>
> se->sched_delayed = 0;
> + update_load_avg(cfs_rq, se, 0);

Ditto on the ordering

> }
>
> /*
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -816,6 +816,9 @@ static inline void se_update_runnable(st
>
> static inline long se_runnable(struct sched_entity *se)
> {
> + if (se->sched_delayed)
> + return false;
> +

Per __update_load_avg_se(), delayed-dequeue entities are still ->on_rq, so
their load signal will increase. Do we want a similar helper for the @load
input of ___update_load_sum()?

> if (entity_is_task(se))
> return !!se->on_rq;
> else
> @@ -830,6 +833,9 @@ static inline void se_update_runnable(st
>
> static inline long se_runnable(struct sched_entity *se)
> {
> + if (se->sched_delayed)
> + return false;
> +
> return !!se->on_rq;
> }
>