sched/util_est: Simplify condition for util_est_{en,de}queue()

To prevent double enqueue/dequeue of the util-est for sched_delayed tasks,
commit 729288bc6856 ("kernel/sched: Fix util_est accounting for DELAY_DEQUEUE")
added the corresponding check. This check excludes double en/dequeue during
task migration and priority changes.

In fact, these conditions can be simplified.

For util_est_dequeue, we know that sched_delayed flag is set in dequeue_entity.
When the task is sleeping, we need to call util_est_dequeue to subtract
util-est from the cfs_rq. At this point, sched_delayed has not yet been set.
If we find that sched_delayed is already set, it indicates that this task
has already called dequeue_task_fair once. In this case, there is no need to
call util_est_dequeue again. Therefore, simply checking the sched_delayed flag
should be sufficient to prevent unnecessary util_est updates during the dequeue.

For util_est_enqueue, our goal is to add the util_est to the cfs_rq
when task enqueue. However, we don't want to add the util_est of a
sched_delayed task to the cfs_rq because the task is sleeping.
Therefore, we can exclude the util_est_enqueue for sched_delayed tasks
by checking the sched_delayed flag. However, when waking up a delayed task,
the sched_delayed flag is cleared after util_est_enqueue. As a result,
if we only check the sched_delayed flag, we would miss the util_est_enqueue.
Since waking up a sched_delayed task calls enqueue_task with the ENQUEUE_DELAYED flag,
we can determine whether to call util_est_enqueue by checking if the
enqueue_flag contains ENQUEUE_DELAYED.

Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Link: https://lore.kernel.org/r/20250417043457.10632-2-xuewen.yan@unisoc.com

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b00f16700f9c5b46f04e01c822a857dd8b520197..a028c294aef31ceab7b5fd4a75c7842ecc1dcd9b 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6936,7 +6936,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
         * Let's add the task's estimated utilization to the cfs_rq's
         * estimated utilization, before we update schedutil.
         */
-       if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags & ENQUEUE_RESTORE))))
+       if (!p->se.sched_delayed || (flags & ENQUEUE_DELAYED))
                util_est_enqueue(&rq->cfs, p);
 
        if (flags & ENQUEUE_DELAYED) {
@@ -7178,7 +7178,7 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
  */
 static bool dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 {
-       if (!(p->se.sched_delayed && (task_on_rq_migrating(p) || (flags & DEQUEUE_SAVE))))
+       if (!p->se.sched_delayed)
                util_est_dequeue(&rq->cfs, p);
 
        util_est_update(&rq->cfs, p, flags & DEQUEUE_SLEEP);