linux-kernel - [tip: sched/core] sched/util_est: Simplify condition for util_est

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Message-ID: <174782921810.406.7735731150435046147.tip-bot2@tip-bot2>
Date: Wed, 21 May 2025 12:06:58 -0000
From: "tip-bot2 for Xuewen Yan" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Xuewen Yan <xuewen.yan@...soc.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/util_est: Simplify condition for
 util_est_{en,de}queue()

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     0212696a844631a923aa6cedd74ebbb3cf434e51
Gitweb:        https://git.kernel.org/tip/0212696a844631a923aa6cedd74ebbb3cf434e51
Author:        Xuewen Yan <xuewen.yan@...soc.com>
AuthorDate:    Thu, 17 Apr 2025 12:34:56 +08:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 21 May 2025 13:57:38 +02:00

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@...soc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>
Link: https://lore.kernel.org/r/20250417043457.10632-2-xuewen.yan@unisoc.com
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b00f167..a028c29 100644
--- 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);