linux-kernel - [PATCH v1] sched/uclamp: Skip uclamp_rq_dec() for non-final dequeue of delayed tasks

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Message-Id: <20250701093407.211500-1-zhangzihuan@kylinos.cn>
Date: Tue,  1 Jul 2025 17:34:07 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: xuewen.yan@...soc.com,
	vincent.guittot@...aro.org,
	mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com
Cc: rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	hongyan.xia2@....com,
	linux-kernel@...r.kernel.org,
	ke.wang@...soc.com,
	di.shen@...soc.com,
	xuewen.yan94@...il.com,
	kprateek.nayak@....com,
	kuyo.chang@...iatek.com,
	juju.sung@...iatek.com,
	qyousef@...alina.io,
	Zihuan Zhang <zhangzihuan@...inos.cn>
Subject: [PATCH v1] sched/uclamp: Skip uclamp_rq_dec() for non-final dequeue of delayed tasks

Currently, uclamp_rq_inc() skips updating the clamp aggregation for
delayed tasks unless ENQUEUE_DELAYED is set, to ensure we only track the
real enqueue of a task that was previously marked as sched_delayed.

However, the corresponding uclamp_rq_dec() path only checks
sched_delayed, and misses the DEQUEUE_DELAYED flag. As a result, we may
skip dec for a delayed task that is now being truly dequeued, leading to
uclamp aggregation mismatch.

This patch makes uclamp_rq_dec() consistent with uclamp_rq_inc() by
checking both sched_delayed and DEQUEUE_DELAYED, ensuring correct
accounting symmetry.

Fixes: 90ca9410dab2 ("sched/uclamp: Align uclamp and util_est and call before freq update")
Signed-off-by: Zihuan Zhang <zhangzihuan@...inos.cn>
---
 kernel/sched/core.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8988d38d46a3..99f1542cff7d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1781,7 +1781,7 @@ static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p, int flags
 		rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
 }
 
-static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
+static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p, int flags)
 {
 	enum uclamp_id clamp_id;
 
@@ -1797,7 +1797,8 @@ static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
 	if (unlikely(!p->sched_class->uclamp_enabled))
 		return;
 
-	if (p->se.sched_delayed)
+	/* Skip dec if this is a delayed task not being truly dequeued */
+	if (p->se.sched_delayed && !(flags & DEQUEUE_DELAYED))
 		return;
 
 	for_each_clamp_id(clamp_id)
@@ -2039,7 +2040,7 @@ static void __init init_uclamp(void)
 
 #else /* !CONFIG_UCLAMP_TASK */
 static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p, int flags) { }
-static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
+static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p, int flags) { }
 static inline void uclamp_fork(struct task_struct *p) { }
 static inline void uclamp_post_fork(struct task_struct *p) { }
 static inline void init_uclamp(void) { }
@@ -2112,7 +2113,7 @@ inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
 	 * Must be before ->dequeue_task() because ->dequeue_task() can 'fail'
 	 * and mark the task ->sched_delayed.
 	 */
-	uclamp_rq_dec(rq, p);
+	uclamp_rq_dec(rq, p, flags);
 	return p->sched_class->dequeue_task(rq, p, flags);
 }
 
-- 
2.25.1