linux-kernel - [PATCH 2/2] sched/uclamp: Add uclamp_is

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Message-ID: <20250213091554.2593-2-xuewen.yan@unisoc.com>
Date: Thu, 13 Feb 2025 17:15:54 +0800
From: Xuewen Yan <xuewen.yan@...soc.com>
To: <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
        <vincent.guittot@...aro.org>
CC: <dietmar.eggemann@....com>, <rostedt@...dmis.org>, <bsegall@...gle.com>,
        <mgorman@...e.de>, <vschneid@...hat.com>, <qyousef@...alina.io>,
        <ke.wang@...soc.com>, <di.shen@...soc.com>, <xuewen.yan94@...il.com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/2] sched/uclamp: Add uclamp_is_used() check before enable it

Because the static_branch_enable() would get the cpus_read_lock(),
and sometimes users may frequently set the uclamp value of tasks,
and the uclamp_validate() would call the static_branch_enable()
frequently, so add the uclamp_is_used() check to prevent calling
the cpus_read_lock() frequently.

Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
---
 kernel/sched/syscalls.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index 456d339be98f..d718fddadb03 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -368,7 +368,8 @@ static int uclamp_validate(struct task_struct *p,
 	 * blocking operation which obviously cannot be done while holding
 	 * scheduler locks.
 	 */
-	static_branch_enable(&sched_uclamp_used);
+	if (!uclamp_is_used())
+		static_branch_enable(&sched_uclamp_used);
 
 	return 0;
 }
-- 
2.25.1