Commit 4bc45824 authored by Xuewen Yan's avatar Xuewen Yan Committed by Ingo Molnar
Browse files

sched/uclamp: Optimize sched_uclamp_used static key enabling 



Repeat calls of static_branch_enable() to an already enabled
static key introduce overhead, because it calls cpus_read_lock().

Users may frequently set the uclamp value of tasks, triggering
the repeat enabling of the sched_uclamp_used static key.

Optimize this and avoid repeat calls to static_branch_enable()
by checking whether it's enabled already.

[ mingo: Rewrote the changelog for legibility ]

Signed-off-by: default avatarXuewen Yan <xuewen.yan@unisoc.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarChristian Loehle <christian.loehle@arm.com>
Reviewed-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20250219093747.2612-2-xuewen.yan@unisoc.com
parent 5fca5a4c

kernel/sched/core.c

+3 −3
Original line number Diff line number Diff line
@@ -1941,12 +1941,12 @@ static int sysctl_sched_uclamp_handler(const struct ctl_table *table, int write, 
	}



	if (update_root_tg) {

		static_branch_enable(&sched_uclamp_used);

		sched_uclamp_enable();

		uclamp_update_root_tg();

	}



	if (old_min_rt != sysctl_sched_uclamp_util_min_rt_default) {

		static_branch_enable(&sched_uclamp_used);

		sched_uclamp_enable();

		uclamp_sync_util_min_rt_default();

	}
@@ -9294,7 +9294,7 @@ static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf, 
	if (req.ret)

		return req.ret;



	static_branch_enable(&sched_uclamp_used);

	sched_uclamp_enable();



	guard(mutex)(&uclamp_mutex);

	guard(rcu)();

kernel/sched/sched.h

+14 −0
Original line number Diff line number Diff line
@@ -3407,6 +3407,18 @@ static inline bool uclamp_is_used(void) 
	return static_branch_likely(&sched_uclamp_used);

}



/*

 * Enabling static branches would get the cpus_read_lock(),

 * check whether uclamp_is_used before enable it to avoid always

 * calling cpus_read_lock(). Because we never disable this

 * static key once enable it.

 */

static inline void sched_uclamp_enable(void)

{

	if (!uclamp_is_used())

		static_branch_enable(&sched_uclamp_used);

}



static inline unsigned long uclamp_rq_get(struct rq *rq,

					  enum uclamp_id clamp_id)

{
@@ -3486,6 +3498,8 @@ static inline bool uclamp_is_used(void) 
	return false;

}



static inline void sched_uclamp_enable(void) {}



static inline unsigned long

uclamp_rq_get(struct rq *rq, enum uclamp_id clamp_id)

{

kernel/sched/syscalls.c

+1 −1
Original line number Diff line number Diff line
@@ -368,7 +368,7 @@ 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);

	sched_uclamp_enable();



	return 0;

}