The following commit has been merged into the sched/core branch of tip: Commit-ID: 4bc45824149ea83a1e293c674e7f542b8127afb6 Gitweb: https://git.kernel.org/tip/4bc45824149ea83a1e293c674e7f542b8127afb6 Author: Xuewen Yan <xuewen.yan@xxxxxxxxxx> AuthorDate: Wed, 19 Feb 2025 17:37:47 +08:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Sat, 15 Mar 2025 10:28:50 +01:00 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: Xuewen Yan <xuewen.yan@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Reviewed-by: Christian Loehle <christian.loehle@xxxxxxx> Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx> Link: https://lore.kernel.org/r/20250219093747.2612-2-xuewen.yan@xxxxxxxxxx --- kernel/sched/core.c | 6 +++--- kernel/sched/sched.h | 14 ++++++++++++++ kernel/sched/syscalls.c | 2 +- 3 files changed, 18 insertions(+), 4 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 45daa41..03d7b63 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -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)(); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 8d42d3c..0212a0c 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -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) { diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c index 9f40348..c326de1 100644 --- a/kernel/sched/syscalls.c +++ b/kernel/sched/syscalls.c @@ -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; }
![]() |