[PATCH v25 2/9] sched: Minimise repeated sched_proxy_exec() checking

John Stultz
2026-03-13T02:30:30Z

Peter noted: Compilers are really bad (as in they utterly refuse)
optimizing (even when marked with __pure) the static branch
things, and will happily emit multiple identical in a row.

So pull out the one obvious sched_proxy_exec() branch in
__schedule() and remove some of the 'implicit' ones in that
path.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: John Stultz <jstultz@google.com>
---
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Qais Yousef <qyousef@layalina.io>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: kuyo chang <kuyo.chang@mediatek.com>
Cc: hupu <hupu.gm@gmail.com>
Cc: kernel-team@android.com
---
kernel/sched/core.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d86d648a75a4b..84c61496fa263 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6597,11 +6597,7 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
struct mutex *mutex;

/* Follow blocked_on chain. */
- for (p = donor; task_is_blocked(p); p = owner) {
- mutex = p->blocked_on;
- /* Something changed in the chain, so pick again */
- if (!mutex)
- return NULL;
+ for (p = donor; (mutex = p->blocked_on); p = owner) {
/*
* By taking mutex->wait_lock we hold off concurrent mutex_unlock()
* and ensure @owner sticks around.
@@ -6832,12 +6828,14 @@ static void __sched notrace __schedule(int sched_mode)
next = pick_next_task(rq, rq->donor, &rf);
rq_set_donor(rq, next);
rq->next_class = next->sched_class;
- if (unlikely(task_is_blocked(next))) {
- next = find_proxy_task(rq, next, &rf);
- if (!next)
- goto pick_again;
- if (next == rq->idle)
- goto keep_resched;
+ if (sched_proxy_exec()) {
+ if (unlikely(next->blocked_on)) {
+ next = find_proxy_task(rq, next, &rf);
+ if (!next)
+ goto pick_again;
+ if (next == rq->idle)
+ goto keep_resched;
+ }
}
picked:
clear_tsk_need_resched(prev);
--
2.53.0.880.g73c4285caa-goog