[tip: sched/core] sched: Minimise repeated sched_proxy_exec() checking

[tip-bot2 for John Stultz]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     37341ec573da7c16fdd45222b1bfb7b421dbdbcb
Gitweb:        https://git.kernel.org/tip/37341ec573da7c16fdd45222b1bfb7b421dbdbcb
Author:        John Stultz <jstultz@xxxxxxxxxx>
AuthorDate:    Tue, 24 Mar 2026 19:13:17 
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 03 Apr 2026 14:23:38 +02:00

sched: Minimise repeated sched_proxy_exec() checking

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@xxxxxxxxxxxxx>
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Link: https://patch.msgid.link/20260324191337.1841376-3-jstultz@xxxxxxxxxx
---
 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 2974168..f3306d3 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 @@ pick_again:
 	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);