linux-kernel - [PATCH] sched: Optimize core cookie matching check

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Message-ID: <20251105152538.470586-1-sieberf@amazon.com>
Date: Wed, 5 Nov 2025 17:25:37 +0200
From: Fernand Sieber <sieberf@...zon.com>
To: <kprateek.nayak@....com>
CC: <mingo@...hat.com>, <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <bsegall@...gle.com>, <mgorman@...e.de>,
	<bristot@...hat.com>, <vschneid@...hat.com>, <dwmw@...zon.co.uk>,
	<jschoenh@...zon.de>, <liuyuxua@...zon.com>
Subject: [PATCH] sched: Optimize core cookie matching check

Early return true if the core cookie matches. This avoids the SMT mask
loop to check for an idle core, which might be more expensive on wide
platforms.

Signed-off-by: Fernand Sieber <sieberf@...zon.com>
---
 kernel/sched/sched.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index adfb6e3409d7..381cd561e99b 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1432,6 +1432,9 @@ static inline bool sched_core_cookie_match(struct rq *rq, struct task_struct *p)
 	if (!sched_core_enabled(rq))
 		return true;
 
+	if (rq->core->core_cookie == p->core_cookie)
+		return true;
+
 	for_each_cpu(cpu, cpu_smt_mask(cpu_of(rq))) {
 		if (!available_idle_cpu(cpu)) {
 			idle_core = false;
@@ -1443,7 +1446,7 @@ static inline bool sched_core_cookie_match(struct rq *rq, struct task_struct *p)
 	 * A CPU in an idle core is always the best choice for tasks with
 	 * cookies.
 	 */
-	return idle_core || rq->core->core_cookie == p->core_cookie;
+	return idle_core;
 }
 
 static inline bool sched_group_cookie_match(struct rq *rq,
-- 
2.43.0




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