linux-kernel - [PATCH] sched_ext: idle: small CPU iteration refactoring

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Message-ID: <20250104090009.331193-1-arighi@nvidia.com>
Date: Sat,  4 Jan 2025 10:00:09 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>
Cc: Yury Norov <yury.norov@...il.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] sched_ext: idle: small CPU iteration refactoring

Replace the loop to check if all SMT CPUs are idle with
cpumask_subset(). This simplifies the code and slightly improves
efficiency, while preserving the original behavior.

Note that idle_masks.smt handling remains racy, which is acceptable as
it serves as an optimization and is self-correcting.

Suggested-by: Yury Norov <yury.norov@...il.com>
Signed-off-by: Andrea Righi <arighi@...dia.com>
---
 kernel/sched/ext.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 926579624c41..0ce116e0f67c 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3671,10 +3671,8 @@ void __scx_update_idle(struct rq *rq, bool idle)
 			 * idle_masks.smt handling is racy but that's fine as
 			 * it's only for optimization and self-correcting.
 			 */
-			for_each_cpu(cpu, smt) {
-				if (!cpumask_test_cpu(cpu, idle_masks.cpu))
-					return;
-			}
+			if (!cpumask_subset(smt, idle_masks.cpu))
+				return;
 			cpumask_or(idle_masks.smt, idle_masks.smt, smt);
 		} else {
 			cpumask_andnot(idle_masks.smt, idle_masks.smt, smt);
-- 
2.47.1