linux-kernel - [PATCH] sched_ext: Simplify cpumask computation in balance

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Message-ID: <20250307064533.2663-1-lirongqing@baidu.com>
Date: Fri, 7 Mar 2025 14:45:33 +0800
From: lirongqing <lirongqing@...du.com>
To: <tj@...nel.org>, <void@...ifault.com>, <arighi@...dia.com>,
	<changwoo@...lia.com>, <mingo@...hat.com>, <peterz@...radead.org>,
	<juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
	<dietmar.eggemann@....com>, <rostedt@...dmis.org>, <bsegall@...gle.com>,
	<mgorman@...e.de>, <vschneid@...hat.com>, <linux-kernel@...r.kernel.org>
CC: Li RongQing <lirongqing@...du.com>
Subject: [PATCH] sched_ext: Simplify cpumask computation in balance_scx

From: Li RongQing <lirongqing@...du.com>

Compare SMT CPU against RQ CPU and skip balance it, to avoid calling
for_each_cpu_andnot() and cpumask_of(), they are relatively expensive

Signed-off-by: Li RongQing <lirongqing@...du.com>
---
 kernel/sched/ext.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 0f1da19..7e40ede 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2920,11 +2920,19 @@ static int balance_scx(struct rq *rq, struct task_struct *prev,
 	 */
 	if (sched_core_enabled(rq)) {
 		const struct cpumask *smt_mask = cpu_smt_mask(cpu_of(rq));
-		int scpu;
+		int scpu, cpu;
 
-		for_each_cpu_andnot(scpu, smt_mask, cpumask_of(cpu_of(rq))) {
-			struct rq *srq = cpu_rq(scpu);
-			struct task_struct *sprev = srq->curr;
+		cpu = cpu_of(rq);
+
+		for_each_cpu(scpu, smt_mask) {
+			struct rq *srq;
+			struct task_struct *sprev;
+
+			if (scpu == cpu)
+				continue;
+
+			srq = cpu_rq(scpu);
+			sprev = srq->curr;
 
 			WARN_ON_ONCE(__rq_lockp(rq) != __rq_lockp(srq));
 			update_rq_clock(srq);
-- 
2.9.4