linux-kernel - [PATCH 1/4] sched/fair: Move checking for nohz cpus after time check

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Message-ID: <20251201183146.74443-2-sshegde@linux.ibm.com>
Date: Tue,  2 Dec 2025 00:01:43 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, kprateek.nayak@....com
Cc: sshegde@...ux.ibm.com, dietmar.eggemann@....com, vschneid@...hat.com,
        rostedt@...dmis.org, tglx@...utronix.de, tim.c.chen@...ux.intel.com
Subject: [PATCH 1/4] sched/fair: Move checking for nohz cpus after time check

Idle load balancer is kicked off only after time check. So move
the atomic read after the time check.

If there are no nohz CPUs there likely has_blocked should be reset
too. So stats load balancing shouldn't much difference. 

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com> 
---
 kernel/sched/fair.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 769d7b7990df..61cc3fdfa45b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12440,19 +12440,18 @@ static void nohz_balancer_kick(struct rq *rq)
 	 */
 	nohz_balance_exit_idle(rq);
 
-	/*
-	 * None are in tickless mode and hence no need for NOHZ idle load
-	 * balancing:
-	 */
-	if (likely(!atomic_read(&nohz.nr_cpus)))
-		return;
-
 	if (READ_ONCE(nohz.has_blocked) &&
 	    time_after(now, READ_ONCE(nohz.next_blocked)))
 		flags = NOHZ_STATS_KICK;
 
 	if (time_before(now, nohz.next_balance))
 		goto out;
+	/*
+	 * None are in tickless mode and hence no need for NOHZ idle load
+	 * balancing:
+	 */
+	if (likely(!atomic_read(&nohz.nr_cpus)))
+		return;
 
 	if (rq->nr_running >= 2) {
 		flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
-- 
2.43.0