linux-kernel - [PATCH 2/4] sched/fair: Change likelyhood of nohz nr

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Message-ID: <20251201183146.74443-3-sshegde@linux.ibm.com>
Date: Tue,  2 Dec 2025 00:01:44 +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 2/4] sched/fair: Change likelyhood of nohz nr_cpus check

These days most of the system have multi cores. The likelyhood of
at least one or more CPUs in nohz (idle state) is higher.
So move likely to unlikely.

Allow stats balancing to complete when there are no nr_cpus as the check
happens later. Current code might race and may not set
nohz.has_blocked = 0 even when nohz.nr_cpus == 0

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 kernel/sched/fair.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 61cc3fdfa45b..55746274af06 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12448,10 +12448,10 @@ static void nohz_balancer_kick(struct rq *rq)
 		goto out;
 	/*
 	 * None are in tickless mode and hence no need for NOHZ idle load
-	 * balancing:
+	 * balancing, do stats update if its due
 	 */
-	if (likely(!atomic_read(&nohz.nr_cpus)))
-		return;
+	if (unlikely(!atomic_read(&nohz.nr_cpus)))
+		goto out;
 
 	if (rq->nr_running >= 2) {
 		flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
-- 
2.43.0