linux-kernel - [PATCH 3/4] sched/fair: Check for blocked task after time check

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Message-ID: <20251201183146.74443-4-sshegde@linux.ibm.com>
Date: Tue,  2 Dec 2025 00:01:45 +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 3/4] sched/fair: Check for blocked task after time check

nohz.has_blocked can be updated often as and when CPUs enter idle state.
But stats are updated only at regular intervals. Usually fixed to
LOAD_AVG_PERIOD=32. 

Read the value only after time check is successful to avoid cache
references to it.

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 55746274af06..5534822fd754 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12440,8 +12440,8 @@ static void nohz_balancer_kick(struct rq *rq)
 	 */
 	nohz_balance_exit_idle(rq);
 
-	if (READ_ONCE(nohz.has_blocked) &&
-	    time_after(now, READ_ONCE(nohz.next_blocked)))
+	if (time_after(now, READ_ONCE(nohz.next_blocked)) &&
+	    READ_ONCE(nohz.has_blocked))
 		flags = NOHZ_STATS_KICK;
 
 	if (time_before(now, nohz.next_balance))
-- 
2.43.0