linux-kernel - [PATCH v2 1/4] sched/fair: Use READ_ONCE() to read sg->asym_prefer

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Message-ID: <20250409053446.23367-2-kprateek.nayak@amd.com>
Date: Wed, 9 Apr 2025 05:34:43 +0000
From: K Prateek Nayak <kprateek.nayak@....com>
To: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
	<vincent.guittot@...aro.org>, "Gautham R. Shenoy" <gautham.shenoy@....com>,
	Mario Limonciello <mario.limonciello@....com>, "Rafael J. Wysocki"
	<rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt
	<rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman
	<mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, Waiman Long
	<llong@...hat.com>, Swapnil Sapkal <swapnil.sapkal@....com>, "Dhananjay
 Ugwekar" <Dhananjay.Ugwekar@....com>, Huang Rui <ray.huang@....com>, "Perry
 Yuan" <perry.yuan@....com>, K Prateek Nayak <kprateek.nayak@....com>
Subject: [PATCH v2 1/4] sched/fair: Use READ_ONCE() to read sg->asym_prefer_cpu

Subsequent commits add the support to dynamically update the sched_group
struct's "asym_prefer_cpu" member from a remote CPU. Use READ_ONCE()
when reading the "sg->asym_prefer_cpu" to ensure load balancer always
reads the latest value.

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
 kernel/sched/fair.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0c19459c8042..5e1bd9e8464c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10251,7 +10251,7 @@ sched_group_asym(struct lb_env *env, struct sg_lb_stats *sgs, struct sched_group
 	    (sgs->group_weight - sgs->idle_cpus != 1))
 		return false;
 
-	return sched_asym(env->sd, env->dst_cpu, group->asym_prefer_cpu);
+	return sched_asym(env->sd, env->dst_cpu, READ_ONCE(group->asym_prefer_cpu));
 }
 
 /* One group has more than one SMT CPU while the other group does not */
@@ -10488,7 +10488,8 @@ static bool update_sd_pick_busiest(struct lb_env *env,
 
 	case group_asym_packing:
 		/* Prefer to move from lowest priority CPU's work */
-		return sched_asym_prefer(sds->busiest->asym_prefer_cpu, sg->asym_prefer_cpu);
+		return sched_asym_prefer(READ_ONCE(sds->busiest->asym_prefer_cpu),
+					 READ_ONCE(sg->asym_prefer_cpu));
 
 	case group_misfit_task:
 		/*
-- 
2.34.1