linux-kernel - [PATCH] sched/fair: Return the busiest group only if imbalance is meaningful

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Message-Id: <1649244204-23471-1-git-send-email-zgpeng@tencent.com>
Date:   Wed,  6 Apr 2022 19:23:24 +0800
From:   zgpeng <zgpeng.linux@...il.com>
To:     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,
        bristot@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH] sched/fair: Return the busiest group only if imbalance is meaningful

When calculate_imbalance function calculate the imbalance, it may
actually get a negative number. In this case, it is meaningless to
return the so-called busiest group and continue to search for the
busiest cpu later. Therefore, only when the imbalance is greater
than 0 should return the busiest group, otherwise return NULL.

Signed-off-by: zgpeng <zgpeng@...cent.com>
Reviewed-by: Samuel Liao <samuelliao@...cent.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 601f8bd..9f75303 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9639,7 +9639,7 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
 force_balance:
 	/* Looks like there is an imbalance. Compute it */
 	calculate_imbalance(env, &sds);
-	return env->imbalance ? sds.busiest : NULL;
+	return env->imbalance > 0 ? sds.busiest : NULL;
 
 out_balanced:
 	env->imbalance = 0;
-- 
2.9.5