linux-kernel - [PATCH] sched/fair: Don't pull task if local group is more loaded than busiest group

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Date:   Wed, 25 Mar 2020 20:46:28 +0800
From:   Aubrey Li <aubrey.li@...el.com>
To:     vincent.guittot@...aro.org, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org
Cc:     tim.c.chen@...ux.intel.com, vpillai@...italocean.com,
        joel@...lfernandes.org, Aubrey Li <aubrey.li@...el.com>,
        Aubrey Li <aubrey.li@...ux.intel.com>
Subject: [PATCH] sched/fair: Don't pull task if local group is more loaded than busiest group

A huge number of load imbalance was observed when the local group
type is group_fully_busy, and the average load of local group is
greater than the selected busiest group, so the imbalance calculation
returns a negative value actually. Fix this problem by comparing the
average load before local group type check.

Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
---
 kernel/sched/fair.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c1217bf..c524369 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8862,17 +8862,17 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
 		goto out_balanced;
 
 	/*
+	 * If the local group is more loaded than the selected
+	 * busiest group don't try to pull any tasks.
+	 */
+	if (local->avg_load >= busiest->avg_load)
+		goto out_balanced;
+
+	/*
 	 * When groups are overloaded, use the avg_load to ensure fairness
 	 * between tasks.
 	 */
 	if (local->group_type == group_overloaded) {
-		/*
-		 * If the local group is more loaded than the selected
-		 * busiest group don't try to pull any tasks.
-		 */
-		if (local->avg_load >= busiest->avg_load)
-			goto out_balanced;
-
 		/* XXX broken for overlapping NUMA groups */
 		sds.avg_load = (sds.total_load * SCHED_CAPACITY_SCALE) /
 				sds.total_capacity;
-- 
2.7.4