linux-kernel - [PATCH 4/4 v2] sched/fair: reduce busy load balance interval

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Message-Id: <20200921072424.14813-5-vincent.guittot@linaro.org>
Date:   Mon, 21 Sep 2020 09:24:24 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     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:     valentin.schneider@....com, pauld@...hat.com, hdanton@...a.com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 4/4 v2] sched/fair: reduce busy load balance interval

The busy_factor, which increases load balance interval when a cpu is busy,
is set to 32 by default. This value generates some huge LB interval on
large system like the THX2 made of 2 node x 28 cores x 4 threads.
For such system, the interval increases from 112ms to 3584ms at MC level.
And from 228ms to 7168ms at NUMA level.

Even on smaller system, a lower busy factor has shown improvement on the
fair distribution of the running time so let reduce it for all.

Reviewed-by: Phil Auld <pauld@...hat.com>
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/topology.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 41df62884cea..a3a2417fec54 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1348,7 +1348,7 @@ sd_init(struct sched_domain_topology_level *tl,
 	*sd = (struct sched_domain){
 		.min_interval		= sd_weight,
 		.max_interval		= 2*sd_weight,
-		.busy_factor		= 32,
+		.busy_factor		= 16,
 		.imbalance_pct		= 117,
 
 		.cache_nice_tries	= 0,
-- 
2.17.1