[tip: sched/core] sched/fair: Reduce busy load balance interval

[tip-bot2 for Vincent Guittot]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     6e7499135db724539ca887b3aa64122502875c71
Gitweb:        https://git.kernel.org/tip/6e7499135db724539ca887b3aa64122502875c71
Author:        Vincent Guittot <vincent.guittot@xxxxxxxxxx>
AuthorDate:    Mon, 21 Sep 2020 09:24:24 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Fri, 25 Sep 2020 14:23:26 +02:00

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.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Phil Auld <pauld@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200921072424.14813-5-vincent.guittot@xxxxxxxxxx
---
 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 41df628..a3a2417 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,