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@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/20200921072424.14813-5-vincent.guittot@linaro.org

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 41df628..a3a2417 100644 (file)
--- 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,