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

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,