From: Vincent Guittot Date: Mon, 21 Sep 2020 07:24:23 +0000 (+0200) Subject: sched/fair: Minimize concurrent LBs between domain level X-Git-Tag: v5.10-rc1~203^2~8 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e4d32e4d5444977d8dc25fa98b3ce0a65544db8c;p=thirdparty%2Fkernel%2Flinux.git sched/fair: Minimize concurrent LBs between domain level sched domains tend to trigger simultaneously the load balance loop but the larger domains often need more time to collect statistics. This slowness makes the larger domain trying to detach tasks from a rq whereas tasks already migrated somewhere else at a sub-domain level. This is not a real problem for idle LB because the period of smaller domains will increase with its CPUs being busy and this will let time for higher ones to pulled tasks. But this becomes a problem when all CPUs are already busy because all domains stay synced when they trigger their LB. A simple way to minimize simultaneous LB of all domains is to decrement the the busy interval by 1 jiffies. Because of the busy_factor, the interval of larger domain will not be a multiple of smaller ones anymore. Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Phil Auld Link: https://lkml.kernel.org/r/20200921072424.14813-4-vincent.guittot@linaro.org --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 5e3add351b895..24a5ee63718fa 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9790,6 +9790,15 @@ get_sd_balance_interval(struct sched_domain *sd, int cpu_busy) /* scale ms to jiffies */ interval = msecs_to_jiffies(interval); + + /* + * Reduce likelihood of busy balancing at higher domains racing with + * balancing at lower domains by preventing their balancing periods + * from being multiples of each other. + */ + if (cpu_busy) + interval -= 1; + interval = clamp(interval, 1UL, max_load_balance_interval); return interval;