From 892d59c22208be820a5463b5f74eb7f0b7f2b03a Mon Sep 17 00:00:00 2001 From: Valentin Schneider Date: Thu, 17 Jan 2019 15:34:08 +0000 Subject: sched/fair: Explain LLC nohz kick condition Provide a comment explaining the LLC related nohz kick in nohz_balancer_kick(). Signed-off-by: Valentin Schneider Signed-off-by: Peter Zijlstra (Intel) Cc: Dietmar.Eggemann@arm.com Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: morten.rasmussen@arm.com Cc: vincent.guittot@linaro.org Link: https://lkml.kernel.org/r/20190117153411.2390-3-valentin.schneider@arm.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0692c8ff6ff6..ac6b52d8c79e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9601,8 +9601,13 @@ static void nohz_balancer_kick(struct rq *rq) sds = rcu_dereference(per_cpu(sd_llc_shared, cpu)); if (sds) { /* - * XXX: write a coherent comment on why we do this. - * See also: http://lkml.kernel.org/r/20111202010832.602203411@sbsiddha-desk.sc.intel.com + * If there is an imbalance between LLC domains (IOW we could + * increase the overall cache use), we need some less-loaded LLC + * domain to pull some load. Likewise, we may need to spread + * load within the current LLC domain (e.g. packed SMT cores but + * other CPUs are idle). We can't really know from here how busy + * the others are - so just get a nohz balance going if it looks + * like this LLC domain has tasks we could move. */ nr_busy = atomic_read(&sds->nr_busy_cpus); if (nr_busy > 1) { -- cgit v1.2.1