From 50ac1e131e2ab1d4e702a9d28fc196c1761c3174 Mon Sep 17 00:00:00 2001
From: Vincent Guittot <vincent.guittot@linaro.org>
Date: Mon, 21 Sep 2020 09:24:23 +0200
Subject: [PATCH] sched/fair: Minimize concurrent LBs between domain level
References: bnc#1155798 (CPU scheduler functional and performance backports)
Git-commit: e4d32e4d5444977d8dc25fa98b3ce0a65544db8c
Patch-mainline: v5.10-rc1
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 <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/20200921072424.14813-4-vincent.guittot@linaro.org
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
kernel/sched/fair.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d0496e8fb7d7..ce74584f8749 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9731,6 +9731,15 @@ 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;