From 387bc8b5536eeb0a92f4b4ab553539eaea2ac0ba Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Mon, 19 Jun 2017 04:12:02 +0200 Subject: [PATCH] sched/fair: Spare idle load balancing on nohz_full CPUs Although idle load balancing obviously only concerns idle CPUs, it can be a disturbance on a busy nohz_full CPU. Indeed a CPU can only get rid of an idle load balancing duty once a tick fires while it runs a task and this can take a while on a nohz_full CPU. We could fix that and escape the idle load balancing duty from the very idle exit path but that would bring unecessary overhead. Lets just not bother and leave that job to housekeeping CPUs (those outside nohz_full range). The nohz_full CPUs simply don't want any disturbance. Signed-off-by: Frederic Weisbecker Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1497838322-10913-4-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a24661ac3d23..694c258b8771 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -8683,6 +8683,10 @@ void nohz_balance_enter_idle(int cpu) if (!cpu_active(cpu)) return; + /* Spare idle load balancing on CPUs that don't want to be disturbed: */ + if (!is_housekeeping_cpu(cpu)) + return; + if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu))) return;