[PATCH] sched: keep quiescent cpu out of idle balance loop

[Lei Wen]

Cpu which is put into quiescent mode, would remove itself
from kernel's sched_domain, and want others not disturb its
task running. But current scheduler would not checking whether
that cpu is setting in such mode, and still insist the quiescent
cpu to response the nohz load balance.

Fix it by preventing such cpu set nohz.idle_cpus_mask in the
first place.

Signed-off-by: Lei Wen <leiwen@xxxxxxxxxxx>
---
 kernel/sched/fair.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 235cfa7..bc85022 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6883,6 +6883,13 @@ void nohz_balance_enter_idle(int cpu)
 	if (!cpu_active(cpu))
 		return;
 
+	/*
+	 * If this cpu is kept outside of root domain, we don't bother
+	 * to ask it for nohz balance.
+	 */
+	if (!cpumask_test_cpu(cpu, this_rq()->rd.span))
+		return;
+
 	if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
 		return;
 
-- 
1.8.3.2

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