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* [PATCH] sched/fair: Fix per-CPU kthread and wakee stacking for asym CPU capacity
@ 2021-11-24 14:14 Vincent Donnefort
  2021-11-24 17:11 ` Valentin Schneider
  2021-11-25  9:10 ` Vincent Guittot
  0 siblings, 2 replies; 5+ messages in thread
From: Vincent Donnefort @ 2021-11-24 14:14 UTC (permalink / raw)
  To: peterz, mingo, vincent.guittot
  Cc: linux-kernel, mgorman, dietmar.eggemann, valentin.schneider,
	Vincent Donnefort

A shortcut has been introduced in select_idle_sibling() to return prev_cpu
if the wakee is woken up by a per-CPU kthread. This is an issue for
asymmetric CPU capacity systems where the wakee might not fit prev_cpu
anymore. Evaluate asym_fits_capacity() for prev_cpu before using that
shortcut.

Fixes: 52262ee567ad ("sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression")
Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6291876a9d32..b90dc6fd86ca 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6410,7 +6410,8 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
 	 */
 	if (is_per_cpu_kthread(current) &&
 	    prev == smp_processor_id() &&
-	    this_rq()->nr_running <= 1) {
+	    this_rq()->nr_running <= 1 &&
+	    asym_fits_capacity(task_util, prev)) {
 		return prev;
 	}
 
-- 
2.25.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2021-11-25  9:18 UTC | newest]

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2021-11-24 14:14 [PATCH] sched/fair: Fix per-CPU kthread and wakee stacking for asym CPU capacity Vincent Donnefort
2021-11-24 17:11 ` Valentin Schneider
2021-11-24 17:58   ` Vincent Donnefort
2021-11-24 18:04     ` Valentin Schneider
2021-11-25  9:10 ` Vincent Guittot

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