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From: Vincent Donnefort <vincent.donnefort@arm.com>
To: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org
Cc: linux-kernel@vger.kernel.org, mgorman@techsingularity.net,
	dietmar.eggemann@arm.com, valentin.schneider@arm.com,
	Vincent Donnefort <vincent.donnefort@arm.com>
Subject: [PATCH] sched/fair: Fix per-CPU kthread and wakee stacking for asym CPU capacity
Date: Wed, 24 Nov 2021 14:14:35 +0000	[thread overview]
Message-ID: <20211124141435.3125147-1-vincent.donnefort@arm.com> (raw)

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


             reply	other threads:[~2021-11-24 14:18 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-24 14:14 Vincent Donnefort [this message]
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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