[PATCH] sched: Teach the forced-newidle balancer about CPU affinity limitation.

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: [PATCH] sched: Teach the forced-newidle balancer about CPU affinity limitation.
Date: Thu, 17 Mar 2022 15:51:32 +0100	[thread overview]
Message-ID: <YjNK9El+3fzGmswf@linutronix.de> (raw)
In-Reply-To: <YjMk4b3vbR4vJqfO@linutronix.de>

try_steal_cookie() looks at task_struct::cpus_mask to decide if the
task could be moved to `this' CPU. It ignores that the task might be in
a migration disabled section while not on the CPU. In this case the task
must not be moved otherwise per-CPU assumption are broken.

Use is_cpu_allowed(), as suggested by Peter Zijlstra, to decide if the a
task can be moved.

Fixes: d2dfa17bc7de6 ("sched: Trivial forced-newidle balancer")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a44414946de3d..421ace2e007de 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5923,7 +5923,7 @@ static bool try_steal_cookie(int this, int that)
 		if (p == src->core_pick || p == src->curr)
 			goto next;
 
-		if (!cpumask_test_cpu(this, &p->cpus_mask))
+		if (!is_cpu_allowed(p, this))
 			goto next;
 
 		if (p->core_occupation > dst->idle->core_occupation)
-- 
2.35.1

