linux-kernel - [tip: sched/urgent] sched: Teach the forced-newidle balancer about CPU affinity limitation.

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Date:   Tue, 05 Apr 2022 08:22:01 -0000
From:   "tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched: Teach the forced-newidle balancer about
 CPU affinity limitation.

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     386ef214c3c6ab111d05e1790e79475363abaa05
Gitweb:        https://git.kernel.org/tip/386ef214c3c6ab111d05e1790e79475363abaa05
Author:        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate:    Thu, 17 Mar 2022 15:51:32 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 05 Apr 2022 09:59:36 +02:00

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

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@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/YjNK9El+3fzGmswf@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 017ee78..51efaab 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6006,7 +6006,7 @@ 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)