linux-kernel - [PATCH] sched/fair: Use try_cmpxchg in task_numa

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Date:   Mon, 22 Aug 2022 19:39:56 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Uros Bizjak <ubizjak@...il.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH] sched/fair: Use try_cmpxchg in task_numa_work

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old
in task_numa_work. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

No functional change intended.

Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Uros Bizjak <ubizjak@...il.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 914096c5b1ae..efe73ee89989 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2802,7 +2802,7 @@ static void task_numa_work(struct callback_head *work)
 	}
 
 	next_scan = now + msecs_to_jiffies(p->numa_scan_period);
-	if (cmpxchg(&mm->numa_next_scan, migrate, next_scan) != migrate)
+	if (!try_cmpxchg(&mm->numa_next_scan, &migrate, next_scan))
 		return;
 
 	/*
-- 
2.37.1