linux-kernel - [PATCH 18/22] sched/core: remove unneeded cpumask_weight() in sched_core_cpu

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Date:   Tue, 10 May 2022 08:47:46 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Laight <David.Laight@...LAB.COM>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joe Perches <joe@...ches.com>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Nicholas Piggin <npiggin@...il.com>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Peter Zijlstra <peterz@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>, Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 18/22] sched/core: remove unneeded cpumask_weight() in sched_core_cpu_{starting,deactivate}

The following cpumask_any_but() implicitly calculates if number of smt cpus
is equal to 1, therefore we can drop the code that does it explicitly.

CC: Ben Segall <bsegall@...gle.com>
CC: Daniel Bristot de Oliveira <bristot@...hat.com>
CC: Dietmar Eggemann <dietmar.eggemann@....com>
CC: Ingo Molnar <mingo@...hat.com>
CC: Juri Lelli <juri.lelli@...hat.com>
CC: Mel Gorman <mgorman@...e.de>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Valentin Schneider <vschneid@...hat.com>
CC: Vincent Guittot <vincent.guittot@...aro.org>
CC: linux-kernel@...r.kernel.org
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
This is RFC because it drops WARN_ON_ONCE(rq->core != rq). If this warinig
is important, I'll rework the patch.

 kernel/sched/core.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9700001948d0..07b8f35cbe36 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6133,12 +6133,10 @@ static void sched_core_cpu_starting(unsigned int cpu)
 
 	WARN_ON_ONCE(rq->core != rq);
 
-	/* if we're the first, we'll be our own leader */
-	if (cpumask_weight(smt_mask) == 1)
-		goto unlock;
-
 	/* find the leader */
 	t = cpumask_any_but(smt_mask, cpu);
+
+	/* if we're the first, we'll be our own leader */
 	if (t >= nr_cpu_ids)
 		goto unlock;
 
@@ -6171,18 +6169,14 @@ static void sched_core_cpu_deactivate(unsigned int cpu)
 
 	sched_core_lock(cpu, &flags);
 
-	/* if we're the last man standing, nothing to do */
-	if (cpumask_weight(smt_mask) == 1) {
-		WARN_ON_ONCE(rq->core != rq);
-		goto unlock;
-	}
-
 	/* if we're not the leader, nothing to do */
 	if (rq->core != rq)
 		goto unlock;
 
 	/* find a new leader */
 	t = cpumask_any_but(smt_mask, cpu);
+
+	/* if we're the last man standing, nothing to do */
 	if (t >= nr_cpu_ids)
 		goto unlock;
 
-- 
2.32.0