linux-kernel - [PATCH RESEND] sched: fair: drop useless cpumask_empty() in find_energy_efficient

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Message-ID: <20251207040543.407695-1-yury.norov@gmail.com>
Date: Sat,  6 Dec 2025 23:05:42 -0500
From: "Yury Norov (NVIDIA)" <yury.norov@...il.com>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Cc: "Yury Norov (NVIDIA)" <yury.norov@...il.com>,
	Markus Elfring <Markus.Elfring@....de>,
	Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
	K Prateek Nayak <kprateek.nayak@....com>
Subject: [PATCH RESEND] sched: fair: drop useless cpumask_empty() in find_energy_efficient_cpu()

cpumask_empty() call is O(N) and useless because the previous
cpumask_and() returns false for empty 'cpus'. Drop it.

CC: Markus Elfring <Markus.Elfring@....de>
Reviewed-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Reviewed-by: K Prateek Nayak <kprateek.nayak@....com>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
---
Rebased and re-tested on top of master. Original patch:
https://lore.kernel.org/all/20250911023426.457745-1-yury.norov@gmail.com/

 kernel/sched/fair.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e04f94233cda..af9e9dbdaa6d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8362,9 +8362,7 @@ static int find_energy_efficient_cpu(struct task_struct *p, int prev_cpu)
 		int max_spare_cap_cpu = -1;
 		int fits, max_fits = -1;
 
-		cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask);
-
-		if (cpumask_empty(cpus))
+		if (!cpumask_and(cpus, perf_domain_span(pd), cpu_online_mask))
 			continue;
 
 		/* Account external pressure for the energy estimation */
-- 
2.43.0