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

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Message-ID: <1456057a-6289-491a-a776-84856226d97b@amd.com>
Date: Thu, 11 Sep 2025 12:14:57 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Yury Norov <yury.norov@...il.com>, Ingo Molnar <mingo@...hat.com>, "Peter
 Zijlstra" <peterz@...radead.org>, 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>
Subject: Re: [PATCH] sched: fair: drop useless cpumask_empty() in
 find_energy_efficient_cpu()

Hello Yury,

On 9/11/2025 8:04 AM, Yury Norov wrote:
> From: Yury Norov (NVIDIA) <yury.norov@...il.com>
> 
> cpumask_empty() call is O(N) and useless, because the previous
> cpumask_and() returns false for empty 'cpus'.

I agree. Please feel free to include:

Reviewed-by: K Prateek Nayak <kprateek.nayak@....com>

> 
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.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 b173a059315c..7229339cbb1b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8320,9 +8320,7 @@ 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 */

-- 
Thanks and Regards,
Prateek