linux-kernel - Re: [PATCH 2/2] sched/deadline: Use cpumask_weight_and in dl_bw

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Message-ID: <20251110141141.GZ3245006@noisy.programming.kicks-ass.net>
Date: Mon, 10 Nov 2025 15:11:41 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: juri.lelli@...hat.com, mingo@...hat.com, vincent.guittot@...aro.org,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	dietmar.eggemann@....com, nico@...xnic.net
Subject: Re: [PATCH 2/2] sched/deadline: Use cpumask_weight_and in dl_bw_cpus

On Tue, Oct 14, 2025 at 03:33:42PM +0530, Shrikanth Hegde wrote:
> - cpumask_subset(a,b) -> cpumask_weight(a) should be same as 
> cpumask_weight_and(a,b)
> 
> - for_each_cpu_and(a,b) to count cpus could be replaced by
> cpumask_weight_and(a,b)
> 
> No Functional Change. It could save a few cycles since cpumask_weight_and 
> would be more efficient. Plus one less stack variable. 
> 
> Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
> ---
>  kernel/sched/deadline.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 8b7c4ee41fd8..a18f64b2e47c 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -125,20 +125,11 @@ static inline struct dl_bw *dl_bw_of(int i)
>  static inline int dl_bw_cpus(int i)
>  {
>  	struct root_domain *rd = cpu_rq(i)->rd;
> -	int cpus;
>  
>  	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
>  			 "sched RCU must be held");
>  
> -	if (cpumask_subset(rd->span, cpu_active_mask))
> -		return cpumask_weight(rd->span);
> -
> -	cpus = 0;
> -
> -	for_each_cpu_and(i, rd->span, cpu_active_mask)
> -		cpus++;
> -
> -	return cpus;
> +	return cpumask_weight_and(rd->span, cpu_active_mask);
>  }

Right, let me stick that on top of the change I have in queue/sched/core