linux-kernel - Re: [PATCH 2/4] sched/fair: Small cleanup to sched_balance

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Message-ID: <bcd48c73-b65f-47be-917b-7fb2b8ed8ec0@arm.com>
Date: Mon, 10 Nov 2025 14:55:34 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Peter Zijlstra <peterz@...radead.org>, Chris Mason <clm@...a.com>,
 Joseph Salisbury <joseph.salisbury@...cle.com>,
 Adam Li <adamli@...amperecomputing.com>,
 Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>, Josh Don <joshdon@...gle.com>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] sched/fair: Small cleanup to sched_balance_newidle()

On 07.11.25 17:06, Peter Zijlstra wrote:
> Pull out the !sd check to simplify code.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/fair.c |   10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -12811,14 +12811,16 @@ static int sched_balance_newidle(struct
>  
>  	rcu_read_lock();

Maybe scoped_guard(rcu) here?

>  	sd = rcu_dereference_check_sched_domain(this_rq->sd);
> +	if (!sd) {
> +		rcu_read_unlock();
> +		goto out;
> +	}
>  
>  	if (!get_rd_overloaded(this_rq->rd) ||
> -	    (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
> +	    this_rq->avg_idle < sd->max_newidle_lb_cost) {
>  
> -		if (sd)
> -			update_next_balance(sd, &next_balance);
> +		update_next_balance(sd, &next_balance);
>  		rcu_read_unlock();
> -
>  		goto out;
>  	}
>  	rcu_read_unlock();