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

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Message-ID: <2acd7c1d-e2b4-40a0-85de-55f9b2635dad@linux.ibm.com>
Date: Wed, 12 Nov 2025 20:07:24 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.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>
Subject: Re: [PATCH 2/4] sched/fair: Small cleanup to sched_balance_newidle()



On 11/7/25 9:36 PM, 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();
>   	sd = rcu_dereference_check_sched_domain(this_rq->sd);
> +	if (!sd) {
> +		rcu_read_unlock();
> +		goto out;
> +	}
>   

when is sd null? on isol_cpus ?

if sd is null, i think we are skipping these compared to earlier.

         t0 = sched_clock_cpu(this_cpu);
         sched_balance_update_blocked_averages(this_cpu);

>   	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();
> 
>