Re: [PATCH v3 1/2] sched/fair: Don't trigger active lb if src_rq->curr is CFS and not on_rq

[Xin Zhao]

On Mon, 15 Jun 2026 15:39:22 +0200 Valentin Schneider <vschneid@xxxxxxxxxx> wrote:

> > @@ -13436,7 +13436,9 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
> >                        * ->active_balance_work.  Once set, it's cleared
> >                        * only after active load balance is finished.
> >                        */
> > -			if (!busiest->active_balance) {
> > +			if (!busiest->active_balance &&
> > +			    !(busiest->curr->sched_class == &fair_sched_class &&
> > +			      !busiest->curr->on_rq)) {
> 
> This should be commented; I restructured this a little, it's one more label
> but it reads better to me, what do you think?

:) Thank you for your changes; it looks much better now, and the necessary
comments have been added.

> ---
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index d78467ec6ee13..a0ac31a3be988 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -13482,12 +13482,22 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
>  			 * ->active_balance_work.  Once set, it's cleared
>  			 * only after active load balance is finished.
>  			 */
> -			if (!busiest->active_balance) {
> -				busiest->active_balance = 1;
> -				busiest->push_cpu = this_cpu;
> -				active_balance = 1;
> -			}
> +			if (busiest->active_balance)
> +				goto no_active_balance;
>  
> +			/*
> +			 * @busiest dropped its rq_lock in the middle of
> +			 * scheduling out its ->curr task (->on_rq := 0), no
> +			 * need to forcefully punt it away with active balance.
> +			 */
> +			if ((busiest->curr->sched_class == &fair_sched_class) &&
> +			    !busiest->curr->on_rq)
> +				goto no_active_balance;
> +
> +			busiest->active_balance = 1;
> +			busiest->push_cpu = this_cpu;
> +			active_balance = 1;
> +no_active_balance:
>  			preempt_disable();
>  			raw_spin_rq_unlock_irqrestore(busiest, flags);
>  			if (active_balance) {

Thanks
Xin Zhao