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

[Aiqun(Maria) Yu]

On 6/15/2026 10:09 PM, Xin Zhao wrote:
> 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.

This format looks better.

> 
>> ---
>> 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)

Still have the doubt why need to do active load balance when the current
is not CFS. And busiest->curr->on_rq==0 case only.

Is it should be like:
if ((busiest->curr->sched_class == &fair_sched_class) ||
unlikely(!task_on_rq_queued(busiest->curr)));

if busiest->curr->on_rq==2 (TASK_ON_RQ_MIGRATING), it is no need to do
active_balance as well.

>> +				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
> 


-- 
Thx and BRs,
Aiqun(Maria) Yu