Re: [PATCH 1/4] sched/eevdf: Fix vruntime adjustment on reweight

[Abel Wu <wuyun.abel@bytedance.com>]

On 11/16/23 12:48 PM, Abel Wu Wrote:
> On 11/15/23 11:36 PM, Yiwei Lin Wrote:
>>
>>> @@ -3712,8 +3811,17 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>>>       enqueue_load_avg(cfs_rq, se);
>>>       if (se->on_rq) {
>>>           update_load_add(&cfs_rq->load, se->load.weight);
>>> -        if (cfs_rq->curr != se)
>>> -            avg_vruntime_add(cfs_rq, se);
>>> +        if (!curr) {
>>> +            /*
>>> +             * The entity's vruntime has been adjusted, so let's check
>>> +             * whether the rq-wide min_vruntime needs updated too. Since
>>> +             * the calculations above require stable min_vruntime rather
>>> +             * than up-to-date one, we do the update at the end of the
>>> +             * reweight process.
>>> +             */
>>> +            __enqueue_entity(cfs_rq, se);
>>> +            update_min_vruntime(cfs_rq);
>>> +        }
>>>       }
>>>   }
>> Sorry if I am asking stupid question...... It looks like reweight_entity() may have chance to change the weight of cfs_rq->curr entity, but we'll never update_min_vruntime() when reweighting it. Is there any reason that we can skip the update_min_vruntime() for this case?
> 
> No, you are right!

I was intended to update_min_vruntime() if se->on_rq and no matter
it is curr or not, just as you suggested. But after a second thought
I wonder if it is necessary to update *NOW*, since we will always
update_curr() before making any change to cfs_rq. Thoughts?