linux-kernel - Re: [PATCH] sched/fair: Sync se's load_avg with cfs_rq in reweight

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Message-ID: <cea46f88-6a4b-48c6-bbd7-033a3fc5d34d@bytedance.com>
Date: Thu, 18 Jul 2024 10:32:36 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: Chengming Zhou <chengming.zhou@...ux.dev>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Sync se's load_avg with cfs_rq in
 reweight_entity



在 2024/7/17 19:18, Chengming Zhou 写道:
> On 2024/7/16 23:08, Chuyi Zhou wrote:
>> In reweight_entity(), if !se->on_rq (e.g. when we are reweighting a
>> sleeping task), we should sync the load_avg of se to cfs_rq before 
>> calling
>> dequeue_load_avg(). Otherwise, the load_avg of this se can be inaccurate.
> 
> Good catch!
> 
>>
>> Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
>> ---
>>   kernel/sched/fair.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 9057584ec06d..2807f6e72ad1 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3782,6 +3782,8 @@ static void reweight_eevdf(struct sched_entity 
>> *se, u64 avruntime,
>>       se->deadline = avruntime + vslice;
>>   }
>> +static inline void update_load_avg(struct cfs_rq *cfs_rq, struct 
>> sched_entity *se, int flags);
>> +
>>   static void reweight_entity(struct cfs_rq *cfs_rq, struct 
>> sched_entity *se,
>>                   unsigned long weight)
>>   {
>> @@ -3795,7 +3797,11 @@ static void reweight_entity(struct cfs_rq 
>> *cfs_rq, struct sched_entity *se,
>>           if (!curr)
>>               __dequeue_entity(cfs_rq, se);
>>           update_load_sub(&cfs_rq->load, se->load.weight);
>> +    } else {
>> +        /* Sync with the cfs_rq before removing our load_avg */
>> +        update_load_avg(cfs_rq, se, 0);
> 
> I think it's suboptimal to update_load_avg() here unconditionally.
> 
> Because reweight_entity() has two types of usages:
> 
> 1. group se, which uses reweight_entity() in update_cfs_group(), which
> should already update_load_avg(), so should have no problem.
> 
> 2. task se, which uses reweight_entity() in reweight_task(), which 
> should be fixed for sleep task entity as you described above.
> 
> So IMHO, we should only update_load_avg() or sync_entity_load_avg() in
> reweight_task(), right?
> 

I will send another patch later.

Thanks for the review!