linux-kernel - Re: [PATCH v2] sched/fair: Sync se's load_avg with cfs_rq in reweight

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Message-ID: <8f358bc7-e1ed-4631-bdc1-4134b8f84a34@bytedance.com>
Date: Tue, 30 Jul 2024 18:26:44 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] sched/fair: Sync se's load_avg with cfs_rq in
 reweight_task




-------- 转发的消息 --------
主题: Re: [PATCH v2] sched/fair: Sync se's load_avg with cfs_rq in 
reweight_task
日期: Mon, 29 Jul 2024 11:06:33 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
收件人: Qais Yousef <qyousef@...alina.io>, K Prateek Nayak 
<kprateek.nayak@....com>
抄送: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, 
vincent.guittot@...aro.org, dietmar.eggemann@....com, 
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, 
vschneid@...hat.com, chengming.zhou@...ux.dev

Hello Qais,

在 2024/7/29 04:14, Qais Yousef 写道:
> On 07/22/24 10:47, K Prateek Nayak wrote:
>> (+ Qais)
>>
>> Hello Chuyi,
>>
>> On 7/20/2024 10:42 AM, Chuyi Zhou wrote:
>>> In reweight_task(), there are two situations:
>>>
>>> 1. The task was on_rq, then the task's load_avg is accurate because we
>>> synchronized it with cfs_rq through update_load_avg() in dequeue_task().
>>>
>>> 2. The task is sleeping, its load_avg might not have been updated for some
>>> time, which can result in inaccurate dequeue_load_avg() in
>>> reweight_entity().
>>>
>>> This patch solves this by using update_load_avg() to synchronize the
>>> load_avg of se with cfs_rq. For tasks were on_rq, since we already update
>>> load_avg to accurate values in dequeue_task(), this change will not have
>>> other effects due to the short time interval between the two updates.
>>>
>>> Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
>>> ---
>>> Changes in v2:
>>> - change the description in commit log.
>>> - use update_load_avg() in reweight_task() rather than in reweight_entity
>>> suggested by chengming.
>>> - Link to v1: https://lore.kernel.org/lkml/20240716150840.23061-1-zhouchuyi@bytedance.com/
>>> ---
>>>    kernel/sched/fair.c | 3 +++
>>>    1 file changed, 3 insertions(+)
>>>
>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>> index 9057584ec06d..b1e07ce90284 100644
>>> --- a/kernel/sched/fair.c
>>> +++ b/kernel/sched/fair.c
>>> @@ -3835,12 +3835,15 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
>>>    	}
>>>    }
>>> +static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags);
>>> +
>>>    void reweight_task(struct task_struct *p, const struct load_weight *lw)
>>>    {
>>>    	struct sched_entity *se = &p->se;
>>>    	struct cfs_rq *cfs_rq = cfs_rq_of(se);
>>>    	struct load_weight *load = &se->load;
>>> +	update_load_avg(cfs_rq, se, 0);
> 
> White space and a comment perhaps?
> 
> LGTM anyway.

Thanks for taking a look, will send another patch later.

(V3 
link:https://lore.kernel.org/lkml/20240723114247.104848-1-zhouchuyi@bytedance.com/)