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

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Message-ID: <20240728201427.kxzn53vurpf7ij3i@airbuntu>
Date: Sun, 28 Jul 2024 21:14:27 +0100
From: Qais Yousef <qyousef@...alina.io>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Chuyi Zhou <zhouchuyi@...edance.com>, 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,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/fair: Sync se's load_avg with cfs_rq in
 reweight_task

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.