linux-kernel - Re: [RFC PATCH 3/4] sched/fair: delay update_tg_load_avg() for cfs

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Message-ID: <20230721064217.GA225030@ziqianlu-dell>
Date:   Fri, 21 Jul 2023 14:42:17 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
CC:     Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        "Steven Rostedt" <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        "Valentin Schneider" <vschneid@...hat.com>,
        Tim Chen <tim.c.chen@...el.com>,
        "Nitin Tekchandani" <nitin.tekchandani@...el.com>,
        Yu Chen <yu.c.chen@...el.com>,
        Waiman Long <longman@...hat.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3/4] sched/fair: delay update_tg_load_avg() for
 cfs_rq's removed load

On Thu, Jul 20, 2023 at 05:22:26PM +0200, Dietmar Eggemann wrote:
> On 20/07/2023 17:02, Vincent Guittot wrote:
> > On Thu, 20 Jul 2023 at 16:42, Aaron Lu <aaron.lu@...el.com> wrote:
> >>
> >> On Thu, Jul 20, 2023 at 03:10:30PM +0200, Vincent Guittot wrote:
> >>> On Wed, 19 Jul 2023 at 15:29, Aaron Lu <aaron.lu@...el.com> wrote:
> >>>>
> >>>> On Wed, Jul 19, 2023 at 11:47:06AM +0200, Vincent Guittot wrote:
> >>>>> On Wed, 19 Jul 2023 at 10:01, Aaron Lu <aaron.lu@...el.com> wrote:
> >>>>>>
> >>>>>> On Wed, Jul 19, 2023 at 01:18:26PM +0800, Aaron Lu wrote:
> 
> [...]
> 
> > What was wrong with your proposal to limit the update inside
> > update_tg_load_avg()  ? except maybe s/1000000/NSEC_PER_MSEC/ and
> > computing delta after testing the time since last update
> > 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a80a73909dc2..e48fd0e6982d 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3665,6 +3665,7 @@ static inline bool cfs_rq_is_decayed(struct
> > cfs_rq *cfs_rq)
> >  static inline void update_tg_load_avg(struct cfs_rq *cfs_rq)
> >  {
> >         long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;
> > +       u64 now = cfs_rq_clock_pelt(cfs_rq);
> 
> Could this be `u64 now = sched_clock_cpu()` like in
> migrate_se_pelt_lag() or newidle_balance() to avoid the time morphing
> due to PELT's frequency and uArch invariance?

Yes, will use sched_clock_cpu() instead of cfs_rq_clock_pelt().
Thanks.

> > 
> >         /*
> >          * No need to update load_avg for root_task_group as it is not used.
> 
> [...]
>