linux-kernel - Re: [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load

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Date:   Thu, 14 Apr 2022 17:29:28 +0800
From:   Kuyo Chang <kuyo.chang@...iatek.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        "Mel Gorman" <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>
CC:     <wsd_upstream@...iatek.com>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH 1/1] [PATCH v2]sched/pelt: Refine the enqueue_load_avg
 calculate method

On Thu, 2022-04-14 at 11:02 +0200, Dietmar Eggemann wrote:
> On 14/04/2022 03:59, Kuyo Chang wrote:
> > From: kuyo chang <kuyo.chang@...iatek.com>
> 
> [...]
> 
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index d4bd299d67ab..159274482c4e 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3829,10 +3829,12 @@ static void attach_entity_load_avg(struct
> > cfs_rq *cfs_rq, struct sched_entity *s
> >  
> >  	se->avg.runnable_sum = se->avg.runnable_avg * divider;
> >  
> > -	se->avg.load_sum = divider;
> > -	if (se_weight(se)) {
> > +	se->avg.load_sum = se->avg.load_avg * divider;
> > +	if (se_weight(se) < se->avg.load_sum) {
> >  		se->avg.load_sum =
> > -			div_u64(se->avg.load_avg * se->avg.load_sum,
> > se_weight(se));
> > +			div_u64(se->avg.load_sum, se_weight(se));
> 
> Seems that this will fit on one line now. No braces needed then.

Thanks for your friendly reminder.

> 
> > +	} else {
> > +		se->avg.load_sum = 1;
> >  	}
> >  
> >  	enqueue_load_avg(cfs_rq, se);
> 
> Looks like taskgroups are not affected since they get always online
> with cpu.shares/weight = 1024 (cgroup v1):
> 
> cpu_cgroup_css_online() -> online_fair_sched_group() ->
> attach_entity_cfs_rq() -> attach_entity_load_avg()
> 
> And reweight_entity() does not have this issue.
> 
> Tested with `qemu-system-x86_64 ... cores=64 ... -enable-kvm` and
> weight=88761 for nice=0 tasks plus forcing se->avg.load_avg = 1
> before
> the div_u64() in attach_entity_load_avg().
> 
> Tested-by: Dietmar Eggemann <dietmar.eggemann@....com>