linux-kernel - Re: [PATCH v5 4/4] sched/fair: update util_est only on util

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Message-ID: <20180308103703.GG2211@e110439-lin>
Date:   Thu, 8 Mar 2018 10:37:03 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>
Subject: Re: [PATCH v5 4/4] sched/fair: update util_est only on util_avg
 updates

On 08-Mar 10:48, Peter Zijlstra wrote:
> On Thu, Feb 22, 2018 at 05:01:53PM +0000, Patrick Bellasi wrote:
> > +#define UTIL_EST_NEED_UPDATE_FLAG 0x1
> 
> > @@ -5321,12 +5345,19 @@ static inline void util_est_dequeue(struct cfs_rq *cfs_rq,
> >  	if (!task_sleep)
> >  		return;
> >  
> > +	/*
> > +	 * Skip update of task's estimated utilization if the PELT signal has
> > +	 * never been updated (at least once) since last enqueue time.
> > +	 */
> > +	ue = READ_ONCE(p->se.avg.util_est);
> > +	if (ue.enqueued & UTIL_EST_NEED_UPDATE_FLAG)
> > +		return;
> 
> The name and function seem inverted, if the flag is set, we do _NOT_
> update util_est.

My reading was along the line "when the flag is set we need an
update of util_avg to collect a new util_est sample"...

... but I agree that's confusing... and unnecessary long.

> How about something like UTIL_EST_UNCHANGED ? That would give:

I would prefer UTIL_AVG_UNCHANGED, since the flags is reset when we
have a change in util_avg, thus enabling util_est updates.

> 	/*
> 	 * If the PELT values haven't changed since enqueue time,
> 	 * skip the util_est update.
> 	 */
> 	if (enqueue & UTIL_EST_UNCHANGED)
> 		return;

-- 
#include <best/regards.h>

Patrick Bellasi