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

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Message-ID: <20180308094830.GK25201@hirez.programming.kicks-ass.net>
Date:   Thu, 8 Mar 2018 10:48:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
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 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.

How about something like UTIL_EST_UNCHANGED ? That would give:

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