linux-kernel - Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator

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Message-ID: <20180802122629.GU2476@hirez.programming.kicks-ass.net>
Date:   Thu, 2 Aug 2018 14:26:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...hat.com, dietmar.eggemann@....com,
        morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joel@...lfernandes.org,
        smuckle@...gle.com, adharmap@...cinc.com, skannan@...cinc.com,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point
 indicator

On Tue, Jul 24, 2018 at 01:25:16PM +0100, Quentin Perret wrote:
> @@ -5100,8 +5118,17 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
>  		update_cfs_group(se);
>  	}
>  
> -	if (!se)
> +	if (!se) {
>  		add_nr_running(rq, 1);
> +		/*
> +		 * The utilization of a new task is 'wrong' so wait for it
> +		 * to build some utilization history before trying to detect
> +		 * the overutilized flag.
> +		 */
> +		if (flags & ENQUEUE_WAKEUP)
> +			update_overutilized_status(rq);
> +
> +	}
>  
>  	hrtick_update(rq);
>  }

That is a somewhat dodgy hack. There is no guarantee what so ever that
when the task wakes next its history is any better. The comment doesn't
reflect this I feel.