linux-kernel - Re: [PATCH] sched/fair: util_est: fast ramp-up EWMA on utilization increases

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Date:   Mon, 1 Jul 2019 09:53:50 +0100
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Douglas Raillard <douglas.raillard@....com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH] sched/fair: util_est: fast ramp-up EWMA on utilization
 increases

On 30-Jun 10:43, Vincent Guittot wrote:
> On Fri, 28 Jun 2019 at 16:10, Patrick Bellasi <patrick.bellasi@....com> wrote:
> > On 28-Jun 15:51, Vincent Guittot wrote:
> > > On Fri, 28 Jun 2019 at 14:38, Peter Zijlstra <peterz@...radead.org> wrote:
> > > > On Fri, Jun 28, 2019 at 11:08:14AM +0100, Patrick Bellasi wrote:
> > > > > On 26-Jun 13:40, Vincent Guittot wrote:

Hi Vincent,

[...]

> > > AFAICT, it's not related to the time-scaling
> > >
> > > In fact the big 1st activation happens because task runs at low OPP
> > > and hasn't enough time to finish its running phase before the time to
> > > begin the next one happens. This means that the task will run several
> > > computations phase in one go which is no more a 75% task.
> >
> > But in that case, running multiple activations back to back, should we
> > not expect the util_avg to exceed the 75% mark?
> 
> But task starts with a very low value and Pelt needs time to ramp up.

Of course...

[...]

> > > Once cpu reaches a high enough OPP that enable to have sleep phase
> > > between each running phases, the task load tracking comes back to the
> > > normal slope increase (the one that would have happen if task would
> > > have jump from 5% to 75% but already running at max OPP)
> >
> >
> > Indeed, I can see from the plots a change in slope. But there is also
> > that big drop after the first big activation: 375 units in 1.1ms.
> >
> > Is that expected? I guess yes, since we fix the clock_pelt with the
> > lost_idle_time.

... but, I guess Peter was mainly asking about the point above: is
that "big" drop after the first activation related to time-scaling or
not?

Cheers,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi