linux-kernel - Re: [PATCH] sched/fair: Introduce fits

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Message-ID: <20190618074728.gf6wugkbndhhcqql@vireshk-i7>
Date:   Tue, 18 Jun 2019 13:17:28 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Quentin Perret <quentin.perret@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] sched/fair: Introduce fits_capacity()

On 18-06-19, 09:26, Rafael J. Wysocki wrote:
> On Tue, Jun 18, 2019 at 5:12 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > +Rafael
> >
> > On 17-06-19, 17:02, Peter Zijlstra wrote:
> > > On Thu, Jun 06, 2019 at 08:22:04AM +0530, Viresh Kumar wrote:
> > > > Hmm, even if the values are same currently I am not sure if we want
> > > > the same for ever. I will write a patch for it though, if Peter/Rafael
> > > > feel the same as you.
> > >
> > > Is it really the same variable or just two numbers that happen to be the
> > > same?
> >
> > In both cases we are trying to keep the load under 80% of what can be supported.
> > But I am not sure of the answer to your question.
> >
> > Maybe Rafael knows :)
> 
> Which variable?

Schedutil multiplies the target frequency by 1.25 (20% more capacity eventually)
to get enough room for more load and similar thing is done in fair.c at several
places to see if the new task can fit in a runqueue without overloading it.

Quentin suggested to use common code for this calculation and that is what is
getting discussed here.

-- 
viresh