linux-kernel - Re: [RFCv5 PATCH 40/46] sched/cpufreq_sched: compute freq_new based on capacity_orig

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Message-ID: <20150816202401.GJ10304@worktop.programming.kicks-ass.net>
Date:	Sun, 16 Aug 2015 22:24:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michael Turquette <mturquette@...libre.com>
Cc:	Morten Rasmussen <morten.rasmussen@....com>, mingo@...hat.com,
	vincent.guittot@...aro.org, daniel.lezcano@...aro.org,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	yuyang.du@...el.com, rjw@...ysocki.net,
	Juri Lelli <Juri.Lelli@....com>, sgurrappadi@...dia.com,
	pang.xunlei@....com.cn, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [RFCv5 PATCH 40/46] sched/cpufreq_sched: compute freq_new based
 on capacity_orig_of()

On Sat, Aug 15, 2015 at 09:03:33PM -0700, Michael Turquette wrote:
> Quoting Peter Zijlstra (2015-08-15 05:46:38)
> > On Tue, Jul 07, 2015 at 07:24:23PM +0100, Morten Rasmussen wrote:
> > > diff --git a/kernel/sched/cpufreq_sched.c b/kernel/sched/cpufreq_sched.c
> > > index 2968f3a..7071528 100644
> > > --- a/kernel/sched/cpufreq_sched.c
> > > +++ b/kernel/sched/cpufreq_sched.c
> > > @@ -184,7 +184,7 @@ void cpufreq_sched_set_cap(int cpu, unsigned long capacity)
> > >               goto out;
> > >  
> > >       /* Convert the new maximum capacity request into a cpu frequency */
> > > -     freq_new = capacity * policy->max >> SCHED_CAPACITY_SHIFT;
> > > +     freq_new = (capacity * policy->max) / capacity_orig_of(cpu);
> > >  
> > >       /* No change in frequency? Bail and return current capacity. */
> > >       if (freq_new == policy->cur)
> > 
> > Can't we avoid exporting that lot by simply passing in the right values
> > to begin with?
> 
> By "right value" do you mean, "pass the frequency from cfs"?

Nah, just maybe: (capacity << SCHED_CAPACITY_SHIFT) / capacity_orig_of()
such that you don't have to export that knowledge to this thing.
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