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

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Date:	Sat, 15 Aug 2015 21:03:33 -0700
From:	Michael Turquette <mturquette@...libre.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	"Morten Rasmussen" <morten.rasmussen@....com>
Cc:	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()

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"?

If that is what you mean, then the answer is "yes". But it also means
that cfs will need access to either:

1) the cpu frequncy-domain topology described in struct cpufreq.cpus
OR
2) duplicate that frequency-domain knowledge, perhaps in sched_domain

If that isn't what you mean by "right value" then let me know.

Regards,
Mike

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