linux-kernel - Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler utilization data

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Date:	Thu, 10 Mar 2016 11:30:08 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Juri Lelli <juri.lelli@....com>,
	mturquette <mturquette@...libre.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steve Muckle <steve.muckle@...aro.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler
 utilization data

On Thu, Mar 10, 2016 at 05:23:54PM +0700, Vincent Guittot wrote:

> > No, since its a compile time thing, we can simply do:
> >
> > #ifdef arch_scale_freq_capacity
> >         next_freq = (1 + 1/n) * max_freq * (util / max)
> > #else
> >         next_freq = (1 + 1/n) * current_freq * (util_raw / max)
> > #endif
> 
> selecting formula at compilation is clearly better. I wrongly thought that
> it can't be accepted as a solution.

Well, its bound to get more 'interesting' since I forse implementations
not always actually doing the invariant thing.

Take for example the thing I send:

  lkml.kernel.org/r/20160303162829.GB6375@...ns.programming.kicks-ass.net

it both shows why you cannot talk about current_freq but also that the
above needs a little more help (for the !X86_FEATURE_APERFMPERF case).

But the !arch_scale_freq_capacity case should indeed be that simple.