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

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Date:	Thu, 3 Mar 2016 16:38:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler
 utilization data

On Thu, Mar 03, 2016 at 03:01:15PM +0100, Vincent Guittot wrote:
> > In case a more formal derivation of this formula is needed, it is
> > based on the following 3 assumptions:
> >
> > (1) Performance is a linear function of frequency.
> > (2) Required performance is a linear function of the utilization ratio
> > x = util/max as provided by the scheduler (0 <= x <= 1).
> 
> Just to mention that the utilization that you are using, varies with
> the frequency which add another variable in your equation

Right, x86 hasn't implemented arch_scale_freq_capacity(), so the
utilization values we use are all over the map. If we lower freq, the
util will go up, which would result in us bumping the freq again, etc..