linux-kernel - Re: [PATCH] cpufreq: ondemand: Change the calculation of target frequency

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Message-ID: <CAKohpomLkogSHD+5Wobb34qHPnb7_vWE1Xz4K5MD=Q50kOpfuA@mail.gmail.com>
Date:	Mon, 3 Jun 2013 16:54:08 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Stratos Karafotis <stratosk@...aphore.gr>,
	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] cpufreq: ondemand: Change the calculation of target frequency

On 3 June 2013 16:27, Rafael J. Wysocki <rjw@...k.pl> wrote:
> The question is if we want policy->max to re-scale them effectively (i.e. to
> change weights so that the maximum load maps to the highest frequency available
> at the moment) or if we want policy->max to work as a cap (i.e. to map all
> loads above certain value to the maximum frequency available at the moment, so
> that the criteria for selecting the lower frequencies don't change).  In my
> opinion the second option is better, because it means "OK, we can't use some
> high frequencies, but let's not hurt performance for the loads that wouldn't
> require them anyway".  Otherwise, we'll effectively throttle all loads and
> that not only causes performance to drop, but also causes more energy to be
> used overall.

I wouldn't say that I don't agree with you as I do to some extent.

But the question that comes to my mind now is: Why is policy->max reduced
in the first place? User doesn't have control over which freqs to expose, so
available_frequencies will stay the same. The only thing he is capable
of doing is: reduce policy->max.. Which in a way means that.. "I don't want to
use higher frequencies (power, thermal reasons) and I know performance will
go down with it and I don't care for it now."

And this way I feel policy->max isn't a bad choice either.

BUT as you said: policy->max isn't there to say don't be so aggressive now in
increasing frequencies but just only to say, don't go over this frequency..

So, probably we can use cpuinfo.max_freq :)
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