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

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Message-ID: <CAKohpom3AA3xCHqZ-TeWgOgwM-=CQxd0XSAmKp85mR-p6txmcg@mail.gmail.com>
Date:	Mon, 3 Jun 2013 11:41:25 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stratos Karafotis <stratosk@...aphore.gr>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, 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 1 June 2013 21:36, Stratos Karafotis <stratosk@...aphore.gr> wrote:
> On 06/01/2013 05:56 PM, Viresh Kumar wrote:

>> Even removal of __cpufreq_driver_getavg() should be done in a separate
>> patch, so that it can be reverted easily if required later.
>
> Thanks, Viresh. I will do the removal of that function in a seperate patch.
> Should I use a third patch for it? Or should I include it in the patch which
> will remove APERF/MPERF support?

Maybe a third patch would be more cleaner.

>> Why are you changing it to cpuinfo.max_freq?? This is fixed once a driver is
>> initialized.. but user may request a lower max freq for a governor or policy.
>> Which is actually reflected in policy->max I believe.
>
> My initial thought is to have a linear function to calculate the target freq
> proportional to load: (I will use 'C' as the function's slope as Rafael used it)
>
> freq_target = C * load
>
> For simplicity, let's assume that load is between 0 and 1 as initially is calculated
> in governor.
> Ideally,  for a load = 0, we should have freq_target = 0 and for load = 1,
> freq_target = cpuinfo.max
>
> So, the slope C = cpuinfo.max
>
> I think, it's matter of definition about what policy->min and policy->max can do.
> Should they change the slope C? Or only limit freq_target?
> I don't think that the policy->max (or min) should affect HOW (slope C) governor
> calculates freq_target but only limit the calculated result.
>
> Maybe, we could have separate tunables to a affect the slope C.
>
> If I'm wrong about the definition of policy->min, policy->max, I would change
> the code accordingly.

Lets discuss that in reply to Rafael's mail.

>> As, if load is over 95, then even policy->max * 95 / 100 will even give almost
>> the same freq.
>>
>
> I thought that too. But maybe user selects a lower value for up_threshold.
> (For example, up_threshold = 60). In my opinion, we have to keep up_theshold,
> to give the possibility to user to have max freq with small loads.

Yes... good point.
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