linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Change the calculation of next pstate

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Date:	Tue, 29 Apr 2014 19:34:46 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Dirk Brandewie <dirk.j.brandewie@...el.com>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpufreq: intel_pstate: Change the calculation of next
 pstate

On 29/04/2014 07:58 πμ, Viresh Kumar wrote:
> Cc'd Dirk,
> 
> On 28 April 2014 03:42, Stratos Karafotis <stratosk@...aphore.gr> wrote:
>> Currently the driver calculates the next pstate proportional to
>> core_busy factor and reverse proportional to current pstate.
>>
>> Change the above method and calculate the next pstate independently
>> of current pstate.
> 
> We must mention why the change is required.
> 

Hi Viresh,

Actually, I can't say that it's required. :)
I just believe that calculation of next p-state should be independent
from current one. In my opinion we can't scale the load across different
p-states, because it's not always equivalent.

For example suppose a load of 100% because of a tight for loop in the
current p-state. It will be also a 100% load in any other p-state.
It will be wrong if we scale the load in the calculation formula
according to the current p-state.

I included the test results in the change log to point out an improvement
because of this patch.

I will enrich more the change log as you suggested.

Thanks,
Stratos Karafotis

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