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

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Message-ID: <53719C98.1010103@semaphore.gr>
Date:	Tue, 13 May 2014 07:16:24 +0300
From:	Stratos Karafotis <stratosk@...aphore.gr>
To:	Yuyang Du <yuyang.du@...el.com>
CC:	Dirk Brandewie <dirk.brandewie@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Dirk Brandewie <dirk.j.brandewie@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Doug Smythies <dsmythies@...us.net>
Subject: Re: [RFC PATCH] cpufreq: intel_pstate: Change the calculation of
 next pstate

On 12/05/2014 11:01 μμ, Yuyang Du wrote:
> On Tue, May 13, 2014 at 06:59:42AM +0300, Stratos Karafotis wrote:
>> Hi,
>>
>> On 12/05/2014 10:34 μμ, Yuyang Du wrote:
>>> On Mon, May 12, 2014 at 11:30:03PM +0300, Stratos Karafotis wrote:
>>>> On 09/05/2014 05:56 μμ, Stratos Karafotis wrote:
>>>>
>>>> Next performance state = min_perf + (max_perf - min_perf) * load / 100
>>>>
>>> Hi,
>>>
>>> This formula is fundamentally broken. You need to associate the load with its
>>> frequency.
>>
>> Could you please explain why is it broken? I think the load should be
>> independent from the current frequency.
> 
> Why independent? The load not (somewhat) determined by that?
> 
> 

Maybe, in some cases yes. But not always.
For example, please consider a CPU running a tight "for" loop in 100MHz
for a couple of seconds. This produces a load of 100%.
It will produce the same load (100%) in any other frequency.


Stratos
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