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Date: Tue, 13 May 2014 07:16:24 +0300
From: Stratos Karafotis <stratosk@semaphore.gr>
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To: Yuyang Du <yuyang.du@intel.com>
CC: Dirk Brandewie <dirk.brandewie@gmail.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Dirk Brandewie <dirk.j.brandewie@intel.com>,
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        LKML <linux-kernel@vger.kernel.org>,
        Doug Smythies <dsmythies@telus.net>
Subject: Re: [RFC PATCH] cpufreq: intel_pstate: Change the calculation of
 next pstate
References: <5368255D.3090207@semaphore.gr> <536BEE89.3040602@gmail.com> <536CECB4.1090109@semaphore.gr> <53712F4B.7000101@semaphore.gr> <20140512193453.GB9351@intel.com> <537198AE.3050100@semaphore.gr> <20140512200140.GA10676@intel.com>
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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