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Date: Wed, 7 Jul 2021 12:02:19 +0100
From: Lukasz Luba <lukasz.luba@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: linux-kernel <linux-kernel@...r.kernel.org>,
Chris Redpath <Chris.Redpath@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Morten Rasmussen <morten.rasmussen@....com>,
Quentin Perret <qperret@...gle.com>,
"open list:THERMAL" <linux-pm@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
Viresh Kumar <viresh.kumar@...aro.org>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>, segall@...gle.com,
Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
CCj.Yeh@...iatek.com
Subject: Re: [PATCH 1/3] sched/fair: Prepare variables for increased precision
of EAS estimated energy
On 7/7/21 11:50 AM, Vincent Guittot wrote:
> On Wed, 7 Jul 2021 at 12:41, Lukasz Luba <lukasz.luba@....com> wrote:
>>
>>
>>
>> On 7/7/21 11:32 AM, Vincent Guittot wrote:
>>> On Wed, 7 Jul 2021 at 12:29, Lukasz Luba <lukasz.luba@....com> wrote:
>>>>
>>>>
>>>>
>>>> On 7/7/21 11:11 AM, Vincent Guittot wrote:
>>>>> On Wed, 7 Jul 2021 at 12:06, Lukasz Luba <lukasz.luba@....com> wrote:
>>>>>>
>>>>
>>>> [snip]
>>>>
>>>>>> No. It's in 0.1uW scale, so 800Watts. Which is 16 CPUs * 64Watts
>>>>>
>>>>> Oh! you want 0.1uW precision .... This doesn't seem realistic at all.
>>>>> I'm not even sure that the power model can even reach an accuracy of
>>>>> 1mW
>>>>>
>>>>
>>>> True, the EM is registering platform with 1mW precision, but 1uW
>>>
>>> Do you mean 1uW or 0.1uW ?
>>
>> In this patch set I've proposed 0.1uW, but I'm open to drop one
>> order of magnitude. The 1uW still be good.
>
> I don't want to underestimate the capabilities of the power model but
> I don't see which benefit you will get with 0.1uW precision
> With a 1uW precision the long type currently used for the returned
> value is fine for 32bits machine AFAICT
>
For 1uW and 1.2Watts for one core, 4 CPUs in cluster we get:
(1200 * 1000) * (4 * 1024) = ~4.9bln
so it would need div 64 version
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