linux-kernel - Re: [PATCH 1/3] sched/fair: Prepare variables for increased precision of EAS estimated energy

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Date:   Wed, 7 Jul 2021 11:29:32 +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 11:11 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
precision makes more sense for internal EAS calculation. I don't
force platforms to report 1uW power, I just want to operate on
it internally. PowerCap and DTPM also operate internally on 1uW,
so it's not that unrealistic that some kernel components want
better resolution.

But as Peter suggested, we might skip 32bit platforms for this issue.
I have to discussed this internally.