linux-kernel - Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in Energy Model, EAS and IPA

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Message-ID: <20201016130905.GA2426638@google.com>
Date:   Fri, 16 Oct 2020 14:09:05 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Lukasz Luba <lukasz.luba@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Amit Kucheria <amitk@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Dietmar Eggemann <Dietmar.Eggemann@....com>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        "Nayak, Rajendra" <rnayak@...eaurora.org>
Subject: Re: [PATCH v2 0/3] Clarify abstract scale usage for power values in
 Energy Model, EAS and IPA

On Friday 16 Oct 2020 at 14:50:29 (+0200), Daniel Lezcano wrote:
> On 16/10/2020 14:18, Quentin Perret wrote:
> > On Friday 16 Oct 2020 at 13:48:33 (+0200), Daniel Lezcano wrote:
> >> If the SCMI is returning abstract numbers, the thermal IPA governor will
> >> use these numbers as a reference to mitigate the temperature at the
> >> specified sustainable power which is expressed in mW in the DT. So it
> >> does not work and we can not detect such conflict.
> >>
> >> That is why I'm advocating to keep mW for the energy model and make the
> >> SCMI and DT power numbers incompatible.
> > 
> > I think it's fair to say SCMI-provided number should only be compared to
> > other SCMI-provided numbers, so +1 on that. But what I don't understand
> > is why specifying the EM in mW helps with that?
> 
> It is already specified in mW. I'm just saying to not add the
> 'scale'/'abstract'/'bogoWatt' in the documentation.
> 
> > Can we not let the providers specify the unit? 
> 
> Yes, it is possible but the provider must give the 'unit' and the energy
> model must store this information along with the "power" numbers, so we
> can compare apple with apple.
> 
> Today, the energy model is using the mW unit only and the providers are
> not telling the 'unit', so both are missing.
> 
> Because both are missing, it does not make sense to talk about
> 'abstract' values in the energy model documentation until the above is
> fixed.

Right, so that sounds like a reasonable way forward with this series.

Lukasz would you be able to re-spin this with a first patch that allows
the EM provider to specify a unit? And perhaps we could use Doug's idea
for the sustained power DT binding and allow specifying a unit
explicitly there too, so we're sure to compare apples with apples.

Thanks,
Quentin