linux-kernel - Re: [RFC PATCH v3 03/10] PM: Introduce an Energy Model management framework

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Date:   Wed, 6 Jun 2018 16:29:51 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>, peterz@...radead.org,
        rjw@...ysocki.net, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        mingo@...hat.com, morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joelaf@...gle.com,
        smuckle@...gle.com, adharmap@...cinc.com, skannan@...cinc.com,
        pkondeti@...eaurora.org, edubezval@...il.com,
        srinivas.pandruvada@...ux.intel.com, currojerez@...eup.net,
        javi.merino@...nel.org
Subject: Re: [RFC PATCH v3 03/10] PM: Introduce an Energy Model management
 framework

On Wednesday 06 Jun 2018 at 17:20:00 (+0200), Juri Lelli wrote:
> > > This brings me to another question. Let's say there are multiple users of
> > > the Energy Model in the system. Shouldn't the units of frequency and power
> > > not standardized, maybe Mhz and mW?
> > > The task scheduler doesn't care since it is only interested in power diffs
> > > but other user might do.
> > 
> > So the good thing about specifying units is that we can probably assume
> > ranges on the values. If the power is in mW, assuming that we're talking
> > about a single CPU, it'll probably fit in 16 bits. 65W/core should be
> > a reasonable upper-bound ?
> > But there are also vendors who might not be happy with disclosing absolute
> > values ... These are sometimes considered sensitive and only relative
> > numbers are discussed publicly. Now, you can also argue that we already
> > have units specified in IPA for ex, and that it doesn't really matter if
> > a driver "lies" about the real value, as long as the ratios are correct.
> > And I guess that anyone can do measurement on the hardware and get those
> > values anyway. So specifying a unit (mW) for the power is probably a
> > good idea.
> 
> Mmm, I remember we fought quite a bit while getting capacity-dmpis-mhz
> binding accepted, and one of the musts was that the values were going to
> be normalized. So, normalized power values again maybe?

Hmmm, that's a very good point ... There should be no problems on the
scheduler side -- we're only interested in correct ratios. But I'm not
sure on the thermal side ... I will double check that.

Javi, Viresh, Eduardo: any thoughts about this ?

Thanks !
Quentin