linux-kernel - Re: [PATCH 6/7] arm64: dts: juno: Add cpu dynamic-power-coefficient information

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Date:   Wed, 30 Jan 2019 10:23:13 +0000
From:   Quentin Perret <quentin.perret@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     rjw@...ysocki.net, viresh.kumar@...aro.org, liviu.dudau@....com,
        lorenzo.pieralisi@....com, robh+dt@...nel.org,
        mark.rutland@....com, nm@...com, sboyd@...nel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        dietmar.eggemann@....com, mka@...omium.org
Subject: Re: [PATCH 6/7] arm64: dts: juno: Add cpu dynamic-power-coefficient
 information

On Tuesday 29 Jan 2019 at 15:27:35 (+0000), Sudeep Holla wrote:
> On Mon, Jan 28, 2019 at 04:55:21PM +0000, Quentin Perret wrote:
> > From: Dietmar Eggemann <dietmar.eggemann@....com>
> >
> > A CPUfreq driver, like the scpi driver used on Juno boards, which
> > provide the Energy Model with power cost information via the PM_OPP
> > of_dev_pm_opp_get_cpu_power() function, do need the
> > dynamic-power-coefficient (C) in the device tree.
> >
> > Method used to obtain the C value:
> > C is computed by measuring energy (E) consumption of a frequency domain
> > (FD) over a 10s runtime (t) sysbench workload running at each Operating
> > Performance Point (OPP) affine to 1 or 2 CPUs of that FD while the other
> > CPUs of the system are hotplugged out.
> > By definition all CPUs of a FD have the the same micro-architecture. An
> > OPP is characterized by a certain frequency (f) and voltage (V) value.
> > The corresponding power values (P) are calculated by dividing the delta
> > of the E values between the runs with 2 and 1 CPUs by t.
> >
> > With n data tuples (P, f, V), n equal to number of OPPs for this
> > frequency domain, we can solve C by:
> >
> > P = Pstat + Pdyn
> >
> > P = Pstat + CV²f
> >
> > Cx = (Px - P1)/(Vx²fx - V1²f1) with x = {2, ..., n}
> >
> > The C value is the arithmetic mean out of {C2, ..., Cn}.
> >
> > Since DVFS is broken on Juno r1, no dynamic-power-coefficient
> > information has been added to its dts file.
> >
> 
> Since the binding for "dynamic-power-coefficient" property already exist,
> and I don't see any dependency for this and the next patch(TC2) on this
> series, I will apply them. Please shout if for any reason that's not true.

Thanks Sudeep !
Quentin