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

From: Sudeep Holla <[email-masked]>
Date: Tue, 29 Jan 2019 15:27:35 +0000

On Mon, Jan 28, 2019 at 04:55:21PM +0000, Quentin Perret wrote:
> From: Dietmar Eggemann <[email-masked]>
>
> 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.

--
Regards,
Sudeep

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