Re: [PATCH 1/2] docs: Clarify abstract scale usage for power values in Energy Model

Lukasz Luba
2020-09-30T08:25:27Z

Hi Douglas,

On 9/30/20 12:53 AM, Doug Anderson wrote:
> Hi,
>
> On Tue, Sep 29, 2020 at 5:16 AM Lukasz Luba <lukasz.luba@arm.com> wrote:
>>
>> The Energy Model (EM) can store power values in milli-Watts or in abstract
>> scale. This might cause issues in the subsystems which use the EM for
>> estimating the device power, such as:
>> - mixing of different scales in a subsystem which uses multiple
>> (cooling) devices (e.g. thermal Intelligent Power Allocation (IPA))
>> - assuming that energy [milli-Joules] can be derived from the EM power
>> values which might not be possible since the power scale doesn't have to
>> be in milli-Watts
>>
>> To avoid misconfiguration add the needed documentation to the EM and
>> related subsystems: EAS and IPA.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
>> ---
>> .../driver-api/thermal/power_allocator.rst | 8 ++++++++
>> Documentation/power/energy-model.rst | 13 +++++++++++++
>> Documentation/scheduler/sched-energy.rst | 5 +++++
>> 3 files changed, 26 insertions(+)
>
> I haven't read through these files in massive detail, but the quick
> skim makes me believe that your additions seem sane. In general, I'm
> happy with documenting reality, thus:
>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>

Thank you for the review.

>
> I will note: you haven't actually updated the device tree bindings.
> Thus, presumably, anyone who is specifying these numbers in the device
> tree is still supposed to specify them in a way that mW can be
> recovered, right? Said another way: nothing about your patches makes
> it OK to specify numbers in device trees using an "abstract scale",
> right?

For completeness, we are talking here about the binding from:
Documentation/devicetree/bindings/arm/cpus.yaml
which is 'dynamic-power-coefficient'. Yes, it stays untouched, also the
unit (uW/MHz/V^2) which then allows to have mW in the power
values in the EM.

Regards,
Lukasz