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

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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@xxxxxxx> 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@xxxxxxx>
---
  .../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@xxxxxxxxxxxx>

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



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