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Re: [PATCH v6 1/8] Documentation: arm: define DT cpu capacity-dmips-mhz bindings

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On Tue, Jul 19, 2016 at 01:40:41PM +0100, Juri Lelli wrote:
> ARM systems may be configured to have cpus with different power/performance
> characteristics within the same chip. In this case, additional information
> has to be made available to the kernel (the scheduler in particular) for it
> to be aware of such differences and take decisions accordingly.
> 
> Therefore, this patch aims at standardizing cpu capacities device tree
> bindings for ARM platforms. Bindings define cpu capacity-dmips-mhz
> parameter, to allow operating systems to retrieve such information from
> the device tree and initialize related kernel structures, paving the way
> for common code in the kernel to deal with heterogeneity.
> 
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Pawel Moll <pawel.moll@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
> Cc: Kumar Gala <galak@codeaurora.org>
> Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
> Cc: Olof Johansson <olof@lixom.net>
> Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
> Cc: Paul Walmsley <paul@pwsan.com>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Cc: Chen-Yu Tsai <wens@csie.org>
> Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
> Cc: devicetree@vger.kernel.org
> Signed-off-by: Juri Lelli <juri.lelli@arm.com>
> ---
> 
> Changes from v1:
>  - removed section regarding capacity-scale
>  - added information regarding normalization
> 
> Changes from v4:
>  - binding changed to capacity-dmips-mhz
>  - sections and changelod updated accordingly
> 
> Changes from v5:
>  - addressed Mark and Vincent comments
> ---
>  .../devicetree/bindings/arm/cpu-capacity.txt       | 236 +++++++++++++++++++++
>  Documentation/devicetree/bindings/arm/cpus.txt     |  10 +
>  2 files changed, 246 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/cpu-capacity.txt

I guess I'm okay with the scaled values, so:

Acked-by: Rob Herring <robh@kernel.org>

[...]

> +Example 2 (ARM 32-bit, 4-cpu system, two clusters,
> +	   cpus 0,1@1GHz, cpus 2,3@500MHz):
> +capacities-dmips-mhz are scaled w.r.t. 2 (cpu@0 and cpu@1), this means that first
> +cpu@0 and cpu@1 are twice fast than cpu@2 and cpu@3 (at the same frequency)

This example is a bit confusing with both the capacity and frequency 
being half. I also find it a bit unrealistic to have a 2x performance 
difference on the same micro arch. But it is all just an example...

Rob

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[PATCH v6 0/8] CPUs capacity information for heterogeneous systems Juri Lelli <juri.lelli@arm.com> - 2016-07-19 14:50 +0200
  [PATCH v6 3/8] arm, dts: add TC2 cpu capacity-dmips-mhz information Juri Lelli <juri.lelli@arm.com> - 2016-07-19 14:50 +0200
  [PATCH v6 4/8] arm64: parse cpu capacity-dmips-mhz from DT Juri Lelli <juri.lelli@arm.com> - 2016-07-19 14:50 +0200
  [PATCH v6 1/8] Documentation: arm: define DT cpu capacity-dmips-mhz bindings Juri Lelli <juri.lelli@arm.com> - 2016-07-19 14:50 +0200
    Re: [PATCH v6 1/8] Documentation: arm: define DT cpu  capacity-dmips-mhz bindings Rob Herring <robh@kernel.org> - 2016-07-20 21:00 +0200
      Re: [PATCH v6 1/8] Documentation: arm: define DT cpu  capacity-dmips-mhz bindings Juri Lelli <juri.lelli@arm.com> - 2016-07-21 13:50 +0200
  [PATCH v6 6/8] arm64, dts: add Juno r2 cpu capacity-dmips-mhz information Juri Lelli <juri.lelli@arm.com> - 2016-07-19 14:50 +0200

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