Re: [PATCH v6 0/3] Make IPA use PM_EM

[Daniel Lezcano <daniel.lezcano@linaro.org>]

Hi Rui,

is it possible to merge these patches? They are acked-by since May.

Thanks

  -- Daniel


On 01/08/2019 14:46, Quentin Perret wrote:
> Changes in v6
> *************
>  - Added Daniel's and Viresh's Acked-by to all patches
> 
> Changes in v5:
> **************
>  - Changed patch 02 to guard IPA-specific code in cpu_cooling.c with
>    appropriate ifdefery (Daniel)
>  - Rebased on 5.2-rc2
> 
> Changes in v4:
> **************
>  - Added Viresh's Acked-by to all 3 patches
>  - Improved commit message of patch 3/3 to explain how it has no
>    functional impact on existing users (Eduardo)
> 
> Changes in v3:
> **************
>  - Changed warning message for unordered tables to something more
>    explicit (Viresh)
>  - Changed WARN() into a pr_err() for consistency
> 
> Changes in v2:
> **************
>  - Fixed patch 01/03 to actually enable CONFIG_ENERGY_MODEL
>  - Added "depends on ENERGY_MODEL" to IPA (Daniel)
>  - Added check to bail out if the freq table is unsorted (Viresh)
> 
> Cover letter:
> *************
> 
> The Intelligent Power Allocator (IPA) thermal governor uses an Energy
> Model (or EM) of the CPUs to re-distribute the power budget. To do so,
> it builds a table of <frequency, power> tuples where the power values
> are computed using the 'dynamic-power-coefficient' DT property. All of
> this is done in and only for the thermal subsystem, and more
> specifically for CPUs -- the power of other types of devices is obtained
> differently.
> 
> Recently, the CPU scheduler has seen the introduction of Energy Aware
> Scheduling (EAS) patches, which also rely on an EM of the CPUs. This EM,
> however, is managed by an independent framework, called PM_EM, aimed to
> be used by all kernel subsystems interested in the power consumed by
> CPUs, and not only the scheduler.
> 
> This patch series follows this logic and removes the (now redundant)
> thermal-specific EM computation code to migrate IPA to use PM_EM
> instead.
> 
> Doing so should have no visible functional impact for existing users of
> IPA since:
> 
>  - during the 5.1 development cycle, a series of patches [1] introduced
>    in PM_OPP some infrastructure (dev_pm_opp_of_register_em()) enabling
>    the registration of EMs in PM_EM using the DT property used by IPA;
> 
>  - the existing upstream cpufreq drivers marked with the
>    'CPUFREQ_IS_COOLING_DEV' flag all call dev_pm_opp_of_register_em(),
>    which means they all support PM_EM (the only two exceptions are
>    qoriq-cpufreq which doesn't in fact use an EM and scmi-cpufreq which
>    already supports PM_EM without using the PM_OPP infrastructurei
>    because it read power costs directly from firmware);
> 
> So, migrating IPA to using PM_EM should effectively be just plumbing
> since for the existing IPA users the PM_EM tables will contain the
> exact same power values that IPA used to compute on its own until now.
> The only new dependency is to compile in CONFIG_ENERGY_MODEL.
> 
> Why is this migration still a good thing ? For three main reasons.
> 
>  1. it removes redundant code;
> 
>  2. it introduces an abstraction layer between IPA and the EM
>     computation. PM_EM offers to EAS and IPA (and potentially other
>     clients) standardized EM tables and hides 'how' these tables have
>     been obtained. PM_EM as of now supports power values either coming
>     from the 'dynamic-power-coefficient' DT property or obtained
>     directly from firmware using SCMI. The latter is a new feature for
>     IPA and that comes 'for free' with the migration. This will also be
>     true in the future every time PM_EM gets support for other ways of
>     loading the EM. Moreover, PM_EM is documented and has a debugfs
>     interface which should help adding support for new platforms.
> 
>  3. it builds a consistent view of the EM of CPUs across kernel
>     subsystems, which is a pre-requisite for any kind of future work
>     aiming at a smarter power allocation using scheduler knowledge about
>     the system for example.
> 
> [1] https://lore.kernel.org/lkml/20190204110952.16025-1-quentin.perret@arm.com/
> 
> 
> Quentin Perret (3):
>   arm64: defconfig: Enable CONFIG_ENERGY_MODEL
>   thermal: cpu_cooling: Make the power-related code depend on IPA
>   thermal: cpu_cooling: Migrate to using the EM framework
> 
>  arch/arm64/configs/defconfig  |   1 +
>  drivers/thermal/Kconfig       |   1 +
>  drivers/thermal/cpu_cooling.c | 428 ++++++++++++++--------------------
>  3 files changed, 178 insertions(+), 252 deletions(-)
> 


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