linux-kernel - Re: [PATCH 2/4] Documentation: EM: Switch to micro-Watts scale

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Date:   Tue, 5 Jul 2022 11:10:32 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Cc:     amitk@...nel.org, rui.zhang@...el.com, viresh.kumar@...aro.org,
        rafael@...nel.org, dietmar.eggemann@....com, nm@...com,
        sboyd@...nel.org, sudeep.holla@....com, cristian.marussi@....com,
        matthias.bgg@...il.com, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/4] Documentation: EM: Switch to micro-Watts scale

On 22/06/2022 16:58, Lukasz Luba wrote:
> The EM now uses the micro-Watts scale for the power values. Update
> related documentation to reflect that fact.
> 
> Fix also a problematic sentence in the doc "to:" which triggers test
> scripts complaining about wrong email address.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@....com>

Reviewed-by: Daniel Lezcano <daniel.lezcano@...aro.org>

> ---
>   Documentation/power/energy-model.rst | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst
> index feb257b7f350..ef341be2882b 100644
> --- a/Documentation/power/energy-model.rst
> +++ b/Documentation/power/energy-model.rst
> @@ -20,20 +20,20 @@ possible source of information on its own, the EM framework intervenes as an
>   abstraction layer which standardizes the format of power cost tables in the
>   kernel, hence enabling to avoid redundant work.
>   
> -The power values might be expressed in milli-Watts or in an 'abstract scale'.
> +The power values might be expressed in micro-Watts or in an 'abstract scale'.
>   Multiple subsystems might use the EM and it is up to the system integrator to
>   check that the requirements for the power value scale types are met. An example
>   can be found in the Energy-Aware Scheduler documentation
>   Documentation/scheduler/sched-energy.rst. For some subsystems like thermal or
>   powercap power values expressed in an 'abstract scale' might cause issues.
>   These subsystems are more interested in estimation of power used in the past,
> -thus the real milli-Watts might be needed. An example of these requirements can
> +thus the real micro-Watts might be needed. An example of these requirements can
>   be found in the Intelligent Power Allocation in
>   Documentation/driver-api/thermal/power_allocator.rst.
>   Kernel subsystems might implement automatic detection to check whether EM
>   registered devices have inconsistent scale (based on EM internal flag).
>   Important thing to keep in mind is that when the power values are expressed in
> -an 'abstract scale' deriving real energy in milli-Joules would not be possible.
> +an 'abstract scale' deriving real energy in micro-Joules would not be possible.
>   
>   The figure below depicts an example of drivers (Arm-specific here, but the
>   approach is applicable to any architecture) providing power costs to the EM
> @@ -98,7 +98,7 @@ Drivers are expected to register performance domains into the EM framework by
>   calling the following API::
>   
>     int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
> -		struct em_data_callback *cb, cpumask_t *cpus, bool milliwatts);
> +		struct em_data_callback *cb, cpumask_t *cpus, bool microwatts);
>   
>   Drivers must provide a callback function returning <frequency, power> tuples
>   for each performance state. The callback function provided by the driver is free
> @@ -106,10 +106,10 @@ to fetch data from any relevant location (DT, firmware, ...), and by any mean
>   deemed necessary. Only for CPU devices, drivers must specify the CPUs of the
>   performance domains using cpumask. For other devices than CPUs the last
>   argument must be set to NULL.
> -The last argument 'milliwatts' is important to set with correct value. Kernel
> +The last argument 'microwatts' is important to set with correct value. Kernel
>   subsystems which use EM might rely on this flag to check if all EM devices use
>   the same scale. If there are different scales, these subsystems might decide
> -to: return warning/error, stop working or panic.
> +to return warning/error, stop working or panic.
>   See Section 3. for an example of driver implementing this
>   callback, or Section 2.4 for further documentation on this API
>   
> @@ -137,7 +137,7 @@ The .get_cost() allows to provide the 'cost' values which reflect the
>   efficiency of the CPUs. This would allow to provide EAS information which
>   has different relation than what would be forced by the EM internal
>   formulas calculating 'cost' values. To register an EM for such platform, the
> -driver must set the flag 'milliwatts' to 0, provide .get_power() callback
> +driver must set the flag 'microwatts' to 0, provide .get_power() callback
>   and provide .get_cost() callback. The EM framework would handle such platform
>   properly during registration. A flag EM_PERF_DOMAIN_ARTIFICIAL is set for such
>   platform. Special care should be taken by other frameworks which are using EM


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