linux-kernel - Re: [PATCH v2 14/17] Documentation: EM: Add a new section about the design

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Date:   Mon, 3 Jul 2023 17:09:46 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     rui.zhang@...el.com, amit.kucheria@...durent.com,
        amit.kachhap@...il.com, daniel.lezcano@...aro.org,
        viresh.kumar@...aro.org, len.brown@...el.com, pavel@....cz,
        Pierre.Gondois@....com, ionela.voinescu@....com,
        rostedt@...dmis.org, mhiramat@...nel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        rafael@...nel.org
Subject: Re: [PATCH v2 14/17] Documentation: EM: Add a new section about the
 design



On 5/30/23 11:33, Dietmar Eggemann wrote:
> On 12/05/2023 11:57, Lukasz Luba wrote:
>> Add a new section 'Design' which covers the information about Energy
>> Model. It contains the design decisions, describes models and how they
>> reflect the reality. Add description of the basic const. EM. Change the
>> other section IDs.
> 
> I would vote for coalescing the 4 doc patches into 1.

OK, I can make that. I will be a big one patch, though.

> 
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> ---
>>   Documentation/power/energy-model.rst | 36 +++++++++++++++++++++-------
>>   1 file changed, 27 insertions(+), 9 deletions(-)
>>
>> diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst
>> index ef341be2882b..e97c7f18d8bd 100644
>> --- a/Documentation/power/energy-model.rst
>> +++ b/Documentation/power/energy-model.rst
>> @@ -72,16 +72,34 @@ required to have the same micro-architecture. CPUs in different performance
>>   domains can have different micro-architectures.
>>   
>>   
>> -2. Core APIs
>> +2. Design
>> +-----------------
>> +
>> +2.1 Basic EM
>> +^^^^^^^^^^^^
> 
> Can we make sure that people get the relation between 'basic' and
> 'default' easier?
> 
> It should be obvious that `pd->default_table->state` refers to this
> `basic (const.) EM. Using the same identifier always helps in this
> situation.

OK, how about adding this:
"The basic EM is built around const. power information for each
performance state, which is accessible in:
'dev->em_pd->default_table->state'. This model can be derived based..."

> 
>> +
>> +The basic EM is built around const. power information for each performance
>> +state. This model can be derived based on power measurements of the device
>> +e.g. CPU while running some benchmark. The benchmark might be integer heavy
>> +or floating point computation with a data set fitting into the CPU cache or
>> +registers. Bare in mind that this model might not be covering all possible
>> +workloads running on CPUs. Thus, please run a few different benchmarks and
>> +verify with some real workloads your power model values. The power variation
>> +due to the workload instruction mix and data set is not modeled.
>> +Also static power which can change during runtime due to variation of SOC
>> +temperature is not modeled in EM.
>> +
>> +