linux-kernel - Re: [PATCH v5 00/23] Introduce runtime modifiable Energy Model

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Message-ID: <ccca81be-eb3e-4f52-a973-22f128ca07ba@arm.com>
Date:   Wed, 13 Dec 2023 12:20:19 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     rui.zhang@...el.com, amit.kucheria@...durent.com,
        linux-pm@...r.kernel.org, amit.kachhap@...il.com,
        daniel.lezcano@...aro.org, viresh.kumar@...aro.org,
        len.brown@...el.com, pavel@....cz, mhiramat@...nel.org,
        qyousef@...alina.io, wvw@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 00/23] Introduce runtime modifiable Energy Model



On 12/13/23 11:45, Rafael J. Wysocki wrote:
> On Wed, Dec 13, 2023 at 12:34 PM Dietmar Eggemann
> <dietmar.eggemann@....com> wrote:
>>
>> On 13/12/2023 10:23, Lukasz Luba wrote:
>>> Hi Dietmar,
>>>
>>> Thank you for the review, I will go one-by-one to respond
>>> your comments in patches as well. First comments are below.
>>>
>>> On 12/12/23 18:48, Dietmar Eggemann wrote:
>>>> On 29/11/2023 12:08, Lukasz Luba wrote:
>>
>> [...]
>>
>>>>> Changelog:
>>>>> v5:
>>>>> - removed 2 tables design
>>>>> - have only one table (runtime_table) used also in thermal (Wei, Rafael)
>>>>
>>>> Until v4 you had 2 EM's, the static and the modifiable (runtime). Now in
>>>> v5 this changed to only have one, the modifiable. IMHO it would be
>>>> better to change the existing table to be modifiable rather than staring
>>>> with two EM's and then removing the static one. I assume you end up with
>>>> way less code changes and the patch-set will become easier to digest for
>>>> reviewers.
>>>
>>> The patches are structured in this way following Daniel's recommendation
>>> I got when I was adding similar big changes to EM in 2020 (support all
>>> devices in kernel). The approach is as follows:
>>> 0. Do some basic clean-up/refactoring if needed for a new feature, to
>>>     re-use some code if possible in future
>>> 1. Introduce new feature next to the existing one
>>> 2. Add API and all needed infrastructure (structures, fields) for
>>>     drivers
>>> 3. Re-wire the existing drivers/frameworks to the new feature via new
>>>     API; ideally keep 1 patch per driver so the maintainer can easily
>>>     grasp the changes and ACK it, because it will go via different tree
>>>     (Rafael's tree); in case of some code clash in the driver's code
>>>     during merge - it will be a single driver so easier to handle
>>> 4. when all drivers and frameworks are wired up with the new feature
>>>     remove the old feature (structures, fields, APIs, etc)
>>> 5. Update the documentation with new latest state of desing
>>>
>>> In this approach the patches are less convoluted. Because if I remove
>>> the old feature and add new in a single patch (e.g. the main structure)
>>> that patch will have to modify all drivers to still compile. It
>>> would be a big messy patch for this re-design.
>>>
>>> I can see in some later comment from Rafael that he is OK with current
>>> patch set structure.
>>
>> OK, in case Rafael and Daniel prefer this, then it's fine.
>>
>> I just find it weird that we now have
>>
>> 70 struct em_perf_domain {
>> 71         struct em_perf_table __rcu *runtime_table;
>>                                         ^^^^^^^^^^^^^
>>
>> as the only EM table.
> 
> I agree that it would be better to call it something like em_table.
> 

OK, I'll change that. Thanks Rafael and Dietmar!