linux-kernel - Re: [PATCH v4 07/18] PM: EM: Refactor struct em_perf_domain and add default

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Message-ID: <7e2e64d7-4b10-8d58-03c9-e5a5129f864e@arm.com>
Date:   Fri, 29 Sep 2023 09:45:03 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        dietmar.eggemann@....com, 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, mhiramat@...nel.org,
        qyousef@...alina.io, wvw@...gle.com
Subject: Re: [PATCH v4 07/18] PM: EM: Refactor struct em_perf_domain and add
 default_table



On 9/26/23 19:52, Rafael J. Wysocki wrote:
> On Mon, Sep 25, 2023 at 10:11 AM Lukasz Luba <lukasz.luba@....com> wrote:
>>
>> The Energy Model is going to support runtime modifications. Refactor old
>> implementation which accessed struct em_perf_state and introduce
>> em_perf_domain::default_table to clean up the design. This new field
>> will help to better distinguish 2 performance state tables.
>>
>> Update all drivers or frameworks which used the old field:
>> em_perf_domain::table and now should use em_perf_domain::default_table.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>

[snip]

>> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
>> index 8069f526c9d8..d236e08e80dc 100644
>> --- a/include/linux/energy_model.h
>> +++ b/include/linux/energy_model.h
>> @@ -36,9 +36,19 @@ struct em_perf_state {
>>    */
>>   #define EM_PERF_STATE_INEFFICIENT BIT(0)
>>
>> +/**
>> + * struct em_perf_table - Performance states table
>> + * @state:     List of performance states, in ascending order
>> + * @rcu:       RCU used for safe access and destruction
>> + */
>> +struct em_perf_table {
>> +       struct em_perf_state *state;
>> +       struct rcu_head rcu;
> 
> There is no explanation of the role of this rcu_head in the changelog
> or anywhere in this patch.
> 
> It is also not used as of this patch AFAICS.
> 
> It would be better to add it when it actually gets used IMV.

That's a good point. I will introduce this 'rcu' field later.