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Date:   Fri, 29 Sep 2023 09:45:03 +0100
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Subject: Re: [PATCH v4 07/18] PM: EM: Refactor struct em_perf_domain and add
 default_table
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To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        dietmar.eggemann@arm.com, rui.zhang@intel.com,
        amit.kucheria@verdurent.com, amit.kachhap@gmail.com,
        daniel.lezcano@linaro.org, viresh.kumar@linaro.org,
        len.brown@intel.com, pavel@ucw.cz, mhiramat@kernel.org,
        qyousef@layalina.io, wvw@google.com
References: <20230925081139.1305766-1-lukasz.luba@arm.com>
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 <CAJZ5v0iYkVKuVULv9X7EKpC9feh8UPf8S2ZnY+X+1tyOYn0ing@mail.gmail.com>
From:   Lukasz Luba <lukasz.luba@arm.com>
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On 9/26/23 19:52, Rafael J. Wysocki wrote:
> On Mon, Sep 25, 2023 at 10:11 AM Lukasz Luba <lukasz.luba@arm.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@arm.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.