linux-kernel - Re: [PATCH v7 12/23] PM: EM: Add em_perf_state_from

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Date: Tue, 6 Feb 2024 13:55:13 +0000
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, mhiramat@...nel.org, qyousef@...alina.io, wvw@...gle.com,
 xuewen.yan94@...il.com, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org, rafael@...nel.org
Subject: Re: [PATCH v7 12/23] PM: EM: Add em_perf_state_from_pd() to get
 performance states table



On 1/29/24 18:13, Dietmar Eggemann wrote:
> On 17/01/2024 10:57, Lukasz Luba wrote:
> 
> [...]
> 
>> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
>> index 494df6942cf7..5ebe9dbec8e1 100644
>> --- a/include/linux/energy_model.h
>> +++ b/include/linux/energy_model.h
>> @@ -339,6 +339,23 @@ static inline int em_pd_nr_perf_states(struct em_perf_domain *pd)
>>   	return pd->nr_perf_states;
>>   }
>>   
>> +/**
>> + * em_perf_state_from_pd() - Get the performance states table of perf.
>> + *				domain
>> + * @pd		: performance domain for which this must be done
>> + *
>> + * To use this function the rcu_read_lock() should be hold. After the usage
>> + * of the performance states table is finished, the rcu_read_unlock() should
>> + * be called.
>> + *
>> + * Return: the pointer to performance states table of the performance domain
>> + */
>> +static inline
>> +struct em_perf_state *em_perf_state_from_pd(struct em_perf_domain *pd)
> 
> This is IMHO hard to get since:
> 
>    struct em_perf_table {
>      struct rcu_head rcu;
>      struct kref kref;
>      struct em_perf_state state[];
>    };
> 
> So very often a 'struct em_perf_table' is named 'table' and 'struct
> em_perf_table::state' as well. E.g. in em_adjust_new_capacity().
> 
>    struct em_perf_state *new_table;
> 
>    new_table = em_table->state;
> 
> In older EM code, we used 'struct em_perf_state *ps' to avoid this
> confusion, I guess.
> 
> And what you get from the PD is actually a state vector so maybe:
> 
> struct em_perf_state *em_get_perf_states(struct em_perf_domain *pd)
> 
> The 'from_pd' seems obvious because of the parameter?

Rafael proposed that function name in his review comments, so I
followed. I might address your comment about the:
'struct em_perf_state *ps'
while I will do re-basing and sending v8.