linux-kernel - Re: [PATCH v5 04/23] PM: EM: Refactor em_pd_get_efficient

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Date: Tue, 19 Dec 2023 10:58:17 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: rui.zhang@...el.com, amit.kucheria@...durent.com, rafael@...nel.org,
 linux-kernel@...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-pm@...r.kernel.org
Subject: Re: [PATCH v5 04/23] PM: EM: Refactor em_pd_get_efficient_state() to
 be more flexible



On 12/12/23 18:49, Dietmar Eggemann wrote:
> On 29/11/2023 12:08, Lukasz Luba wrote:
>> The Energy Model (EM) is going to support runtime modification. There
>> are going to be 2 EM tables which store information. This patch aims
>> to prepare the code to be generic and use one of the tables. The function
>> will no longer get a pointer to 'struct em_perf_domain' (the EM) but
>> instead a pointer to 'struct em_perf_state' (which is one of the EM's
>> tables).
> I thought the 2 EM tables design is gone?
> 
> IMHO it would be less code changes and hence a more enjoyable review
> experience if you would add the 'modifiable' feature to the existing EM
> (1) and not add (2) and then remove (1) in [21/23].

I have explained that to some other your email: such approach would
create a patch monster, touching all drivers and frameworks, to just
make sure they still can compile. This is not the right approach.


> 
> 
>   struct em_perf_domain {
> -	struct em_perf_state *table;                <-- (1)
>   	struct em_perf_table __rcu *runtime_table;  <-- (2)
> 
>> Prepare em_pd_get_efficient_state() for the upcoming changes and
>> make it possible to re-use. Return an index for the best performance
> 
> s/make it possible to re-use/make it possible to be re-used ?

OK

> 
>> state for a given EM table. The function arguments that are introduced
>> should allow to work on different performance state arrays. The caller of
>> em_pd_get_efficient_state() should be able to use the index either
>> on the default or the modifiable EM table.
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>> Reviewed-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>> ---
>>   include/linux/energy_model.h | 30 +++++++++++++++++-------------
>>   1 file changed, 17 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
>> index b9caa01dfac4..8069f526c9d8 100644
>> --- a/include/linux/energy_model.h
>> +++ b/include/linux/energy_model.h
>> @@ -175,33 +175,35 @@ void em_dev_unregister_perf_domain(struct device *dev);
>>   
>>   /**
>>    * em_pd_get_efficient_state() - Get an efficient performance state from the EM
>> - * @pd   : Performance domain for which we want an efficient frequency
>> - * @freq : Frequency to map with the EM
>> + * @state:		List of performance states, in ascending order
> 
> (3)
> 
>> + * @nr_perf_states:	Number of performance states
>> + * @freq:		Frequency to map with the EM
>> + * @pd_flags:		Performance Domain flags
>>    *
>>    * It is called from the scheduler code quite frequently and as a consequence
>>    * doesn't implement any check.
>>    *
>> - * Return: An efficient performance state, high enough to meet @freq
>> + * Return: An efficient performance state id, high enough to meet @freq
>>    * requirement.
>>    */
>> -static inline
>> -struct em_perf_state *em_pd_get_efficient_state(struct em_perf_domain *pd,
>> -						unsigned long freq)
>> +static inline int
>> +em_pd_get_efficient_state(struct em_perf_state *table, int nr_perf_states,
>> +			  unsigned long freq, unsigned long pd_flags)
> 
> (3) but em_pd_get_efficient_state(struct em_perf_state *table
>                                                          ^^^^^
> [...]

Good catch, I'll change that.