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

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Date: Mon, 29 Jan 2024 19:13:12 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org, rafael@...nel.org
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
Subject: Re: [PATCH v7 12/23] PM: EM: Add em_perf_state_from_pd() to get
 performance states table

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?

[...]