linux-kernel - Re: [PATCH v2 03/17] PM: EM: Refactor em_pd_get_efficient

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Message-ID: <418bef75-883c-2442-3376-03fd7537c734@arm.com>
Date:   Tue, 30 May 2023 13:06:14 +0200
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,
        Pierre.Gondois@....com, ionela.voinescu@....com,
        rostedt@...dmis.org, mhiramat@...nel.org
Subject: Re: [PATCH v2 03/17] PM: EM: Refactor em_pd_get_efficient_state() to
 be more flexible

On 12/05/2023 11:57, Lukasz Luba wrote:
> Prepare em_pd_get_efficient_state() for the upcoming changes and
> make it possible to re-use. Return an index for the best performance

Don't get the `possible to re-use`? Did you mean `possible to be
re-used`? But then `re-used` for what?

> state. 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.

This describes the WHAT but not the WHY.

> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> ---
>  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
> + * @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)
>  {
>  	struct em_perf_state *ps;
>  	int i;
>  
> -	for (i = 0; i < pd->nr_perf_states; i++) {
> -		ps = &pd->table[i];
> +	for (i = 0; i < nr_perf_states; i++) {
> +		ps = &table[i];
>  		if (ps->frequency >= freq) {
> -			if (pd->flags & EM_PERF_DOMAIN_SKIP_INEFFICIENCIES &&
> +			if (pd_flags & EM_PERF_DOMAIN_SKIP_INEFFICIENCIES &&
>  			    ps->flags & EM_PERF_STATE_INEFFICIENT)
>  				continue;
> -			break;
> +			return i;
>  		}
>  	}
>  
> -	return ps;
> +	return nr_perf_states - 1;
>  }
>  
>  /**
> @@ -226,7 +228,7 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>  {
>  	unsigned long freq, scale_cpu;
>  	struct em_perf_state *ps;
> -	int cpu;
> +	int cpu, i;
>  
>  	if (!sum_util)
>  		return 0;
> @@ -251,7 +253,9 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
>  	 * Find the lowest performance state of the Energy Model above the
>  	 * requested frequency.
>  	 */
> -	ps = em_pd_get_efficient_state(pd, freq);
> +	i = em_pd_get_efficient_state(pd->table, pd->nr_perf_states, freq,
> +				      pd->flags);
> +	ps = &pd->table[i];
>  
>  	/*
>  	 * The capacity of a CPU in the domain at the performance state (ps)