linux-kernel - Re: [PATCH v2 3/3] PM / EM: Skip inefficient OPPs

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Date:   Tue, 25 May 2021 10:48:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Donnefort <vincent.donnefort@....com>
Cc:     rjw@...ysocki.net, viresh.kumar@...aro.org,
        vincent.guittot@...aro.org, qperret@...gle.com,
        linux-kernel@...r.kernel.org, ionela.voinescu@....com,
        lukasz.luba@....com, dietmar.eggemann@....com
Subject: Re: [PATCH v2 3/3] PM / EM: Skip inefficient OPPs

On Fri, May 21, 2021 at 05:54:24PM +0100, Vincent Donnefort wrote:
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 4f09afd..5a91a2b 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -10,6 +10,7 @@
>  
>  #include "sched.h"
>  
> +#include <linux/energy_model.h>
>  #include <linux/sched/cpufreq.h>
>  #include <trace/events/power.h>
>  
> @@ -153,6 +154,9 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>  
>  	freq = map_util_freq(util, freq, max);
>  
> +	/* Avoid inefficient performance states */
> +	freq = em_pd_get_efficient_freq(em_cpu_get(policy->cpu), freq);
> +
>  	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
>  		return sg_policy->next_freq;
>  

This seems somewhat unfortunate, it adds a loop over the OPPs only to
then call into cpufreq to do the exact same thing again :/