linux-kernel - Re: [PATCH] PM / EM: Inefficient OPPs detection

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Message-ID: <YHg8s4VTQdiBNOpr@google.com>
Date:   Thu, 15 Apr 2021 13:16:35 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Vincent Donnefort <vincent.donnefort@....com>
Cc:     peterz@...radead.org, rjw@...ysocki.net, viresh.kumar@...aro.org,
        vincent.guittot@...aro.org, linux-kernel@...r.kernel.org,
        ionela.voinescu@....com, lukasz.luba@....com,
        dietmar.eggemann@....com
Subject: Re: [PATCH] PM / EM: Inefficient OPPs detection

On Thursday 08 Apr 2021 at 18:10:29 (+0100), Vincent Donnefort wrote:
> --- 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>
>  
> @@ -164,6 +165,9 @@ 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);

I remember this was discussed when Douglas sent his patches some time
ago, but I still find it sad we index the EM table here but still
re-index the cpufreq frequency table later :/

Yes in your case this lookup is very inexpensive, but still. EAS relies
on the EM's table matching cpufreq's accurately, so this second lookup
still feels rather unnecessary ...

>  	if (freq == sg_policy->cached_raw_freq && !sg_policy->need_freq_update)
>  		return sg_policy->next_freq;
>  
> -- 
> 2.7.4
>