linux-kernel - Re: [RFC PATCH v4 3/6] sched/cpufreq: Hook em_pd_get_higher_power() into get_next

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Message-ID: <20200123161644.GA144523@google.com>
Date:   Thu, 23 Jan 2020 16:16:44 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Douglas RAILLARD <douglas.raillard@....com>
Cc:     linux-kernel@...r.kernel.org, rjw@...ysocki.net,
        viresh.kumar@...aro.org, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH v4 3/6] sched/cpufreq: Hook em_pd_get_higher_power()
 into get_next_freq()

On Wednesday 22 Jan 2020 at 17:35:35 (+0000), Douglas RAILLARD wrote:
> @@ -210,9 +211,16 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
>  	struct cpufreq_policy *policy = sg_policy->policy;
>  	unsigned int freq = arch_scale_freq_invariant() ?
>  				policy->cpuinfo.max_freq : policy->cur;
> +	struct em_perf_domain *pd = sugov_policy_get_pd(sg_policy);
>  
>  	freq = map_util_freq(util, freq, max);
>  
> +	/*
> +	 * Try to get a higher frequency if one is available, given the extra
> +	 * power we are ready to spend.
> +	 */
> +	freq = em_pd_get_higher_freq(pd, freq, 0);

I find it sad that the call just below to cpufreq_driver_resolve_freq()
and cpufreq_frequency_table_target() iterates the OPPs all over again.
It's especially a shame since most existing users of the EM stuff do
have a cpufreq frequency table.

Have you looked at hooking this inside cpufreq_driver_resolve_freq()
instead ? If we have a well-formed EM available, the call to
cpufreq_frequency_table_target() feels redundant, so we might want to
skip it.

Thoughts ?

Quentin