linux-kernel - Re: [PATCH v6 08/16] sched/cpufreq: uclamp: Add utilization clamping for FAIR tasks

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Message-ID: <20190122152132.GR27931@hirez.programming.kicks-ass.net>
Date:   Tue, 22 Jan 2019 16:21:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-api@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v6 08/16] sched/cpufreq: uclamp: Add utilization clamping
 for FAIR tasks

On Tue, Jan 15, 2019 at 10:15:05AM +0000, Patrick Bellasi wrote:
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -218,8 +218,15 @@ unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
>  	 * CFS tasks and we use the same metric to track the effective
>  	 * utilization (PELT windows are synchronized) we can directly add them
>  	 * to obtain the CPU's actual utilization.
> +	 *
> +	 * CFS utilization can be boosted or capped, depending on utilization
> +	 * clamp constraints requested by currently RUNNABLE tasks.
> +	 * When there are no CFS RUNNABLE tasks, clamps are released and
> +	 * frequency will be gracefully reduced with the utilization decay.
>  	 */
> -	util = util_cfs;
> +	util = (type == ENERGY_UTIL)
> +		? util_cfs
> +		: uclamp_util(rq, util_cfs);

That's pretty horrible; what's wrong with:

	util = util_cfs;
	if (type == FREQUENCY_UTIL)
		util = uclamp_util(rq, util);

That should generate the same code, but is (IMO) far easier to read.

>  	util += cpu_util_rt(rq);
>  
>  	dl_util = cpu_util_dl(rq);