linux-kernel - Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks

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Date:   Tue, 7 Aug 2018 15:26:30 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping
 for RT tasks

Hi,

On 06/08/18 17:39, Patrick Bellasi wrote:

[...]

> @@ -223,13 +224,25 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
>  	 * 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 configured for currently RUNNABLE tasks.
> +	 * CFS and RT utilizations can be boosted or capped, depending on
> +	 * utilization constraints enforce by currently RUNNABLE tasks.
> +	 * They are individually clamped to ensure fairness across classes,
> +	 * meaning that CFS always gets (if possible) the (minimum) required
> +	 * bandwidth on top of that required by higher priority classes.

Is this a stale comment written before UCLAMP_SCHED_CLASS was
introduced? It seems to apply to the below if branch only.

>  	 */
> -	util = cpu_util_cfs(rq);
> -	if (util)
> -		util = uclamp_util(cpu_of(rq), util);
> -	util += cpu_util_rt(rq);
> +	util_cfs = cpu_util_cfs(rq);
> +	util_rt  = cpu_util_rt(rq);
> +	if (sched_feat(UCLAMP_SCHED_CLASS)) {
> +		util = 0;
> +		if (util_cfs)
> +			util += uclamp_util(cpu_of(rq), util_cfs);
> +		if (util_rt)
> +			util += uclamp_util(cpu_of(rq), util_rt);
> +	} else {
> +		util  = cpu_util_cfs(rq);
> +		util += cpu_util_rt(rq);
> +		util  = uclamp_util(cpu_of(rq), util);
> +	}

Best,

- Juri