linux-kernel - Re: [RFC PATCH v3 4/6] sched/cpufreq: Introduce sugov_cpu_ramp

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Message-ID: <20191014143321.GH2328@hirez.programming.kicks-ass.net>
Date:   Mon, 14 Oct 2019 16:33:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Douglas RAILLARD <douglas.raillard@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        mingo@...hat.com, rjw@...ysocki.net, viresh.kumar@...aro.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, qperret@...rret.net,
        patrick.bellasi@...bug.net, dh.han@...sung.com
Subject: Re: [RFC PATCH v3 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost

On Fri, Oct 11, 2019 at 02:44:58PM +0100, Douglas RAILLARD wrote:
> Use the utilization signals dynamic to detect when the utilization of a
> set of tasks starts increasing because of a change in tasks' behavior.
> This allows detecting when spending extra power for faster frequency
> ramp up response would be beneficial to the reactivity of the system.
> 
> This ramp boost is computed as the difference
> util_avg-util_est_enqueued. This number somehow represents a lower bound

That reads funny, maybe 'as the difference between util_avg and
util_est_enqueued' ?

> of how much extra utilization this tasks is actually using, compared to
> our best current stable knowledge of it (which is util_est_enqueued).
> 
> When the set of runnable tasks changes, the boost is disabled as the
> impact of blocked utilization on util_avg will make the delta with
> util_est_enqueued not very informative.

> @@ -561,6 +604,7 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
>  		}
>  	}
>  
> +
>  	return get_next_freq(sg_policy, util, max);
>  }

Surely we can do without this extra whitespace? :-)