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Date:   Tue, 6 Mar 2018 19:56:14 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Patrick Bellasi <patrick.bellasi@arm.com>
Cc:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Paul Turner <pjt@google.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Todd Kjos <tkjos@android.com>,
        Joel Fernandes <joelaf@google.com>,
        Steve Muckle <smuckle@google.com>
Subject: Re: [PATCH v5 1/4] sched/fair: add util_est on top of PELT
Message-ID: <20180306185614.GF25201@hirez.programming.kicks-ass.net>
References: <20180222170153.673-1-patrick.bellasi@arm.com>
 <20180222170153.673-2-patrick.bellasi@arm.com>
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On Thu, Feb 22, 2018 at 05:01:50PM +0000, Patrick Bellasi wrote:
> +/**
> + * Estimation Utilization for FAIR tasks.
> + *
> + * Support data structure to track an Exponential Weighted Moving Average
> + * (EWMA) of a FAIR task's utilization. New samples are added to the moving
> + * average each time a task completes an activation. Sample's weight is
> + * chosen so that the EWMA will be relatively insensitive to transient changes
> + * to the task's workload.
> + *
> + * @enqueued: instantaneous estimated utilization of a task/cpu
> + *      task: the task's util_avg at last task dequeue time
> + *    cfs_rq: the sum of util_est.enqueued for each RUNNABLE task on that CPU
> + *
> + *  Thus, the util_est.enqueued of a task represents the contribution on the
> + *  estimated utilization of the CPU where that task is currently enqueued.
> + *
> + * @ewma: the Exponential Weighted Moving Average (EWMA) utilization of a task
> + *  Only for tasks we track a moving average of the past instantaneous
> + *  estimated utilization. This allows to absorb sporadic drops in
> + *  utilization of an otherwise almost periodic task.
> + *
> + */

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