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    SubjectRe: [PATCH v5 09/14] sched: Add over-utilization/tipping point indicator
    On Tue, 24 Jul 2018 at 14:26, Quentin Perret <quentin.perret@arm.com> wrote:
    >
    > From: Morten Rasmussen <morten.rasmussen@arm.com>
    >
    > Energy-aware scheduling is only meant to be active while the system is
    > _not_ over-utilized. That is, there are spare cycles available to shift
    > tasks around based on their actual utilization to get a more
    > energy-efficient task distribution without depriving any tasks. When
    > above the tipping point task placement is done the traditional way based
    > on load_avg, spreading the tasks across as many cpus as possible based
    > on priority scaled load to preserve smp_nice. Below the tipping point we
    > want to use util_avg instead. We need to define a criteria for when we
    > make the switch.
    >
    > The util_avg for each cpu converges towards 100% (1024) regardless of

    remove the "(1024)" because util_avg converges to max cpu capacity
    which can be different from 1024

    > how many task additional task we may put on it. If we define
    > over-utilized as:
    >
    > sum_{cpus}(rq.cfs.avg.util_avg) + margin > sum_{cpus}(rq.capacity)
    >
    > some individual cpus may be over-utilized running multiple tasks even
    > when the above condition is false. That should be okay as long as we try
    > to spread the tasks out to avoid per-cpu over-utilization as much as
    > possible and if all tasks have the _same_ priority. If the latter isn't
    > true, we have to consider priority to preserve smp_nice.
    >

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