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    SubjectRe: [discussion]sched: a rough proposal to enable power saving in scheduler
    On 08/15/2012 10:43 AM, Arjan van de Ven wrote:

    > The easy cop-out is provide the sysadmin a slider.
    > The slightly less easy one is to (and we're taking this approach
    > in the new P state code we're working on) say "in the default
    > setting, we're going to sacrifice up to 5% performance from peak
    > to give you the best power savings within that performance loss budget"
    > (with a slider that can give you 0%, 2 1/2% 5% and 10%)

    On a related note, I am looking at the c-state menu governor.

    We seem to have issues there, with Linux often going into a much
    deeper C state than warranted, which can lead to a fairly steep
    performance penalty for some workloads.

    One of the issues we identified is that detect_repeating_patterns
    would deal quite poorly with patterns that have a short pause,
    followed by a long pause, followed by another short pause. For
    example, pinging a virtual machine :)

    The idea Matthew and I have is simply planning for a shorter
    sleep period (discarding the outliers to the high end in the
    function once known as detect_repeating_patterns), and going
    to a deeper C state if we have significantly overslept.

    The new estimation code is easy, but for the past days I have
    been looking through the timer code to figure out how such a
    timer could fire, and how we could recognize it without it
    looking like a normal wakeup, if we do not end up accidentally
    waking up another CPU, etc...

    I guess I should probably post what I have and kick off a
    debate between people who know that code much better than I do :)

    All rights reversed

     \ /
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