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    SubjectRe: [RFC PATCH v1 00/11] Create fast idle path for short idle periods
    On Mon, Jul 10, 2017 at 06:42:06PM +0200, Peter Zijlstra wrote:
    > On Mon, Jul 10, 2017 at 07:46:09AM -0700, Andi Kleen wrote:
    > > > So how much of the gain is simply due to skipping NOHZ? Mike used to
    > > > carry a patch that would throttle NOHZ. And that is a _far_ smaller and
    > > > simpler patch to do.
    > >
    > > Have you ever looked at a ftrace or PT trace of the idle entry?
    > >
    > > There's just too much stuff going on there. NOHZ is just the tip
    > > of the iceberg.
    >
    > I have, and last time I did the actual poking at the LAPIC (to make NOHZ
    > happen) was by far the slowest thing happening.

    That must have been a long time ago because modern systems use TSC deadline
    for a very long time ...

    It's still slow, but not as slow as the LAPIC.

    > Data to indicate what hurts how much would be a very good addition to
    > the Changelogs. Clearly you have some, you really should have shared.

    Aubrey?

    -Andi

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