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    SubjectRe: [PATCH RFC 1/2] sched: Minimize the idle cpu selection race window.
    On Tue, Oct 31, 2017 at 12:27:41AM -0500, Atish Patra wrote:
    > Currently, multiple tasks can wakeup on same cpu from
    > select_idle_sibiling() path in case they wakeup simulatenously
    > and last ran on the same llc. This happens because an idle cpu
    > is not updated until idle task is scheduled out. Any task waking
    > during that period may potentially select that cpu for a wakeup
    > candidate.
    >
    > Introduce a per cpu variable that is set as soon as a cpu is
    > selected for wakeup for any task. This prevents from other tasks
    > to select the same cpu again. Note: This does not close the race
    > window but minimizes it to accessing the per-cpu variable. If two
    > wakee tasks access the per cpu variable at the same time, they may
    > select the same cpu again. But it minimizes the race window
    > considerably.

    The very most important question; does it actually help? What
    benchmarks, give what numbers?

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