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    SubjectRe: suspend blockers & Android integration
    On Fri, 4 Jun 2010, Ingo Molnar wrote:

    > Note that this does not necessarily have to be implemented as 'execute suspend
    > from the idle task' code: scheduling from the idle task, while can certainly
    > be made to work, is a somewhat recursive concept that we might want to avoid
    > for robustness reasons.
    > Instead, the 'deepest idle' (suspend) method could consist of a wakeup of a
    > kernel thread (or of any of the existing kernel threads such as the migration
    > thread) - which kernel thread then does a race-free suspend: it offlines all
    > but one CPU [on platforms that need that] and then initiates the suspend - but
    > aborts the attempt if there's any sign of wakeup activity.

    Out of morbid curiosity... A typical sign of wakeup activity is a
    thread becoming runnable because of expiration of a kernel timer or an
    I/O completion interrupt. How would the "race-free suspend" thread
    detect this sort of thing? Indeed, isn't the inability to detect these
    part of what makes the existing suspend implementation (the freezer in
    particular) not race-free?

    Alan Stern

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