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    SubjectRe: [PATCH 2/6] PM: Asynchronous resume of devices
    On Wed, 26 Aug 2009, Rafael J. Wysocki wrote:

    > From: Rafael J. Wysocki <rjw@sisk.pl>
    >
    > Theoretically, the total time of system sleep transitions (suspend
    > to RAM, hibernation) can be reduced by running suspend and resume
    > callbacks of device drivers in parallel with each other. However,
    > there are dependencies between devices such that, for example, we may
    > not be allowed to put one device into a low power state before
    > anohter one has been suspended (e.g. we cannot suspend a bridge
    > before suspending all devices behind it). In particular, we're not
    > allowed to suspend the parent of a device before suspending the
    > device itself. Analogously, we're not allowed to resume a device
    > before resuming its parent.

    > In this version of the patch the async threads started to execute
    > the resume callbacks of specific device don't exit immediately having
    > done that, but search dpm_list for devices whose PM dependencies have
    > already been satisfied and execute their callbacks without waiting.

    Given this design, why bother to invoke device_resume() for the async
    devices? Why not just start up a bunch of async threads, each of which
    calls async_resume() repeatedly until everything is finished? (And
    rearrange async_resume() to scan the list first and do the actual
    resume second.)

    The same goes for the noirq versions.

    Alan Stern



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