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    Subject[RFC PATCH 0/5] Refcount based Cpu Hotplug. V2
    Hello everyone,

    This is the version 2 of the refcount based cpu-hotplug "locking"
    implementation.

    It incorporates the review comments from the first posting which
    can be found here --> http://lkml.org/lkml/2007/10/16/118.

    Changes since v1:
    - !CONFIG_HOTPLUG_CPU part is now handled correctly, thanks
    to the patch from Paul Jackson.

    - The cpu_hotplug_begin() uses a waitqueue instead of a completion struct
    where a writer can wait while there are active readers in the system.

    - Provided a new API's cpu_maps_update_begin(), cpu_maps_update_done()
    for serializing the updates to cpu_present_map and cpu_online_map.
    Thus threads which update the cpu_present_map should now call
    cpu_maps_update_begin instead of lock_cpu_hotplug(), since they play the
    role of writers.

    - pseries_processor_add() , pseries_processor_remove() now use
    cpu_maps_update_begin()/cpu_maps_update_done() in place of
    lock_cpu_hotplug()/unlock_cpu_hotplug().

    - Replaced the workqueue_mutex with workqueue_lock, which is a spinlock
    and guards the workqueues list.

    - Updated Documentation/cpu-hotplug.txt to reflect get_online_cpus(),
    put_online_cpus() in place of the old lock_cpu_hotplug(),
    unlock_cpu_hotplug().

    I'm Cc'ing the different subsystem maintainers who might be affected
    by the changes in the patchstack. Especially if they rely on
    lock_cpu_hotplug() to provide them protection for their local data
    structures as well.

    The patchstack which is based against 2.6.23-mm1 has behaved well
    when it was stress tested with kernbench running while continuously
    performing cpu-hotplug operations on i386, x86_64 and ppc64.

    Awaiting your feedback.

    Thanks and Regards
    gautham.
    --
    Gautham R Shenoy
    Linux Technology Center
    IBM India.
    "Freedom comes with a price tag of responsibility, which is still a bargain,
    because Freedom is priceless!"
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