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    Subject[RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug
    Hello Everybody,

    This is an experiment towards process_freezer based implementation
    of cpu-hotplug. This is mainly based on ideas of Andrew Morton,
    Ingo Molnar and Paul Mckenney featured in the discussion

    This is an absolute bare-minimal implementation to check the feasibility
    of using process freezer for cpu-hotplug.

    The patchset comprises of four patches.
    o PATCH 1/4: Core implementation of freezer-based-hotplug.
    o PATCH 2/4: Revert changes to workqueue to make it work with the
    o PATCH 3/4: Eliminate hotcpu subsystem mutexes from sched and slab.
    o PATCH 4/4: Eliminate lock_cpu_hotplug from the kernel.

    These patches have been stress tested on i386 SMP box, with cpu-hotplug
    operations in a tight-loop and make -jN (kernel compile) running
    parallely. The cpu hotplug operations have been pretty stable.

    Certain threads like ksoftirqd/1, firmware.agent
    were not frozen during the hotplug operations. However, these
    were rare occurances.

    This implementation is by no means perfect or complete. Things
    that are yet to be done are as follows:

    - Most of Paul's suggestions including introduction of new states
    for process freezer like PFE_SUSPEND, PFE_KPROBES, PFE_HOTPLUG
    so that processes which are not concerned with these events
    can be exempted from being frozen.

    - Ensure the working of cpu_hotplug on all architectures on which
    it is supported. At present, it has been tested only on i386.

    - Updated documentation for cpu-hotplug.

    Any feedback would be greatly appreciated.

    Thanks and Regards
    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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