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    SubjectRe: [PATCH] [CPU-HOTPLUG] convert cpucontrol to be a rwsem
    On Mon, 1 Nov 2004, Dominik Brodowski wrote:

    > [CPU-HOTPLUG] Use a rw-semaphore for serializing and locking
    > Currently, lock_cpu_hotplug serializes multiple calls to cpufreq->target()
    > on multiple CPUs even though that's unneccessary. Even further, it
    > serializes these calls with totally unrelated other parts of the kernel...
    > some ppc64 event reporting, some cache management, and so on. In my opinion
    > locking should be done subsystem (and normally data-)specific, and disabling
    > CPU hotplug should just do that.
    > This patch converts the semaphore cpucontrol to be a rwsem which allows us
    > to use it for _both_ variants: locking (write) and (multiple) other parts
    > disabling CPU hotplug (read).
    > Only problem I see with this approach is that lock_cpu_hotplug_interruptible()
    > needs to disappear as there is no down_write_interruptible() for rw-semaphores.
    > Signed-off-by: Dominik Brodowski <>

    Agreed it makes a lot more sense, i think there could be some places where
    we use preempt_disable to protect against cpu offline which could
    converted, but that can come later.


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