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    SubjectRe: [PATCH 0/4] MCS spinlocks: Cancellable MCS spinlock rework
    On Mon, Jul 07, 2014 at 11:50:15AM -0700, Jason Low wrote:
    > The main purpose of this patchset is to reduce the size of the
    > cancellable MCS spinlock and reduce the overhead of rwsem
    > (currently the largest lock in the kernel).
    >
    > The overhead of the cancellable MCS lock is a pointer to a per-cpu node
    > structure which requires 64 bits on 64 bit systems. Instead of a pointer
    > to the per-cpu node, we can instead store the CPU # corresponding to the
    > node in atomic_t. This reduces the overhead by 32 bits on 64 bit systems.
    >
    > This then opens the opportunity to reduce the size of the rw_semaphore
    > structure (one of the current users of this MCS lock) by moving around some
    > of its fields. Due to padding, we would reduce the size of that structure
    > by 64 bits (on 64 bit systems). This makes it more in line with the size
    > of the mutex structure.

    Dave Chinner was very interested in this..
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