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    SubjectRe: [patch 04/15] Generic Mutex Subsystem, add-atomic-call-func-x86_64.patch
    On Tue, Dec 20, 2005 at 11:35:22AM -0500, Nicolas Pitre wrote:
    > So 14 instructions total with preemption disabling, and that's with the
    > best implementation possible by open coding everything instead of
    > relying on generic functions/macros.

    I agree with your analysis Nicolas.

    However, don't forget to compare this with our existing semaphore
    implementation which is 9 instructions, or 8 for the SMP version.

    In total, this means that mutexes will be _FAR MORE EXPENSIVE_ on ARM
    than our semaphores.

    Forcing architectures down the "lets make everything generic" path
    does not always hack it. It can't do by its very nature. Generic
    implementations are *always* sub-optimal and it is pretty clear
    that any gain that mutexes _may_ give is completely wasted on ARM
    by the overhead of having a generic framework imposed upon us.

    So, to sum up, if this path is persued, mutexes will be a bloody
    disaster on ARM. We'd be far better off sticking to semaphores
    and ignoring this mutex stuff.

    Russell King
    Linux kernel 2.6 ARM Linux -
    maintainer of: 2.6 Serial core
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