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    SubjectRe: Why Semaphore Hardware-Dependent?
    Date
    On Tuesday 29 August 2006 12:05, David Howells wrote:

    >Because i386 (and x86_64) can do better by using XADDL/XADDQ.

    x86-64 has always used the spinlock based version.

    > On i386, CMPXCHG also ties you to what registers you may use for what to some
    > extent.

    We've completely given up these kinds of micro optimization for spinlocks,
    which are 1000x as critical as rwsems. And nobody was able to benchmark
    a difference.

    It is very very likely nobody could benchmark a difference on rwsems either.

    While I'm sure it's an interesting intellectual exercise to do these
    advanced rwsems it would be better for everybody else to go for a single
    maintainable C implementation.

    -Andi
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