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    SubjectRe: [PATCH v4 14/16] locking/rwsem: Guard against making count negative
    On Fri, Apr 19, 2019 at 02:02:07PM +0200, Peter Zijlstra wrote:
    > On Fri, Apr 19, 2019 at 12:26:47PM +0200, Peter Zijlstra wrote:
    > > I thought of a horrible horrible alternative:
    >
    > Hurm, that's broken as heck. Let me try again.

    So I can't make that scheme work, it all ends up wanting to have
    cmpxchg().

    Do we have a performance comparison somewhere of xadd vs cmpxchg
    readers? I tried looking in the old threads, but I can't seem to locate
    it.

    We need new instructions :/ Or more clever than I can muster just now.

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