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    SubjectRe: [PATCH 1/5] Add a global synchronization point for pvclock
    On 04/19/2010 02:19 PM, Peter Zijlstra wrote:
    >
    >> Still have two cmpxchgs in the common case. The first iteration will
    >> fail, fetching last_value, the second will work.
    >>
    >> It will be better when we have contention, though, so it's worthwhile.
    >>
    > Right, another option is to put the initial read outside of the loop,
    > that way you'll have the best of all cases, a single LOCK'ed op in the
    > loop, and only a single LOCK'ed op for the fast path on sensible
    > architectures ;-)
    >
    > last = atomic64_read(&last_value);
    > do {
    > if (ret< last)
    > return last;
    > last = atomic64_cmpxchg(&last_value, last, ret);
    > } while (unlikely(last != ret));
    >
    > Or so.
    >
    >

    Yes, looks optimal when !NONSTOP_TSC.

    --
    error compiling committee.c: too many arguments to function



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