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    SubjectRe: [patch 0/8] mutex subsystem, ANNOUNCE
    Arjan van de Ven wrote:
    > On Thu, 2005-12-22 at 18:56 +1100, Nick Piggin wrote:
    >
    >>Ingo Molnar wrote:
    >>
    >>>* Nick Piggin <nickpiggin@yahoo.com.au> wrote:
    >>>
    >>>
    >>>
    >>>>It would be nice to first do a run with a fair implementation of
    >>>>mutexes.
    >>>
    >>>
    >>>which fairness implementation do you mean - the one where all tasks will
    >>>get the lock in fair FIFO order, and a 'lucky bastard' cannot steal the
    >>>lock from waiters and thus put them at an indefinite disadvantage?
    >>>
    >>
    >>I guess so. I'm not so worried about the rare 'lucky bastard' ie. a
    >>lock request coming in concurrently, but rather the naturally favoured
    >>'this CPU' taking the lock again after waking up the head waiter but
    >>before it gets a chance to run / transfer the cacheline.
    >
    >
    > that's just the most evil lucky bastard....
    >

    I'd probably just call "bastard": it is probably _unlucky_ when _doesn't_
    get to retake the lock, judging by the factor-of-4 speedup that Jes
    demonstrated.

    Which might be the right thing to do, but having the front waiter go to
    the back of the queue I think is not.

    --
    SUSE Labs, Novell Inc.

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