Messages in this thread | | | Date | Thu, 22 Dec 2005 19:10:35 +1100 | From | Nick Piggin <> | Subject | Re: [patch 0/8] mutex subsystem, ANNOUNCE |
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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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