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    SubjectRe: [rfc][patch] queued spinlocks (i386)
    On Wed, Mar 28, 2007 at 12:26:57PM -0700, Davide Libenzi wrote:
    > On Wed, 28 Mar 2007, Nick Piggin wrote:
    >
    > > On Sat, Mar 24, 2007 at 06:29:59PM +0100, Ingo Molnar wrote:
    > > >
    > > > * Nikita Danilov <nikita@clusterfs.com> wrote:
    > > >
    > > > > Indeed, this technique is very well known. E.g.,
    > > > > http://citeseer.ist.psu.edu/anderson01sharedmemory.html has a whole
    > > > > section (3. Local-spin Algorithms) on them, citing papers from the
    > > > > 1990 onward.
    > > >
    > > > that is a cool reference! So i'd suggest to do (redo?) the patch based
    > > > on those concepts and that terminology and not use 'queued spinlocks'
    > > > that are commonly associated with MS's stuff. And as a result the
    > > > contended case would be optimized some more via local-spin algorithms.
    > > > (which is not a key thing for us, but which would be nice to have
    > > > nevertheless)
    > >
    > > Firstly, the terminology in that paper _is_ "queue lock", which isn't
    > > really surprising. I don't really know or care about what MS calls their
    > > locks, but I'd suggest that their queued spinlock is probably named in
    > > reference to its queueing property rather than its local spin property.
    >
    > The method you propose is otherwise called "Ticket Lock":
    >
    > http://en.wikipedia.org/wiki/Ticket_lock
    > http://www.cs.rochester.edu/research/synchronization/pseudocode/ss.html#ticket

    Yes, a ticket based FIFO queue isn't new... I think we have a lot of
    xamples already in the kernel. Using them to implement queue locks
    obviously isn't new either.

    I don't think we'd have to worry about patents.
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