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    SubjectRe: [rfc][patch] queued spinlocks (i386)
    On Fri, Mar 23, 2007 at 11:04:18AM +0100, Ingo Molnar wrote:
    >> isnt this patented by MS? (which might not worry you SuSE/Novell guys,
    >> but it might be a worry for the rest of the world ;-)

    On Fri, Mar 23, 2007 at 11:32:44AM +0100, Nick Piggin wrote:
    > Hmm, it looks like they have implemented a system where the spinning
    > cpu sleeps on a per-CPU variable rather than the lock itself, and
    > the releasing cpu writes to that variable to wake it. They do this
    > so that spinners don't continually perform exclusive->shared
    > transitions on the lock cacheline. They call these things queued
    > spinlocks. They don't seem to be very patent worthy either, but
    > maybe it is what you're thinking of?

    Those exclusive-to-shared transitions are among the cacheline transfers
    typically accounted to the algorithms in their complexity analyses.

    -- wli
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