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    SubjectRe: [PATCH] Yielding processor resources during lock contention
    Zwane Mwaikambo wrote:
    > On Sat, 11 Sep 2004, Andrew Morton wrote:

    >>Now, maybe Paul has tied himself into sufficiently tangly locking knots
    >>that in some circumstances he needs to spin on the lock and cannot schedule
    >>away. But he can still use a semaphore and spin on down_trylock.
    >>
    >>Confused by all of this.
    >
    >
    > Well currently it just enables preempt and spins like a mad man until the
    > lock is free. The idea is to allow preempt to get some scheduling done
    > during the spin.. But! if you accept this patch today, you get the
    > i386 version which will allow your processor to halt until a write to the
    > lock occurs whilst allowing interrupts to also trigger the preempt
    > scheduling, much easier on the caches.
    >

    That's the idea though isn't it? If your locks are significantly more
    expensive than a context switch and associated cache trashing, use a
    semaphore, hypervisor or no.

    I presume the hypervisor switch much incur the same sorts of costs as
    a context switch?
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