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    SubjectRe: low-latency patches
    On Sat, 2001-10-06 at 02:05, Bob McElrath wrote:
    > [...]
    > Correct me if I'm wrong, but the former uses spinlocks to know when it can
    > preempt the kernel, and the latter just tries to reduce latency by adding
    > (un)conditional_schedule and placing it at key places in the kernel?

    Correct. The low-latency patch does some other work to try to break up
    huge routines, too.

    > My questions are:
    > 1) Which of these two projects has better latency performance? Has anyone
    > benchmarked them against each other?

    I suspect you will find a lower average latency with the preemption
    patch. However, I suspect with the low-latency patch you may see a
    lower maximum since it works on some of the terribly long-held lock

    In truth, a combination of the two could prove useful. I have been
    working on finding the worst-case non-preemption regions (longest held
    lock regions) in the kernel.

    > 2) Will either of these ever be merged into Linus' kernel (2.5?)

    I hope :)

    > 3) Is there a possibility that either of these will make it to non-x86
    > platforms? (for me: alpha) The second patch looks like it would
    > straightforwardly work on any arch, but the for it is only in
    > arch/i386. Robert Love's patches would need some arch-specific asm...

    Andrew's patch should work fine on all platforms, although I think the
    configure statement is in the processor section so you will need to move
    it to arch/alpha/

    The preemption patch has a small amount of arch-independent code but we
    are working on supporting all architectures. 2.5...

    Robert Love

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