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    SubjectRe: [patch] preemptive kernel, preemptive-2.3.52-A7
       Date: 	Sat, 25 Mar 2000 23:24:59 -0700

    The hidden assumption of the pre-emption patch is that there are kernel
    paths that take more than 500us to reach a schedule or return to user
    mode. Obviously there are such paths, but what are they and why can't they
    be fixed?

    Just to name a few obvious ones:

    1) write(fd, buffer, SOME_LARGE_VALUE);
    2) read(fd, buffer, SOME_LARGE_VALUE);

    I honestly can't think of a way in which we'd want to deal with these
    cases, except to perhaps check need_resched after or before copying
    each page into/out-of the page cache out-of/into user space. And I
    believe this is what the pre-emption patch and Ingo's low-latency
    variant is up to basically.

    David S. Miller

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