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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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