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    SubjectRe: pipe and af/unix latency differences between aa and jam on smp
    On Mon, 8 Jul 2002 wrote:

    > Sometimes small differences in LMbench between -jam and -aa are
    > just CPU bounces on SMP. The difference for pipe and af/unix latency
    > only appears on SMP too, but it is very consistent. (My k6/2
    > has small differences between -aa and -jam for pipe and af/unix
    > latency).
    > You will know better what could make the difference:
    > This is the averages:
    > *Local* Communication latencies in microseconds - smaller is better
    > -------------------------------------------------------------------
    > kernel Pipe AF/Unix
    > ----------------- ------- -------
    > 2.4.19-pre10-aa4 33.941 70.216
    > 2.4.19-pre10-jam2 7.877 16.699

    Small differences? The only thing I would call small is the latency of the
    jam kernel!

    If (a) this is a real value which results in ~5x latency reduction in
    non-benchmark applications, and (b) doesn't have some resulting penalty
    (there are some free lunches in Linux), then it would be desirable.

    I have an IPC test which measures time for a datum to move form process A
    to process B and back, using various methods, I'll try to build these
    kernels and test it in my next free day. I'd love to test latency of SysV
    message queues as well, since these turn out to be good solutions to some
    types of N:M client-server problems.

    bill davidsen <>
    CTO, TMR Associates, Inc
    Doing interesting things with little computers since 1979.

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