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    SubjectRe: Linux 2.4.19-rc3 (hyperthreading)
    Date
    I would caution against having hyperthreading on by default in the 2.4.19 
    release. I am seeing a significant degrade in network workloads on P4 with
    hyperthreading on. On 2.4.19-pre10, I get 788 Mbps on NetBench, but on
    2.4.19-rc1 (and probably rc3, should know in an hour), I get 690 Mbps. It is
    clearly a hyperthreading/interrupt routing issue. On this system (4 x P4),
    with no hyperthreading, there is enough CPU to handle all interrupts on CPU0
    (this is where all ints go by default). With hyperthreading on, I get "1/2"
    of a CPU for interrupt processing. What ends up happenning is that CPU0 is
    at 100%, while CPU1-CPU7 are at 75%. Now I know the "noth" is available, but
    since hyperthreading is not proven to give a performance boost to more than
    1/2 of the common workloads for linux users (or is it? who has done tests?),
    I'd like to see this default behavior reversed, and still use acpismp=force
    to enable hyperthreading.

    Also, If anyone has performance results for their workloads showing a boost
    with hyperthreading, I would really like to know.

    -Andrew Theurer



    <<So here goes rc3. Another -rc is going to come only in the case of really
    critical problem(s).

    I'm attaching the rc2->rc3 changelog only because the full changelog got
    too big (I guess thats why my -rc2 announce mail didnt go to lk).>>


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