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    SubjectRe: CONFIG_PREEMPT and server workloads
    On Thu, Mar 18, 2004 at 10:20:23AM -0500, Tom Sightler wrote:
    > Well, I reported an issue on my laptop several weeks ago where network
    > activity via my aironet wireless adapter would use 60-70% of the CPU but
    > only when PREEMPT was enabled. Looking back over the list I see other

    sounds like a preempt bug triggering in a softirq, or maybe an SMP bug
    triggering in UP.

    I certainly agree with Andrew that preempt cannot cause a 60/70%
    slowdown with a network card at least (if you do nothing but spinlocking
    in a loop then it's possible a 60/70% slowdown instead but the system
    time that a wifi card should take is nothing compared to the idle/user

    > I'll try to reproduce my issue with current generation kernels (last I
    > tested with PREEMPT was 2.6.1) and see if my problem is still there.
    > When I reported the issue last time no one seemed interested so I just
    > learned to disable preempt.

    This is fine IMHO (even if they are preempt bugs). Except if your
    machine is UP, if it's UP it would be better track down the bug, since
    it may still happen on a SMP box (I wouldn't be too surprised if wifi
    drivers aren't smp safe). I certainly agree with Andrew when he says
    preempt is a good debugging knob to debug smp bugs in UP (though I would
    leave it off in production UP, like in production SMP).
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