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    SubjectRe: 2.6.4-mm2
    Nick Piggin <piggin@cyberone.com.au> wrote:
    >
    > >>>
    > >>Thanks, so it's the CPU scheduler changes. Is that machine hyperthreaded?
    > >>And do you have CONFIG_X86_HT enabled?
    > >>
    > >
    > >Yes and CONFIG_X86_HT is enabled but I have hyperthreading disabled with
    > >'acpi=off noht' (whichever one does it.)
    > >
    >
    >
    > The oprofile for the 01 kernel says
    > CPU: P4 / Xeon, speed 1497.76 MHz (estimated)
    > while the 02 kernel says
    > CPU: P4 / Xeon with 2 hyper-threads, speed 1497.57 MHz (estimated)
    > What's going on there?

    Does the sched-domains patch break `acpi=off' or `noht'?

    > Other than that, nothing in the kernel profile jumps out at me:
    > schedule, __copy_from_user_ll and __copy_to_user_ll are all
    > significantly lower *after* the CPU scheduler changes, which
    > is an indicator that cache behaviour is better.

    No, it indicates that the kernel is getting less work done.

    > Sar says average context switches/second were 9064 and 6567 before
    > and after.
    >
    > The only thing I can see is the CPU utilisation averages show the
    > scheduler patches have more of a tendancy to load up one CPU more
    > before moving to another. This actually should be good behaviour,
    > generally but I wonder if it is hurting at all. I would be really
    > surprised if it was that significant.

    This machine is I/O-bound, the CPUs are mostly idle. It would appear to be
    some interaction between the I/O system and the CPU scheduler. Haven't we
    seen that with reaim also?

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