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SubjectRe: 2.6.4-mm2
Nick Piggin <> 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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