Re: 2.6.4-mm2
From: Nick Piggin
Date: Fri Mar 19 2004 - 23:31:04 EST
Andrew Morton wrote:
Nick Piggin <piggin@xxxxxxxxxxxxxxx> 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'?
Shouldnt.
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.
If you are measuring the same period of time, yes. If you
are measuring the same amount of work, no. I assumed the
latter. Maybe I'm wrong.
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?
I can't remember how much CPU reaim uses, I thought it was
quite a lot (ie. not IO bound).
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