signifanctly slowdown of FreeBSD 8.0-CURRENT/amd64

[bf]

>2009/5/30 Attilio Rao <attilio at freebsd.org>:
>> 2009/5/30 O. Hartmann <ohartman at mail.zedat.fu-berlin.de>:
>>> Attilio Rao wrote:
>>>> 2009/5/30 O. Hartmann <ohartman at mail.zedat.fu-berlin.de>:
>>>>
>>>>> Hello.
>>>>> I realized a significant slowdown of FreeBSD 8.0-CURRENT/amd64 on every
>>>>> box I run. I have the most recent FreeBSD 8.0-CURRENT/amd64 with custom
>>>>> kernel and switched off every debugging. I see a drastic slowdown
>>>>> whenever heavy I/O on UFS2 and ZFS partitions is performed and whenever
>>>>> some compilation is done (compiling world and kernel).

...

>Also, did you compile the single-core athlon64 without the option SMP?
>
>Thanks,
>Attilio

I'm running the r193133 amd64 with a custom kernel and all debugging off
on an AMD Athlon64 3400+ single-core, and I haven't noticed any significant
slowing, although I haven't been doing any systematic benchmarking.

What would be the penalties of running an SMP -CURRENT kernel on
single-core hardware with no hyperthreading? Can anyone quantify the
typical added overhead?  Or, counterintuitively, would an SMP kernel
be better in some ways?

Regards,
          b.