HT/SMP Question (FreeBSD 6.0)

Joerg Pernfuss elessar at
Fri Feb 17 07:51:06 PST 2006

On Fri, 17 Feb 2006 10:32:42 -0500
Dave Stephens <hsoftdev17 at> wrote:

> I've upgraded my web server's CPU to one with HT and I was curious
> about the current state of affairs with HT compatibility and speed
> under FreeBSD 6.0.  I've followed the SMP lists for some time and
> honestly I've lost track on whether it's a good thing to enable SMP in
> my kernel or not and whether there are special options for HT in the
> kernel config.
> Sorry this is so vague, I'm not having a problem as I'm running my
> custom kernel with HT/SMP disabled for now.  In my searches the
> consensus seems to be that if you don't have 2 real cores don't bother
> with SMP and I want to confirm that is still the case.  Any info
> anyone can offer would be greatly appreciated!  Thanks!

The best advice I can give you is that I can't give you advice.

Varous combinations of HT enabled/disabled and SCHED_4BSD/ULE give
(in some cases very) different results on different hardware and
different workloads.

If you have the time, motivation and a suitable testcase you can check
what works best for you. In the majority of cases this seems to be
HT disabled/SCHED_4BSD though.

	Regards, Joerg

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