enable smp / hyperthreading

[Robert Marella]

On Mon, 7 Nov 2005 20:05:24 +0100
Roland Smith <rsmith at xs4all.nl> wrote:

> On Mon, Nov 07, 2005 at 07:53:20PM +0100, jwl at io.dk wrote:
> > Hi
> > 
> > I've just installed 6.0-RELASE and am trying to get SMP to work (I
> > have af Pentium 4 with HT). So I've compiled the kernel with
> > 'options SMP' and according to dmesg the two CPUs are found:
> > 
> > FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
> >  cpu0 (BSP): APIC ID:  0
> >  cpu1 (AP): APIC ID:  1
> > 
> > But I'm not sure that both are enabled, because at this is at the
> > end of dmesg and I dont see the other CPU being enabled somewhere:
> > 
> > SMP: AP CPU #1 Launched!
> 
> I think it is referring to the Auxiliary Processor (AP), because the
> BSP (don't know what that stands for, though) is obviously already
> active. 
> > According to 'sysctl -a' there are 2 CPUs, but only 1 active and SMP
> > doesnt seem to be disabled:
> > 
> > kern.smp.cpus: 2
> > kern.smp.disabled: 0
> > kern.smp.active: 1
> 
>   sysctl -d kern.smp.active
>   kern.smp.active: Number of Auxillary Processors (APs) that were
>   successfully started
> 
> This is the number of _extra_ CPUs, which chould be 1.
>  
> Roland

If hyperthreading is working the ouput of 'top' should have a C column
and will show either a 0 or a 1.

AFAIK HTT is still disabled because of a security risk. See:

ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:09.htt.asc

If you do not believe you are at risk, there is a work around included
in the above site.

YMMV. I have been known to be wrong before. :-)

Robert