Hyperthreading question

[Dwayne MacKinnon]

Hello,

	I'm in charge of upgrading a number of boxes from 4.8-RELEASE from 
4.10-RELEASE. My problem is this section of notes from the 4.9-RELEASE 
errata:

(28 Oct 2003) Very late in the release cycle, a change was made to the 
HyperThreading (HTT) support on Intel® processors. HTT support is now 
enabled by default on SMP-capable kernels; as a result, the HTT kernel 
option is unnecessary and has been removed. The extra logical CPUs are 
always started so that they can handle interrupts, but are prevented 
from executing user processes by default. To enable the logical CPUs, 
change the value of the machdep.hlt_logical_cpus sysctl(8) variable from 
1 to 0. This value can also be set from the loader as a tunable of the 
same name. This behavior is now identical to FreeBSD 5.X.

	My boss is pretty adamant about not wanting the logical CPUs started at 
all, let alone having them available for user processes. So, I'm 
wondering if there's any straightforward way to disable them. Kernel 
hacking is not a problem... we use custom kernels in our work anyway. 
But I'd really appreciate a pointer in the right direction, as well as a 
general idea of how difficult my life will get if I attempt this.

	(Note that I attempted to disable HT support in the BIOS. It didn't 
have any effect. The logical CPUs still launched.)

Thanks,
DMK