kern/94410: Cannot disable hyperthreading if more than one phsyical processor exists

[petefrench at ticketswitch.com]

>Number:         94410
>Category:       kern
>Synopsis:       Cannot disable hyperthreading if more than one phsyical processor exists
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Mar 13 15:30:16 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     Web Administrator
>Release:        FreeBSD 6.0-RELEASE i386
>Organization:
Ticket Switch Ltd
>Environment:
System: FreeBSD websvr01.rattatosk 6.0-RELEASE FreeBSD 6.0-RELEASE #0: Wed Dec 28 21:55:17 GMT 2005 webadmin at turpentine.rattatosk:/usr/obj/usr/src/sys/RATTATOSK-SMP i386

	HP blade running 6.0-RELEASE

>Description:

	If an SMP kernel is run on a machine with more than one physical
	processor there seems to be no way to disable hyperthreading.
	The usual flags appear to set the masks correctly, but I am still
	seeing processes scheduled on 4 CPUs in 'top'. This machine
	only has two physical CPUs. In a machine with only one physical
	CPU then the behaviour works as expected.

>How-To-Repeat:

	Boot up 6.0 on a machine with more than one hyperthreading capabale
	processors installed, but with the flags turned off and observer
	that processes are still scheduled on all the hyperthreading processors.
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted: