How is hyperthreading handled on amd64?

[John Baldwin]

On Tuesday 14 March 2006 09:36, Bill Moran wrote:
> On Mon, 13 Mar 2006 15:32:51 -0500
> John Baldwin <jhb at freebsd.org> wrote:
> 
> > On Monday 13 March 2006 15:04, Bill Moran wrote:
> > > On Mon, 13 Mar 2006 14:06:34 -0500
> > > John Baldwin <jhb at freebsd.org> wrote:
> > > 
> > > [...]
> > > > > I can't argue that the boot messages don't seem to show anything to
> > > > > indicate that a second logical CPU was found.
> > > > 
> > > > Grab the dmesg from /var/run/dmesg.boot rather than /var/log/messages
> > > > please.
> > > 
> > > Copyright (c) 1992-2005 The FreeBSD Project.
> > > Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
> > > 	The Regents of the University of California. All rights reserved.
> > > FreeBSD 6.0-RELEASE-p5 #1: Fri Mar 10 16:57:56 EST 2006
> > >     root@:/usr/obj/usr/src/sys/DB64
> > > Timecounter "i8254" frequency 1193182 Hz quality 0
> > > CPU: Intel(R) Xeon(TM) CPU 3.00GHz (2992.71-MHz K8-class CPU)
> > >   Origin = "GenuineIntel"  Id = 0xf41  Stepping = 1
> > >   Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
> > >   Features2=0x641d<SSE3,RSVD2,MON,DS_CPL,CNTX-ID,CX16,<b14>>
> > >   AMD Features=0x20000800<SYSCALL,LM>
> > >   Hyperthreading: 2 logical CPUs
> > > real memory  = 2147221504 (2047 MB)
> > > avail memory = 2066378752 (1970 MB)
> > > ACPI APIC Table: <DELL   PE BKC  >
> > > FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
> > >  cpu0 (BSP): APIC ID:  0
> > >  cpu1 (AP): APIC ID:  1
> > 
> > This is a dmesg from an SMP kernel this time. :)
> > 
> > Can you provide the output from 'sysctl machdep'?
>
> machdep.hlt_cpus: 2
> machdep.hlt_logical_cpus: 0
> machdep.logical_cpus_mask: 2
> machdep.hyperthreading_allowed: 0

Ok, the mask is right (CPU 1 is marked as a hyperthread), and
it's marked as disabled in hlt_cpus.  I think I know what is
happening.  Can you update to the latest RELENG_6 and see if the
issue still occurs.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org