Can't see second CPU in FreeBSD 5.4-p6

[Nigel Wohlers]

joseph kacmarcik wrote:
> hello's!
> 
> i've recently installed freebsd 5.4 and patched up to p6. since the
> install and up to this patch level, i'm not certain the second cpu
> (hyperthreading, not physical cpu) is being used. i guess it could just be
> top not showing it, cuz it's in my kernel and in dmesg.
> 
> relevant kernel lines are:
> options         SCHED_4BSD
> options         SMP
> device          apic
> 
> and relevant dmesg output is:
> CPU: Intel(R) Pentium(R) 4 CPU 2.80GHz (2795.24-MHz 686-class CPU)
>   Hyperthreading: 2 logical CPUs
> FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
>  cpu0 (BSP): APIC ID:  0
>  cpu1 (AP): APIC ID:  1
> cpu0: <ACPI CPU> on acpi0
> cpu1: <ACPI CPU> on acpi0
> SMP: AP CPU #1 Launched!
> 
> 
> when using top, i always see CPU0, and the column under 'C' is always 0.
> 
> is there another tool i can use to see cpu scheduling or am i missing
> something obvious (or obscure)?
> 
> for the record, i've tried more than one cpu, and freebsd 5.2.1 was able
> to see and use two cpu's with the same hardware.
> 
> insight appreciated!
> joe


Hyperbollocks is disabled by default.

See /usr/src/UPDATING entry for 20050513:

         Intel Hyper-Threading is now disabled by default due to a
         security issue, but can be re-enabled by setting the
         machdep.hyperthreading_allowed tunable in /boot/loader.conf.