second cpu not used on smp platform

LI Xin delphij at
Thu Jan 25 21:19:24 UTC 2007

Oles Hnatkevych wrote:
> Hello!
> Just cvsup-ed and upgraded to 6.2-STABLE.
> The box has hyperthreading processor:
> # more /var/run/dmesg.boot |grep -i cpu
> CPU: Intel(R) Pentium(R) 4 CPU 3.00GHz (3000.37-MHz 686-class CPU)
>   Logical CPUs per core: 2
> 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!
> What it can be????

This is done intentionally on all -STABLE branches, see for details.

Note that it is possible to re-enable htt if you know what you are
doing, by setting machdep.hyperthreading_allowed.  Please note that
enabling hyperthreading does hurt performance for many cases, so you
will want to evaluate if you really want it, or to disable it from BIOS.

Xin LI <delphij at>
FreeBSD - The Power to Serve!

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