HTT on single CPU?

John Baldwin jhb at
Tue Jul 8 12:04:45 PDT 2003

On 08-Jul-2003 Tom Samplonius wrote:
> On Tue, 8 Jul 2003, John Baldwin wrote:
> ...
>> > I would need to look a second time, but there is no such BIOS option, and
>> > "options HTT" was nuked in 5.1, replaced by machdep.hlt_logical_cpus,
>> > which I don't have on my system.
>> You need to enable SMP and APIC_IO in your kernel to use HTT.  Also,
>> the BIOS setting probably won't make a difference.
>   Well, not all P4 CPUs are capable of HyperThreading.  It has to be
> fairly new.  Plus, only certain motherboard chipsets seem capable of
> supporting HyperThreading.  I would suspect that the BIOS has no
> HyperThreading options, it probably doesn't even support it.

If he gets the printf in his dmesg, his CPU supports it.  It is true
that his BIOS may not support it.  Currently, we require that the BIOS
provide an MP Table so that we can route interrupts via the APICs.
If an MP Table is not present but an acpidump does contain an APIC (MADT)
table that lists two CPU's, then it will eventually work, just not right


John Baldwin <jhb at>  <><
"Power Users Use the Power to Serve!"  -

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