Re: How to enable/use Hyperthreading?

[Colin <cwvca_SPAMNOT@hotmail.com>]

Rogério Brito wrote:
> I bought recently a new computer with a Pentium D processor (which is
> supposed to have two cores, if I understand it) and one of the first
> things that I did with it was to enable SMP.
>

I don't think Pentium D processors are suppose to have two cores.  Some
of them have hyperthreading which can make then behave like they have
two cores.

> Seeing in /proc/cpuinfo that the CPU supports Hyperthreading (the ht
> flag is in the supported CPU features of this computer), 

Just because the ht flag is there doesn't mean that supports
hyperthreading (strange but true).

> I compiled a
> brand new kernel (2.6.19-rc4 at the time) and answered Yes to the option
> of using Symmetrict Multithreading (aka Hyperthreading in Intel-speak).
> 
> I posted things that I thought were relevant at
> http://www.ime.usp.br/~rbrito/pentium-d/ and it shows two processors,
> but I don't actually know if they are two "real" processors (cores) or
> two "virtual" processors (1 processor with hyperthreading).

Again, I think you have one core which looks like two processors.

> Also, the dmesg put there doesn't mention that the system has
> hyperthreading enabled after I booted it with the acpi=ht kernel
> option.

If you run "top" and see some process names with "/0" or "/1" at the
end, then you are running an "smp" kernel.