detecting hyperthreading

[Rui Paulo]

On 10 Mar 2015, at 06:03, Pokala, Ravi <rpokala at panasas.com> wrote:
> 
> Hi folks,
> 
> There used to be a sysctl, "machdep.hyperthreading_allowed", which
> indicated whether or not the kernel was using hyperthreaded cores. It
> looks like it was removed sometime between 8 and 9, for perfectly good
> reasons (https://svnweb.freebsd.org/base?view=revision&revision=222853).
> 
> That said, is there currently a way to tell at runtime from userland if
> hyperthreading is enabled or not?

I think that sysctl didn't fully control hyperthreading: you can disable it on the BIOS and FreeBSD never exported that information.  If you used that tunable, it would simply disable the Pentium 4 Hyperthreading.

--
Rui Paulo