Re: detecting hyperthreading in linux 2.4.19

[John Bradford]

> > Is there a way for a userspace program running on linux 2.4.19 to tell
> > the difference between a single hyperthreaded xeon P4 with HT enabled
> > and a dual hyperthreaded xeon P4 with HT disabled? The /proc/cpuinfos
> > for the two cases are indistinguishable.
> 
> I don't know of any way to do this in userland.  The whole point is that the 
> sibling processors are supposed to look like real ones.
> 
> You _could_ try running two processes simultaneously in tight spin loops for 
> 100 million cycles and comparing the amount of real time consumed.  That 
> would be rather unreliable and kludgey though.

If /proc/interrupts shows a processor is handling interrupts then it
is definitely a 'real' one.  If it isn't handling interrupts, it may
or may not be a 'real' one.  That's another unreliable and kludgey way
to tell the difference :-).

John.