[TriLUG] Hyperthreading and Xeons

[William Sutton]

Would this be the reason that under Gentoo my dual Xeon 2GHz has a 
tendency to lock up?  I was using 2.4 stock kernels with HT enabled in the 
bios.

William

On Wed, 13 Oct 2004, John Franklin wrote:

> 
> On Oct 13, 2004, at 1:06 PM, Jeremy Portzer wrote:
> 
> > So, I got my first Xeon server recently, and although it's really dual
> > 2.6 GHz, it shows as four processors to Linux.
> >
> > Does this mean that I should treat it as a four-processor computer for
> > the purposes of starting processes?  For example, I have a program that
> > runs as many copies of itself as there are processors (but you have to
> > tell it how many processors there are).  Should I let it run four 
> > copies
> > or stick with two?
> >
> > Any other consequences to hyperthreading I should know about?
> 
> One of the big issues with HT is that it looks like SMP to HT-unaware 
> kernels.  The difference between SMP and HT is the shared resources on 
> the chip.  When moving a process to a second CPU (core), an HT-unaware 
> kernel may blow the CPU cache, move the process to the second core 
> thinking it's a physically separate CPU, and refill the CPU cache.  An 
> HT-aware kernel will move the process w/o blowing the cache.
> 
> I don't know which Linux kernels (if any) are fully HT aware.
> 
> jf
>