On Mon, 7 Mar 2005 22:21:05 +0100, Christian Gütter <news@...> wrote:

>
> > Those Xeon thingies have multiple-core CPUs.
>
> AFAIK a Xeon processor is a single-core CPU.
> HT processors have an additional set of registers, an additional APIC,
> and some other small modifications, but they do not have a second
> core.

Yeah, I noticed later that the term "multi-core" isn't quite appropriate.

> > They call it ``HyperThreading''
> > or ``HT'', for short. Hyperthreading is very similar to real SMP,
>
> HT, also called SMT (Simultaneous Multithreading), is quite different
> from SMP. With HT enabled, the OS sees two processors, but there is
> only one processor/core. To make use of HT (i.e. to gain a performance
> benefit from it), the OS scheduler must be aware of HT.
> The scheduler of Windows 2000, for example, is not aware of HT. It
> detects two CPUs and thinks it works on a SMP system. Many people have
> even reported a little performance drain with HT and Win2000, so it is
> better to turn of HT on a Win2000 system.

I really don't know about Windows... and I assumed he's using Linux anyways.
Linux has a HT-aware scheduler since 2.6 (well, actually since the 2.5
development tree). And well, with an HT-aware scheduler the benefits are
similar to SMP, but I guess less expensive in the synchronisation.

I forgot that some/most distro still use 2.4...
I'd always try to use the latest stable kernel anyways.
So, if you're using Linux, Dirk, make sure that you use a 2.6 line kernel.

> However, I am currently working with a dual Xeon system with HT enabled and Firebird
> runs fine on it. Maybe this is just luck.

Now that you mention it, I think we have a dual-Xeon server at work, too.
I'll check this when I'm back at my workplace.
I just know that FB is running fine. :)

cu,
Daniel

--
eat(this); // delicious suicide