Re: How useful is Hyper-Threading for average user?

On Tue, 12 Aug 2003 16:54:50 -0400, John Brock wrote:

> I'm planning on buying a new PC this week (there's a sale!), and I have
> the option of buying a 2.8GHz P4 with a 533MHz FSB or a 2.8GHz P4 with
> Hyper-Threading and an 800MHz FSB for almost the same price. My first
> question is does this matter at all for the average user (word processing,
> web browsing, multi-media, etc.)?
>
> I also want to understand a little better what is going on. It sounds
> like HT is equivalent to a dual CPU on a single chip. Is that right? Is
> the 2.8GHz HT system effectively the equivalent of a hypothetical system
> with two physical non-HT 2.8 GHz CPUs? Does that mean that if I am
> running a compute intensive process in the background the HT system will
> assign it to one virtual CPU while the other is entirely free for whatever
> else I might want to do? That certainly sounds like it would occasionally
> be useful, and certainly worth the small extra price.
>
> But are there any drawbacks? Any at all? Is there *any* operating system
> or application which will choke or fail to run properly on an HT system?
> (I'm not talking about failing to fully take advantage of both virtual
> CPU's, I mean actually failing). If I want to run Linux (or BSD, or
> MS-DOS for that matter) will I *ever* run into problems?
>
> And what about heat. Is the HT system hotter, enough that it might
> matter? Speed is nice, but I value stability and compatibility more
> highly. So will HT ever hurt me in those areas?

Hyper-Threading increases throughput slightly at the expense of single
thread performance. I ran an experiment on my dual Xeon system where I did
makes of Wine with different -j switches, 1,2 and 4, and hyperthreading on
and off. With hyperthreading on the make -j 4 (four threads) ran about 10%
faster, but the makes with -j 1 and -j 2 (one and two threads) ran 25%
slower. Future Pentium implementations may fix this but for now you should
keep mutlithreading off. As for the faster front side bus, faster memory
should always be a good thing so I'd buy the processor with the faster FSB
assuming the price premium is small, but if the price premium is more than
$75 I'd go with the slower FSB processor.