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SubjectRe: SMP question

On 06.12, Scott Robert Ladd wrote:
> J.A. Magallon wrote:
> > In short, for FP intensive tasks, hyperthreading is a big lie...
> > You can't run 2 computations in parallel.
>
> Yes and no; the benefit of HT depends on the application in question.
> I've seen everything from a 5% LOSS in performance to a 30% INCREASE in
> performance, for intensive floating-point code. This is with programs
> parallelized with OpenMP and Intel's C and Fortran compilers. I'm still
> analyzing the exact nature of the benefits, but they *do* exist.
>
> While I much prefer multiple physical CPUs to "virtual" CPUs, HT *does*
> provide performance improvements for certain applications. To call HT a
> "big lie" is both provacative and inaccurate.
>

I told that because non-techical people just think they are buying _two_
processors, but they really pay too much for 1.25 processors, and that
if you fine-tune your code...

--
J.A. Magallon <jamagallon@able.es> \ Software is like sex:
werewolf.able.es \ It's better when it's free
Mandrake Linux release 9.2 (Cooker) for i586
Linux 2.4.21-rc8-jam1 (gcc 3.3 (Mandrake Linux 9.2 3.3-1mdk))
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