[Beowulf] Picking a processor

Florent Calvayrac Florent.Calvayrac at univ-lemans.fr
Mon Dec 13 02:14:34 PST 2004

SF Husain wrote:
> Hi
> I'm currently designing a beowulf style parallel processor and am trying to
> decide which processor to use for the nodes. My project requires my final
> design for the parallel processor to be able to provide a sustained throuput
> of 0.25 TFlops.
> My research tells me that in general that the flop rate scales up linearly.
> My trouble is that I'm having trouble finding estimates for the flop rates
> of the processors I'm looking at.
> I've looked at the specfp2000 results but as far as I can tell their numbers
> do not easily convert to a flop rate. Could anyone tell me how I can find
> estimates for the flop rates of processors or if there is any rough sort of
> conversion that I can do on these spec (or any other) benchmark results.
> I'm aware that the actual rate is dependent on type of work given  to the
> processors. However my project is only a design exercise aimed at developing
> research skills so even a very rough conversion or sourse of sample results
> would be suitable for my purposes.

you should either focus on codes whose cost is well
known (system resolution in Scalapack), hence
speed easy to compute, or if you are using
a custom program run it with either hard or soft
performance counters (code instrumenting), which can be quite reliable
within a 50% margin of error.

 From my experience you get say 100 MFlops per Ghz
on a normal Pentium and a reasonably well written
typical computational code (not too optimized).

If you use linear algebra and large matrixes (more than 10000 squared)
  only with, say, ATLAS, you can
get theoretical performance (ie 1GFlops / GHz on
a Pentium). If you look at specialized hardware
(workstations, vector computers) you can get much more
  than that, and if you run physicist grade Fortran with
complicated formulas  or self-proclaimed IT expert C++ with heavy 
objects  and indirections, and not too much effort in cache locality in 
either case  you get only  20 MFlops/Ghz.


Florent Calvayrac  | Tel : 02 43 83 26 26  | Fax : 02 43 83 35 18
Laboratoire de Physique de l'Etat Condense | UMR-CNRS 6087
Inst. de Recherche en Ingenierie Moleculaire et Matx Fonctionnels
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