[Beowulf] Single Processor vs SMP

Jeffrey B. Layton laytonjb at comcast.net
Fri Feb 27 16:23:23 EST 2004


   I hoping someone will jump and say that the answer depends
upon the code(s) you're running. If possible test your codes on
a dual CPU box with one copy running and then two copies
running (make sure one copy is on one CPU). Test this on the
architectures you are interested in. If you can also test on
multiple nodes with some kind of interconnect to judge how
the code(s) scale with number of nodes and with interconnect.
   For example, at work I use a code that we tested on single
and dual CPU machines. It was an older PIII/500 box that used
the old Intel 440BX chipset (if I remember correctly). We
found that running two copies only resulted in a 30% penalty
for running duals.
   We also tested on a cluster with Myrinet and GigE. Myrinet
only gave this code about a 2% decrease in wall clock time
(we measure speed in wall clock time since that is what is
important to us).
   Then we got quotes for machines and did the price/performance
calculation and determined which cluster was the best.
    I highly recommend doing the same thing for your code(s).
Be sure to check out Opterons since they have an interesting
memory subsytem that should allow your codes to have little
penalty in running on dual machines ("should" is the operative
word. You should test your codes to determine if this is true).

Good Luck!


>I'm currently working in a physics department that is in the process of
>building a high performance Beowulf cluster and I have some doubts in
>terms of what type of hardware to acquire.
>The programming systems that will be used are MPI and HPF. Does anyone
>knows any study comparing the performance of single cpu machines vs smp
>machines or even between the several cpu's available (intel p4, amd athlon,
>powerpc g5, ...)?
>Thanks for any advice

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