Re: NEED HELP: beowulf slower that single processor
Greetings! This sounds like the problem size you're running is too
small -- you need to make sure your code is parallelized at a "coarse
enough" grain to show the benefits of the cluster. Try a bigger
problem size, and see if the scaling is the same. Specifically, check
that you are running the same problem size as those who report success
with VASP on clusters.
Take care,
Stefano Curtarolo <auro@nietzsche.mit.edu> writes:
>
> Hi BeoGuys,
>
> I am actually using Linux Debian distribution 2.1 and I have setup a 8
> processors beowulf cluster. I am actually using portland compilers.
> I compiled mpich-1.2.0 and my application VASP (a density funcional
> software). I know that VASP is working well under other Beo-clusters, but
> not on mine :-(((((
> Adding more processors to mpirun -np MORE, I get a BIGGER total elaped
> time. For istance, with 2 processor, the USER time decreases of 70%
> (right, as it should do) but the system time explodes of 1 order or
> magnitude. speed(2 nodes, 2 processor) is almost same of speed(1 node, 1
> processor), but with 4 processors, the total speed is 1/3 of the original
> one. The system time is huge and the cluster is useless.
>
> So I supposed to have a problem in my network, since MPI is able to rsh
> everywhere, lauch jobs, and the mpi-benchmark says 6MBytes/seconds (which
> size ?). I have read the Linux TCP poor Performance:
> http://www.icase.edu/coral/LinuxTCP.html
> I have done this patch. No improvement.
> I have, 3com 905 10/100 (driver 0.99L) cards with a cabletron 100 switch,
> debian 2.1, PGI compiler suite, MPICH and LAM compiled with PGI
> compilers, vasp source (it has been reported going fast in a beo-cluster).
> Netpipe gives me some reasonable numbers for the bandwitdh.
>
> Thanks
>
> Stefano Curtarolo
>
>
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--
Camm Maguire camm@enhanced.com
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