If your problem size is not large enough than any MPI program will
perform worse on a "large number" of nodes because of the overhead
involved in setting up the problem and network latency. Sometimes
that "large number" is as small as two :)
I am not at all familiar with DL POLY, but if you make the size of the
problem larger you should see more performance benefit because the
overhead will be small compared to the execution time.
Just in general I would say to start with a problem that takes at
least a minute on one node, run it a few times to see how much the run
time varies and then try it on two nodes. Especially if you are going
to try and scale it much past that initial two node version...
On 6/7/07, Aaron Thompson <aaron.p.thompson_at_[hidden]> wrote:
> Does anyone have experience using DL POLY with OpenMPI? I've gotten
> it to compile, but when I run a simulation using mpirun with two dual-
> processor machines, it runs a little *slower* than on one CPU on one
> machine! Yet the program is running two instances on each node. Any
> ideas? The test programs included with OpenMPI show that it is
> running correctly across multiple nodes.
> Sorry if this is a little off-topic, I wasn't able to find help on
> the official DL POLY mailing list.
> Thank you!
> Aaron Thompson
> Vanderbilt University
> users mailing list