[gmx-developers] MPI slower than Non-MPI gromacs

Erik Lindahl lindahl at csb.stanford.edu
Wed Feb 18 09:47:25 CET 2004

Hi William,

The Gromacs demo is an extremely small system. Since the innerloops are 
coded in assembly it probably needs in the order of a millisecond to do 
a step, and your MPI latencies are likely higher than this (or at least 
in the same ballpark) if you are using the TCP/IP stack in windows and 

Test it with the DPPC membrane system from the benchmark pages at 



On Feb 18, 2004, at 3:26 AM, William Bagdan wrote:

> Hi
> For win32 I have compiled MPICH, FFTW 2.1.5 with MPICH and then 
> Gromacs 3.1.4 with MPI and the FFTW with MPI.  After Testing the MPICH 
> and FFTW with MPI, I then began testing the GMXDemo using MPI.  The 
> results are not reassuring.  With MPI the time is longer than just 
> running straight Gromacs without the MPI.  Anybody have any ideas?  I 
> defined USE_MPI, but am not sure if I need to set some other defines 
> to get the FFTW.
> If anybody is interested I would be willing to give you the setup for 
> compiling everything and the instructions.
> William
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