[gmx-users] Haphazard Results with LAM-MPI

[David]

On Wed, 2003-04-09 at 06:13, Venkat Ramanan K wrote:
> Hi,
> 
> We are a bunch of undergraduate students and have put up a cluster 
> of 16 IBM's using LAM for the purpose of running GROMACS. During 
> our simulation test runs we noticed that the running time 
> increases as the number of nodes in the LAM topology increases. We 
> couldn't diagonise the problem...plz help.
> 
> We used the folowing commands:
> 
> grompp -v -f full -o full -c after_pr -p speptide -np 16 -shuffle 
> -sort
> 
> mpirun N -lamd -nger -nsigs mdrun -v -s full -o full -c after_full 
> -g flog

Apart from the number of atoms, using the options nger and lamd will
make communicationparticularly slow. These option are meant for
debugging LAM application.

You want to run 
mpirun -O -c2c -c N mdrun  etc.
where N is the number of nodes.

Furthermore the network that you are using can have an influence. Is it
100 Mbit/s, is it switched?

Check the results on the benchmark web page. We have results for a
switched network and as long as you have a reasonably large system (and
no PME) it scales half decent at least.


> 
> We got the following running times with GROMACS 3.1.4...
> 
> 1 node - 13hrs 5:27
> 2 nodes - 16hrs 12:59
> 4 nodes - 17hrs 32:14
> 8 nodes - 45hrs 00:36
> 16 nodes - 45hrs 46:55
> 
> Thanks in advance
> 
> Venkat
> 
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-- 
Groeten, David.
________________________________________________________________________
Dr. David van der Spoel, 	Dept. of Cell and Molecular Biology
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://xray.bmc.uu.se/~spoel
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