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Vendor: “There are currently two systems available, each with two 8-core Xeon E5-2670 processors, 32GB memory, 120GB SSD and two Tesla K20 GPUs. The hostnames are master and node2. You will see that a GPU-accelerated version of LAMMPS with MPI support is installed in /usr/local/LAMMPS.”

Actually, turns out there are 32 cores on node so I suspect four CPUs.

First, we expose the GPUs to Lammps (so running with a value of -1 ignores the GPUs) in our input file.

# Enable GPU's if variable is set.
if "(${GPUIDX} >= 0)" then &
        "suffix gpu" &
        "newton off" &
        "package gpu force 0 ${GPUIDX} 1.0"

Then we invoke the Lammps executable with MPI.

NODES=1      # number of nodes [=>1]
GPUIDX=0     # GPU indices range from [0,1], this is the upper bound.
             # set GPUIDX=0 for 1 GPU/node or GPUIDX=1 for 2 GPU/node
CORES=12     # Cores per node. (i.e. 2 CPUs with 6 cores ea =12 cores per node)

which mpirun

echo "*** GPU run with one MPI process per core ***"
date
mpirun -np $((NODES*CORES)) -bycore ./lmp_ex1 -c off -var GPUIDX $GPUIDX \
       -in film.inp -l film_1_gpu_1_node.log
date

Some tests using lj/cut, eam, lj/expand, and morse:

• CPU only 4 mins 30 secs
• 1 GPU 0 mins 47 secs (a 5-6 times speed up)
• 2 GPUs 0 mins 46 secs (never saw 2nd GPU used, problem set too small?)

Some tests using a restart file and using gayberne,

• CPU only 1 hour 5 mins
• 1 GPU 3 mins and 33 secs (a 18-19 times peed up)
• 2 GPUs …

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