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3 – Using InfiniPath MPI
Getting Started with MPI
3-2 IB6054601-00 D
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These examples assume that:
■ Your cluster administrator has properly installed InfiniPath MPI and the
PathScale compilers.
■ Your cluster’s policy allows you to use the mpirun script directly, without having
to submit the job to a batch queuing system.
■ You or your administrator has properly set up your ssh keys and associated files
on your cluster. See section 3.5.1 and section 2.9 for details on
ssh
administration.
To begin, copy the examples to your working directory:
$ cp /usr/share/mpich/examples/basic/* .
Next, create an MPI hosts file in the same working directory. It contains the host
names of the nodes in your cluster on which you want to run the examples, with
one host name per line. Name this file
mpihosts. The contents can be in the
following format:
hostname1
hostname2
...
There is more information on the mpihosts file in section 3.5.6.
3.3.1
An Example C Program
InfiniPath MPI uses some shell scripts to find the appropriate include files and
libraries for each supported language. Use the script
mpicc to compile an MPI
program in C and the script
mpirun to execute it.
The supplied example program
cpi.c computes an approximation to pi. First,
compile it to an executable named
cpi.
$ mpicc -o cpi cpi.c
mpicc, by default, runs the PathScale pathcc or gcc compiler, and is used for
both compiling and linking, exactly as you'd use the
pathcc command.
NOTE: On ppc64 systems, gcc is the default compiler. For information on using
other compilers, see section 3.5.3.
Then, run it with several different specifications for the number of processes:
$ mpirun -np 2 -m mpihosts ./cpi
Process 0 on hostname1
Process 1 on hostname2
pi is approximately 3.1416009869231241,
Error is 0.0000083333333309
wall clock time = 0.000149