7.3 Using MPICH with Rocks

Before we leave Rocks, let's look at a programming example you can use to convince yourself that everything is really working.

While Rocks doesn't include MPI/LAM, it gives you your choice of several MPICH distributions. The /opt directory contains subdirectories for MPICH, MPICH-MPD, and MPICH2-MPD. Under MPICH, there is also a version of MPICH for Myrnet users. The distinctions are described briefly in Chapter 9. We'll stick to MPICH for now.

You can begin by copying one of the examples to your home directory.

[sloanjd@frontend sloanjd]$ cd /opt/mpich/gnu/examples

[sloanjd@frontend examples]$ cp cpi.c ~

[sloanjd@frontend examples]$ cd

Next, compile the program.

[sloanjd@frontend sloanjd]$ /opt/mpich/gnu/bin/mpicc cpi.c -o cpi

(Clearly, you'll want to add this directory to your path once you decide which version of MPICH to use.)

Before you can run the program, you'll want to make sure SSH is running and that no error or warning messages are generated when you log onto the remote machines. (SSH is discussed in Chapter 4.)

Now you can run the program. (Rocks automatically creates the machines file used by the system, so that's one less thing to worry about. But you can use the -machinefile filename option if you wish.)

[sloanjd@frontend sloanjd]$ /opt/mpich/gnu/bin/mpirun -np 4 cpi

Process 0 on frontend.public

Process 2 on compute-0-1.local

Process 1 on compute-0-0.local

Process 3 on compute-0-0.local

pi is approximately 3.1416009869231245, Error is 0.0000083333333314

wall clock time = 0.010533

That's all there is to it.

Since Rocks also includes the High-Performance Linpack (HPL) benchmark, so you might want to run it. You'll need the HPL.dat file. With Rocks 3.2.0, you can copy it to your directory from /var/www/html/rocks-documentation/3.2.0/. To run the benchmark, use the command

[sloanjd@frontend sloanjd]$ /opt/mpich/gnu/bin/mpirun -nolocal \

> -np 2 /opt/hpl/gnu/bin/xhpl

...

(Add a machine file if you like.) You can find more details in the Rocks user manual.