Due 2024-10-01.

The goal of this homework is to get you up and running on Perlmutter.

Logging in

The NERSC documentation has information about how to connect to Perlmutter. The short version is “use ssh”, but I strongly recommend using ssh with the sshproxy setup to avoid typing your password (and one-time password) repeatedly. With the proxy set up, you should only need to enter your password (including one-time password) once every 24 hours.

Loading modules

When you log into Perlmutter, you start off with a fairly minimal set of tools available in the standard path. A variety of compilers and other tools are all available, but you will need to learn a little about environment modules to use them.

On Perlmutter there are standard compiler wrappers for building parallel codes. These compiler wrappers include all the requisite compiler and linker directives to make sure that things are set up. Make sure that you use the compiler wrappers (typically called cc, CC, and ftn for C, C++, and Fortran) when you compile in order to get this convenience. The compilers are also set up so that they target the appropriate behavior for the compute nodes.

Programming models

We will be learning to use MPI and OpenMP, which is the recommended programming model on Perlmutter. We will be starting with MPI. The default MPI on Perlmutter is the Cray MPI implementation.

Running jobs

NERSC uses a job queue system based on Slurm. Users submit jobs to a queue (using sbatch) with some set of parameters describing resources that will be used. The script that is submitted includes additional parameters, shell commands to set up the appropriate environment, and shell commands to run whatever is to be run. There is an example submission script in the class demos repository.

It sometimes takes a bit for things to run, and it is not so easy to tell whether a code is taking a while because it has not been scheduled or because something has gone wrong. You can use the sqs and squeue monitoring tools to check on the status of a running job.

It is considered bad form to run anything computationally intensive on the login nodes.

Your tasks

You have two tasks:

• Run the MPI ping-pong example from the demos subdirectory and submit your timings from on Perlmutter.
• Complete the telephone code.