Debugging GEOSgcm.x with Arm Forge at NCCS

Overview

This describes how to debug GEOS5 on NCCS systems (Discover) using the Arm Forge debugger (formerly Allinia DDT) and the remote client.

Prerequisites

This requires a build of GEOS built with the debug cmake options. See the GEOS5 build instructions for this.

Next you will need the Arm Forge remote client. This run on your local machine and basically provides a tunnel into the machine where your code actually runs. This is really the only practical way to debug as if you run Arm Forge on Discover it will be unusably slow due to needing to forward X. The remote client can be found here https://developer.arm.com/tools-and-software/server-and-hpc/downloads/arm-forge and installed in user space.

Running GEOSgcm.x in the Debugger

First a caveat. NCCS has a certain of Arm Forge licenses on the order of 100 to 200. What the user needs to know is that each license allows one MPI task to run so the practical result is that you can only run MPI with about 100 to 200 tasks. Therefore the user needs to have an experiment that can be run on that number of MPI tasks for this to be of use.