Visualising parallel numerical software performance on a shared memory multiprocessor

We consider here the use of a software package which can be used to monitor and visualise the behaviour, with respect to data accesses, of parallel software in a multiprocessor environment supporting shared memory. The purpose of such monitoring is two-fold: to aid in the understanding of the behaviour of a given algorithm, and to support the debugging of that software. To illustrate the use of this package we analyse its facilities in connection with a parallel implementation of block Gaussian elimination to solve a system of equations which arises when a certain spectral method is employed to solve an elliptic partial differential equation in two dimensions. We outline the method, indicate the synchronisation mechanisms which are necessary to ensure that the correct sequence of operations take place, and briefly describe the facilities provided by Encore Parallel Fortran which support these mechanisms. We then examine the facilities of the visualisation software and indicate how these were adapted to monitor accesses to a packed storage representation of a block sparse array. Finally we illustrate the use of the software in the context of the solution of a particular partial differential equation.