Application of an object-oriented parallel run-time system to a Grand Challenge 3D multi-grid code

We have taken a Grand Challenge 3D multi-grid code, QGMG, initially developed on the Cray C-90 and subsequently parallelized for MPPs, and implemented it using the DUDE object-oriented, runtime system which combines both task and data parallelism. The QGMG code is a challenging application for two reasons. Firstly, as in all multigrid solvers, the most straightforward implementation requires that most of the processors idle at barrier synchronisations. Secondly, the QGMG code is an example of an application that requires both task and data parallelism: two multigrids (task parallelism) must be solved and each multigrid solver contains data parallelism. To address these challenges, DUDE loosens the requirement that all processes must wait at barriers, and provides integrated task parallelism and data parallelism. We describe the QGMG code and the DUDE object-oriented, runtime system in detail, explaining how we parallelized this Grand Challenge application.