Using problem topology in parallelization
Liebrock, Lorie M.
Doctor of Philosophy
Problem topology is the key to efficient parallelization support for partially regular applications. Specifically, problem topology provides the information necessary for automatic data distribution and regular application optimization of partially regular applications. Problem topology is the dimensionality, size, and connectivity of the problem. Problem topology has traditionally been used in explicit parallelization of regular problems such as physical simulation applications. In languages such as High Performance Fortran, problems that are regular allow many optimizations not applicable to irregular application codes. Unfortunately, many applications must sacrifice regularity to some extent for computational efficiency. This research focuses on partially regular problems and strives to take advantage of partial regularity in the parallelization and compilation process. This dissertation uses topology for automatic, natural-topology, data distribution in linearized and composite grid (or multiblock) applications. For linearized applications, Fortran D is extended with logical topology and index array specifications. With the information provided in these specifications, it is shown how regular, linearized applications can be parallelized automatically in Fortran D as regular computations using their natural topology. In composite grid problems, meshes are coupled to form larger, more complex topology structures. Composite grid problems arise in important application areas such as fluid flow simulation, aerodynamic simulation, electric circuit simulation, and nuclear reactor simulation. Such physical phenomenon are inherently parallel and their simulations are computationally intensive. This dissertation presents a programming style and template for writing High Performance Fortran programs for these applications, algorithms for automatic distribution of composite grid applications with mesh configurations included in the input, and a discussion of compiler issues for composite grid problems. The automatically generated distributions for composite grid applications guarantee that all communication associated with the distribution of any given mesh will remain regular and nearest-neighbor in the mapping to processors. This research allows High Performance Fortran compilers to perform regular application optimizations on the codes for this class of partially regular applications. Finally, the research is supported by experimental results, which indicate that substantial performance improvements are possible when topology is used in the parallelization of partially regular applications.