Portable programming within a message-passing model: the FFT as an example

This paper describes a portable programming environment for MIMD concurrent processors based on an object-oriented, message-passing paradigm. The basis of this environment is the Virtual Machine Loosely Synchronous Communication System (VMLSCS) which is designed to be used for loosely synchronous problems. VMLSCS is structured to make efficient use of hierarchical memory, and permits communication and calculation to be overlapped on certain concurrent processors. As an example, the use of VMLSCS in performing both one-dimensional and multi-dimensional fast Fourier transforms (FFTs) on concurrent multiprocessors is described. It is shown that all necessary interprocessor communication can be performed by a single routine, vm_index. Thus the construction of a portable concurrent FFT rests on the implementation of vm_index on the target machines. In the multi-dimensional algorithm a strip decomposition is applied to each of the directions in turn so that each of the FFTs performed in a particular direction are done in one processor. This allows fast sequential one-dimensional FFTs to be exploited. The implementation of vm_index on both homogeneous and inhomogeneous hypercubes, and shared memory multiprocessors is discussed.