An efficient uniform run-time scheme for mixed regular-irregular applications

Abstract

Almost all applications containing indirect array addressing (irregular accesses) have a substantial number of direct array accesses (regular accesses) too. A conspicuous percentage of these direct array accesses usually require interprocessor communication for the applications to run on a distributed memory multicomputer. This study highlights how lack of a uniform representation and lack of a uniform scheme to generate communication structures and parallel code for regular and irregular accesses in a mixed regularirregular application prevent sophisticated optimizations. Furthermore, we also show that code generated for regular accesses using compile-time schemes are not alzvays compatible to code generated for irregular accesses using run-time schemes. In our opinion, existing schemes handling mixed regular-irregular applications either incur unnecessary preprocessing costs or fail to perform the best communication optimization. This study presents a uniform scheme to handle both regular and irregular accesses in a mixed regularirregular application. While this allows for sophisticated communication optimizations such as message coalescing, message aggregation to be made across regular and irregular accesses, the preprocessing costs incurred are likely to be minimum. Experimental comparisons for various benchmarks on a 16-processor IBM SP-2 show that our scheme is feasible and better than existing schemes.