Communication Optimizations Used in the Paradigm Compiler for Distributed-Memory Multicomputers

The PARADIGM (PARAllelizing compiler for DIstributed-memory General-purpose Multicomputers) project at the University of Illinois provides a fully automated means to parallelize programs, written in a serial programming model, for execution on distributed-memory multicomputers. To provide efficient execution, PARADIGM automatically performs various optimizations to reduce the overhead and idle time caused by interprocessor communication. Optimizations studied in this paper include message coalescing, message vectorization, message aggregation, and coarse gram pipelining. To separate the optimization algorithms from machine-specific details, parameterized models are used to estimate communication and computation costs for a given machine. The models are also used in coarse gram pipelining to automatically select a task granularity that balances the available parallelism with the costs of communication. To determine the applicability of the optimizations on different machines, we analyzed their performance on an Intel iPSC/860, an Intel iPSC/2, and a Thinking Machines CM-5.