Architectural Adaptability in Parallel Programming via Control Abstraction

Parallel programming involves finding the potential parallelism in an application, choosing an algorithm, and mapping it to the architecture at hand. Since a typical algorithm has much more potential parallelism than any single architecture can effectively exploit, we usually program the parallelism that the available control constructs easily express and that the given architecture efficiently exploits. This approach produces programs that exhibit much less parallelism than the original algorithm and whose performance depends entirely on the underlying architecture. To port such a program to a new architecture, we must rewrite the program to remove any ineffective parallelism and to recover any lost parallelism appropriate for the new machine. In this paper we show how to adapt a parallel program to different architectures using control abstraction. With control abstraction we can define and use a rich variety of control constructs to represent an algorithm's potential parallelism. Since control abstraction separates the definition of a construct from its implementation, a construct may have several different implementations, each exploiting a different subset of the parallelism admitted by the construct. By selecting an implementation for each control construct using annotations, we can vary the parallelism we choose to exploit without otherwise changing the source code. This approach produces programs that exhibit most of, if not all, the potential parallelism in an algorithm, and whose performance can be tuned for a specific architecture simply by choosing among the various implementations for the control constructs in use