Access descriptor based locality analysis for Distributed-Shared Memory multiprocessors

Most of today's multiprocessors have a Distributed-Shared Memory (DSM) organization, which enables scalability while retaining the convenience of the shared-memory programming paradigm. Data locality is crucial for performance in DSM machines, due to the difference in access times between local and remote memories. In this paper, we present a compile-time representation that captures the memory locality exhibited by a program in the form of a graph known as Locality-Communication Graph (LCG). In the LCG, each node represents a DO loop nest which can have at most one level of parallelism. Not all loops need to be represented within a node and, therefore, the LCG may contain cycles. Our representation works whether the loops represented by the nodes are perfectly nested or not, and the subscript expressions and loop limits can be affine or non-affine expressions of the loop indices. The LCG provides essential information that a parallelizing compiler can use to automatically choose a good iteration/data distribution and to schedule the communication operations required during program execution.