What good are shared-memory models?

Abstract

Shared memory models have been criticized for years for failing to model essential realities of parallel machines. Given the current wave of popular message-passing and distributed memory models (e.g., BSP, LOGP), it is natural to ask whether shared memory models have outlived any usefulness they may have had. In this paper we discuss the continuing importance of shared memory models in the design and analysis of parallel algorithms. We describe a new model, the Queuing Shared Memory (QSM) model, that accounts for limited communication bandwidth while still providing a shared memory abstraction, and provide evidence of its practicality. Finally, we discuss important areas for future models research. We argue that the compelling need for parallel computing in large scale data analysis (e.g., decision support, data mining) implies that the most important modeling issue going forward concerns how best to model disk I/O.