Lazy release consistency for distributed shared memory
Keleher, Peter John
Doctor of Philosophy
A software distributed shared memory (DSM) system allows shared memory parallel programs to execute on networks of workstations. This thesis presents a new class of protocols that has lower communication requirements than previous DSM protocols, and can consequently achieve higher performance. The lazy release consistent protocols achieve this reduction in communication by piggybacking consistency information on top of existing synchronization transfers. Some of the protocols also improve performance by speculatively moving data. We evaluate the impact of these features by comparing the performance of a software DSM using lazy protocols with that of a DSM using previous eager protocols. We found that seven of our eight applications performed better on the lazy system, and four of the applications showed performance speedups of at least 18%. As part of this comparison, we show that the cost of executing the slightly more complex code of the lazy protocols is far less important than the reduction in communication requirements. We also compare the lazy performance with that of a hardware supported shared memory system that uses processors and caches similar to those of the workstations running our DSM. Our DSM system was able to approach, and in one case even surpass, the performance of the hardware system for applications with coarse-grained parallelism, but the hardware system performed significantly better for programs with fine-grained parallelism. Overall, the results indicate that DSMs using lazy protocols have become a viable alternative for high-performance parallel processing.