An application-driven study of multicast communication for write invalidation

In distributed shared-memory (DSM) multiprocessors, a write operation requires multiple messages to invalidate the nodes which share and cache the memory block to being written. The consequent write stall time impedes the performance of such systems. An effective means of achieving efficient invalidation is to employ multicast messages to reach the sharing nodes. This study evaluates two multicast-based invalidation schemes, dual-path and pruning, by performing application-driven simulation. The experimental settings used herein find that multicasts improve invalidation traffic for four of the six evaluated real applications. The remaining two applications are computationally intensive, and multicast-based invalidation is less effective. However, since multicasts encourage bursty communication, our results indicate that they help relieve network congestion during these periods. Dual-path performs slightly better than pruning, because it is less sensitive to routing delay in the routers. Our results further demonstrate that cache size is an important design parameter for multicast-based invalidation, and is highly effective for DSM multiprocessors with larger caches.