Does multicast communication make sense in write invalidation traffic?

In distributed shared memory (DSM) multiprocessors, a write operation requires multiple messages to invalidate the nodes which share and cache the memory block to be written. The resulting write stall time is a performance hurdle to such systems. One approach to efficient invalidation is to use multicast messages to reach the sharing nodes. We use application driven simulation to evaluate two multicast based invalidation schemes: dual path (X. Lin and L.M. Ni, 1993) and pruning (M.P. Malumbres et al., 1996). Based on our experimental settings, we found that multicast improves invalidation traffic for four of the six evaluated real applications. The remaining two programs are computation intensive, and multicast based validation is less effective. But since they induce bursty communication, we found that multicasts help to relieve the network congestion during those periods of time. Dual path performs a little better than pruning, because it is less sensitive to routing delay in the routers. We also found that cache size is an important design parameter for multicast based invalidation. It is more effective for DSM multiprocessors with large caches.