Performance on a bandwidth constrained network: How much bandwidth do we need?

The authors approach network design from the perspective of the applications and ask how much network is needed. They answer this question, in the context of shared memory multiprocessors, for four scientific applications. They simulate their executions under infinite bandwidth assumptions and collect profiles of their varying bandwidth needs. These profiles are then fed into a performance model of how bursty traffic squeezes through a bandwidth constrained network. The results suggest that networks should provide a remote memory bandwidth of 2-4 bits/operation and memory module bandwidths of 8-16 bits/op. The higher memory module bandwidth is needed because of hot spots in the traffic patterns. Further simulations show that these hot spots arise primarily because or randomness and not because of multiple accesses to a single location. Thus, combining techniques will not eliminate hot spots from these applications.