Evaluation of alternative arbitration policies for Myrinet switches

Interconnection networks consist of a set of switches in-terconnected by point-to-point links, and hosts linked to those switches through a network interface card. These net-works are becoming increasingly popular as a cost-effective alternative to parallel computers. One of the most well-known example is the Myrinet network. These networks use techniques and incorporate components that have been suc-cessfully applied to interconnection networks for parallel computers. One of these techniques is the use of cross-bar chips as the main component of switches, allowing to connect the input channel of any of their ports to the out-put channel of any of their ports for forwarding incoming packets. Of course, when several packets request the same output channel, certain criterion must be used for select-ing one of them. This criterion may affect performance in terms of latency and throughput, specially in wormhole net-works (Myrinet) where a packet occupies several resources while it is waiting for the output channel. In Myrinet, an arbitration policy based on round-robin criterion is used. However, there exist other arbitration policies that, when applied to Myrinet networks, could increase their perfor-mance. In this paper, several arbitration policies for select-ing the packet for a free output channel have been consid-ered and evaluated. We have found that strategies based on injection time and remaining distance to travel reduce the average and maximum packet latency of the current policy used in Myrinet