Table-lookup based Crossbar Arbitration for Minimal-Routed, 2D Mesh and Torus Networks

Crossbar arbitration - which determines the allocation of output ports to packets in the input queues - is a performance-critical stage in the overall performance of routers for input-queued networks. The overall performance of crossbar arbitration depends on two metrics: (a) matching power - the ability of the arbiter to maximize the number of matches between requesting inputs and free outputs and (b) arbitration throughput - the number of such matches per unit time. Ideally, crossbar arbitration should maximize both metrics. Unfortunately, implementing high performance matching schemes compromises arbitration throughput. Similarly, simpler arbitration mechanisms that deliver high arbitration throughput offer lower matching power. The major contribution of this paper is the design of a table-lookup based crossbar arbitration mechanism - TabArb - that delivers superior matching and high arbitration throughput for minimal-routed, two dimensional mesh and torus networks. The two key innovations of TabArb are: (a) it forwards multiple requests from each input port to multiple output ports to expose adequate matching potential and (b) it employs precomputed tables that store maximum cardinality matches for all possible request combinations. Our technique improves the saturation throughput of adaptive routed mesh network by 14.8%. It offers little improvement for the DOR router due to limited opportunity.