The Impact of Link Arbitration on Switch Performance

Switch design for interconnection networks plays an important role in the overall performance of multiprocessors and computer networks. In this paper we study the impact of one parameter in the switch design space, link arbitration. We demonstrate that link arbitration can be a determining factor in the performance of current networks. Moreover, we expect increased research focus on arbitration techniques to become a trend in the future, as switch architectures evolve towards increasing the number of virtual channels and input ports. In the context of a state-of-the-art switch design we use both synthetic workload and execution driven simulations to compare several arbitration policies. Furthermore, we devise a new arbitration method, Look-Ahead arbitration. Under heavy traffic conditions the Look-Ahead policy provides significant improvements over traditional arbitration schemes without a significant increase in hardware complexity. Also, we propose a priority based policy that is capable of reducing the execution time of parallel applications. Lastly, we enhance the arbitration policies by a supplemental mechanism, virtual channel reservation, intended to alleviate the hot-spot problem.