Low-cost router microarchitecture for on-chip networks

Abstract

On-chip networks are critical to the scaling of future multi-core processors. The challenge for on-chip network is to reduce the cost including power consumption and area while providing high performance such as low latency and high bandwidth. Although much research in on-chip network have focused on improving the performance of on-chip networks, they have often relied on a router microarchitecture adopted from off-chip networks. As a result, the on-chip network architecture will not scale properly because of design complexity. In this paper, we propose a low-cost, on-chip network router microarchitecture which is different from the commonly assumed baseline router microarchitecture. We reduce the cost of on-chip networks by partitioning the crossbar, prioritizing packets in flight to simplify arbitration, and reducing the amount of buffers. We show that by introducing intermediate buffers to decouple the routing in the x and the y dimensions, high performance can be achieved with the proposed, low-cost router microarchitecture. By removing the complexity of a baseline router microarchitecture, the low-cost router microarchitecture can also approach the ideal latency in on-chip networks. However, the prioritized switch arbitration simplifies the router but creates starvation for some nodes. We show how delaying the rate credits are returned upstream can be used to implement a distributed, starvation avoidance mechanism to provide fairness. Our evaluations show that the proposed low-cost router can reduce the area by 37% and the power consumption by 45% compared with a baseline router microarchitecture that achieves a similar throughput.