Footprint: Regulating routing adaptiveness in networks-on-chip

Abstract

Routing algorithms can improve network performance by maximizing routing adaptiveness but can be problematic in the presence of endpoint congestion. Tree-saturation is a well-known behavior caused by endpoint congestion. Adaptive routing can, however, spread the congestion and result in thick branches of the congestion tree-creating Head-of-Line (HoL) blocking and degrading performance. In this work, we identify how ignoring virtual channels (VCs) and their occupancy during adaptive routing results in congestion trees with thick branches as congestion is spread to all VCs. To address this limitation, we propose Footprint routing algorithm-a new adaptive routing algorithm that minimizes the size of the congestion tree, both in terms of the number of nodes in the congestion tree as well as branch thickness. Footprint achieves this by regulating adaptiveness by requiring packets to follow the path of prior packets to the same destination if the network is congested instead of forking a new path or VC. Thus, the congestion tree is dynamically kept as slim as possible and reduces HoL blocking or congestion spreading while maintaining high adaptivity and maximizing VC buffer utilization. We evaluate the proposed Footprint routing algorithm against other adaptive routing algorithms and our simulation results show that the network saturation throughput can be improved by up to 43% (58%) compared with the fully adaptive routing (partially adaptive routing) algorithms.