HSR: Hierarchical Source Routing Model for Network-on-Chip

Distributed Routing Model (DRM) and Centralized Routing Model (CRM) are two mainstream routing models for Network-on-Chip (NoC). DRM is scalable and efficient, but its state learning is costly because exchanging network state must be in flooding form which may consume large amount of bandwidth. CRM monitors and send real-time network state to a central routing node as the basis of routing path computing which can achieve the optimal routing decision for each packet but suffers from huge design complexity and non-scalability. In this work, we propose a novel routing model called Hierarchical Source Routing (HSR) in which a tree-like hierarchical control network is built above the original network. Each non-leaf node in the tree is regarded as a control node that manages the network states and routing decisions of a group of node in the lower level. We propose two state update modes of the non-leaf nodes named HSR-PATH and HSR-PORT, which applies the average minimum path load and weighted port load respectively for the efficacy of optimal path calculation. Their implementation and overhead are also discussed. Our experiment shows that HSR-PATH and HSR-PORT outperform DRM in terms of Saturated Injection Rate by 26.1% and 17.9% on average respectively, and achieves 96.6% performance compared with CRM with much less power consumption. Finally, we use Throughput Energy Ratio (TER) as the comprehensive indicator and HSR-PATH and HSR-PORT outperform CRM by 59.4% and 13.4% respectively and DRM by 13.7% and 17.3% respectively in terms of TER.