Performance Evaluation of Hierarchical-Torus NoC

Torus is gaining a great interest in on-chip networks, and to further reduce torus diameter, hierarchical-torus networks have been proposed, where a cluster of IPs are connected by a single router. This paper investigates the performance merits of clustering in the torus, and compares the performance of the hierarchical-torus to that of the torus. Our simulation results show that, although hierarchical-torus has lower network diameter than the tours, the latter provides better latency performance. Hierarchical-torus suffers from the high load of traffic distributed on fewer channels, compared to the torus, resulting in high message blocking delays. Hierarchical-torus manages to outperform the torus only under local traffic distribution or when the fraction of hot-spot traffic is very large. Also, our results show hierarchical-torus greatly improves its performance in terms of message latency under deterministic routing with a small number of virtual channels, a performance which is almost similar to that obtained when messages are adaptive routed.