Partial Packet Forwarding to Improve Performance in Fully Adaptive Routing for Cache-Coherent NoCs

Abstract

In the contest of cache-coherent Networks-on-Chip (NoCs), fully adaptive routing algorithms guarantee maximum flexibility to implement power-performance, fault tolerant, thermal and Quality of Service (QoS) management policies. However, to get rid of deadlock at both protocol and network level, their implementation imposes a relevant resource increase. Moreover, their performance are inferior to the one of deterministic and partially adaptive schemes mainly due to the additional constraints imposed to the virtual channel (VC) re-use policy. This work proposes a novel flow control scheme to improve the performance of fully adaptive routing algorithms by allowing an aggressive reuse of VCs in presence of both long and short packets. Our proposal works by splitting long packets in multiple chunks and by reallocating the VCs to the chunks rather that to the entire packet. By carefully sizing each chunk to fit the available space in the reallocated, eventually not empty, VC, we are avoiding deadlocks while increasing the NoC utilization and performance. Experimental results show that our solution offers a 23.8% increase, on average, in the saturation point when compared to the best state of the art flow control scheme for fully adaptive routing algorithms. Moreover, our flow control scheme offers similar or better performance than the XY routing algorithm with the same number of resources, and we also ensure superior flexibility in the definition of the routing function.