Rerouting: Scalable NoC self-optimization by distributed hardware-based connection reallocation

Networks-on-Chip (NoC) are the most promising candidates for scalable communication infrastructures in manycore architectures. To ensure scalability, distributed management of communication resources needs to replace centralized approaches. Hence, distributed adaptive routing schemes in combination with selection strategies are used to take semi-optimal routing decisions according to the current NoC utilization. Once these routing decisions are taken for guaranteed service connections, which are established for longer periods, the load situation can change during their lifetime. For such connections taken routing decisions might be poor at a later point in time due to dynamically changing communication workload. The proposed hardware-based mechanism called rerouting reacts on changing load conditions and reallocates existing connections transparently. This balances the NoC load and allows to increase the number of guaranteed service connections. Throughput and delay of existing connections can also be improved by rerouting. The concept is investigated using synthetic traffic patterns and distributed video processing applications. ASIC and FPGA synthesis results are presented to investigate the implementation costs.