RARR: Reverse Anchored Round-Robin for Link Scheduling in Network-on-Chip

As a packet is distributed along its path in a wormhole network-on-chip (NoC), the individual link schedulers can hardly fulfill packet-based allocation without synchronization, to achieve lower average latency than flit-based one does. Reverse anchored round-robin (RARR) is proposed as hybrid of flit and packet based schemes. The unique highest-priority fragment is reserved as anchor at each link and RARR attempts to synchronize by anchoring all fragments belong to the same packet. If done, the packet may be delivered continuously, i.e. at packet-level. Otherwise flit-based allocation is employed to ensure link utility and get rid of starvation. Inspired by anchored round-robin (ARR), RARR employs more deterministic anchoring scheme and eliminates deadlock in it. Popular round-robins were evaluated on a cycle-accurate simulator. RARR was shown to achieve the lowest average latency among the candidates, and outperform FFRR by more than 10% consistently.