Benefits of Selective Packet Discard in Networks-on-Chip

Today, Network on Chip concepts principally assume inherent lossless operation. Considering that future nanometer CMOS technologies will witness increased sensitivity to all forms of manufacturing and environmental variations (e. g., IR drop, soft errors due to radiation, transient temperature induced timing problems, device aging), efforts to cope with data corruption or packet loss will be unavoidable. Possible counter measures against packet loss are the extension of flits with ECC or the introduction of error detection with retransmission. We propose to make use of the perceived deficiency of packet loss as a feature. By selectively discarding stuck packets in the NoC, a proven practice in computer networks, all types of deadlocks can be resolved. This is especially advantageous for solving the problem of message-dependent deadlocks, which otherwise leads to high costs either in terms of throughput or chip area. Strict ordering, the most popular approach to this problem, results in a significant buffer overhead and a more complex router architecture. In addition, we will show that eliminating local network congestions by selectively discarding individual packets also can improve the effective throughput of the network. The end-to-end retransmission mechanism required for the reliable communication, then also provides lossless communication for the cores.