Do we need wide flits in Networks-on-Chip?

Packet-based Networks-on-Chip (NoC) have emerged as the most viable candidates for the interconnect backbone of future Chip Multi-Processors (CMP). The flit size (or width) is one of the fundamental design parameters within a NoC router, which affects both the performance and the cost of the network. Most studies pertaining to the NoC of general-purpose microprocessors adopt a certain flit width without any reasoning or explanation. In fact, it is not easy to pinpoint an optimal flit size, because the flit size is intricately intertwined with various aspects of the system. This paper aims to provide a guideline on how to choose an appropriate flit width. It will be demonstrated that arbitrarily choosing a flit width without proper investigation may have serious repercussions on the overall behavior of the system.