  Virtual channel flow control is the de facto choice for modern
networks-on-chip to allow better utilization of the link bandwidth through
buffering and packet switching, which are also the sources of large power
footprint and long per-hop latency. On the other hand, bandwidth can be
plentiful for parallel workloads under virtual channel flow control. Thus,
dated but simpler flow controls such as circuit switching can be utilized to
improve the energy efficiency of modern networks-on-chip. In this paper, we
propose to utilize part of the link bandwidth under circuit switching so that
part of the traffic can be transmitted bufferlessly without routing. Our
evaluations reveal that this proposal leads to a reduction of energy per flit
by up to 32% while also provides very competitive latency per flit when
compared to networks under virtual channel flow control.
