Express Virtual Channels with Taps (EVC-T): A Flow Control Technique for Network-on-Chip (NoC) in Manycore Systems

Abstract—Manycore systems require energy-efficient on-chip networks that provide high throughput and low latency. The performance of these on-chip networks affects cache access latency and, consequently, system performance. This paper proposes solutions to address the performance limitations related to the use of snoop-based cache coherence protocol on switched network-on-chip (NoC). We propose a new network flow control technique, Express Virtual Channel with Taps (EVC-T), for transmitting both broadcast packets and data packets efficiently. In addition, we propose a low-latency broad-cast packet notification tree network that maintains the order of broadcast packets on an unordered NoC. We evaluate our technique using both synthetic traffic and parallel benchmark suites through detailed system simulation. EVC-T reduces the average network latency by 24 % with a negligible change in power for synthetic benchmarks. For NAS parallel applications, EVC-T increases the instructions per cycle (IPC) by 9 % on average with minimal increase in power. Our technique reduces the energy-delay product (EDP) by 13 % on average across all benchmarks. Keywords-Express virtual channel with taps; Manycore sys-tems; NoC; Simulation; Snoop based cache coherence. I