Costs and benefits of flexibility in spatial division circuit switched networks-on-chip

Abstract

Although most Network-on-Chip (NoC) designs are based on Packet Switching (PS), the importance of Circuit Switching (CS) should not be underestimated. Many MPSoC executing real-time applications require an underlying communication backbone that can relay messages from one node to another with guaranteed throughput. Compared to PS, CS can provide guaranteed throughput with lower area and power overheads. It is also highly suited for applications where nodes transfer long messages. Spatial Division Multiplexing (SDM) can allow more efficient use of available network resources by dividing them among multiple simultaneous transactions. The network developed by Vali [1] has three design variations based on the number of sub-channels, has a predictable connection setup time, and uses CS to provide guaranteed throughput once a connection is established. In this paper we use this network as a basis to study the effect of flexibility based on SDM, on the performance of a CS networks. A network evaluation platform has been developed to configure and evaluate networks with a maximum of 8 sub-networks, with each subnetwork comprising of 1, 2 or 4 sub-channels. We show that under uniform traffic pattern with requests of uniform random bandwidth (BW) requirement, a less flexible network outperforms a network with higher flexibility due to a phenomenon we call 'stray requests'. We conclude this paper by showing that under high network traffic, performance of our flexible networks can be as much as 113% better than HAGAR [2] and Liu's [3] network.