Accurately Modeling a Photonic NoC in a Detailed CMP Simulation Framework

Photonic interconnects are a promising solution for the so-called communication bottleneck in current Chip Multiprocessor (CMPs) architectures. This technology presents an inherent low-latency and power consumption almost independent of communication distance, which are really desirable features in future Networks on Chip for next CMPs generations. However, since nanophotonic technology is still growing and therefore in an immature state, current simulators of detailed systems may not provide accurate models of photonic components. In this context, non-representative results are obtained when unaccurate photonic models are assumed.

This paper summarizes all of the components that conform a fully operative photonic NoC and presents their current state of the art. Moreover, we evaluate a realistic photonic network that consists of two photonic rings and a token-based arbitration mechanism and compare it against a non-realistic model. In addition, both realistic and non-realistic schemes are evaluated under different  configurations varying the number of wavelengths that photonic waveguides employ. The experimental results show that the non-realistic NoC presents up to 6× network latency deviation with respect to the accurate model. This deviation is translated into a performance deviation higher than 10% in several applications studied, which demonstrates the importance of accurate models when simulating current technologies under development like nanophotonics.

Finally, a power consumption model of the realistic photonic network is presented. The results show that the overall photonic network power consumption grows with the number of wavelengths per waveguide since the number of required modulators and receivers becomes higher. In this way, the proposed realistic photonic network, which employs only two wavelengths for arbitration and destination selection tasks, increases its power consumption up to 3%, so network designs with more complex arbitration mechanisms must take into account the impact of the number of wavelengths on the power consumption.