Channel borrowing: an energy-efficient nanophotonic crossbar architecture with light-weight arbitration

The emerging on-chip optical interconnection has become a promising candidate for future network design because of its advantages in high bandwidth density, low propagation delay and dynamic power consumption. However, a key challenge of on-chip optics is the high static power consumption which dominates the total network power. Hence, it is imperative to design an energy-efficient optical network architecture with high throughput while consuming low static power. In conventional optical crossbars, static channel allocation results in low channel utilization and network throughput, while full channel sharing requires a significant number of microrings, which incurs high static power. To obtain high network throughput with low power consumption, this paper proposes a nanophotonic crossbar architecture with light-weight distributed arbitration. Network channels are allocated to an owner node, but can also be used by a few other nodes during idle time. The number of microring resonators is greatly reduced compared to the full channel sharing architecture. The arbitration is also simplified due to the small number of nodes sharing a channel. Every node can use the statically assigned channel to avoid starvation and borrow an additional idle channel to improve the utilization of the network. We intelligently select the network nodes that should share a channel to increase the chance of successful borrowing with low probability of conflict. The energy efficiency of the proposed network architecture is evaluated in terms of energy efficiency (throughput/watt) and Energy-delay2(ED2) using synthetic traces and traffic traces from PARSEC benchmarks. The simulation results show that our design can improve energy efficiency by 34% and 26% and improve ED^2 by 73% and 45% compared to Single-write-multi-read (SWMR) crossbars and Multi-write-multi-read (MWMR) crossbars respectively.

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