Ordering circuit establishment in multiplane NoCs

Abstract

Segregating networks-on-chips (NoCs) into data and control planes yields several opportunities for improving power and performance in chip-multiprocessor systems (CMPs). This article describes a hybrid packet/circuit switched multiplane network optimized to reduce latency in order to improve system performance and/or reduce system energy. Unlike traditional circuit preallocation techniques which require timestamps to reserve circuit resources, this article proposes an order-based preallocation scheme . By enforcing the order in which resources are scheduled and utilized rather than a fixed time, the NoC can take advantage of messages that arrive early while naturally tolerating message delays due to contention. Ordered circuit establishment is presented using two techniques. First, Déjà Vu switching preestablishes circuits for data messages once a cache hit is detected and prior to the requested data becoming available. Second, using Red Carpet Routing , circuits are proactively reserved for a return data message as a request message traverses the NoC. The reduced communication latency over configured circuits enable system performance improvement or saving NoC energy by reducing voltage and frequency without sacrificing performance. In simulations of 16 and 64 core CMPs, Déjà Vu switching enabled average NoC energy savings of 43% and 53% respectively. On the other hand, simulations of communication sensitive benchmarks using Red Carpet Routing show speedup in execution time of up to 16%, with an average of 10% over a purely packet switched NoC and an average of 8% over preconfiguring circuits using Déjà Vu switching .