Contention Alleviation in Network-on-Chips

In a network-on-chip (NoC) based system, the NoC is a shared resource among multiple processor cores. Requests generated by different applications running on different cores can create severe contention in NoCs. This contention can jeopardize the system performance and power efficiency in many different formats. First and foremost, we discover that the contention in NoCs can induce inter-application interference, leading to overall system performance degradation, prevent fair-progress of different applications, and cause starvation of unfairly-treated applications. We propose the NoC Application Slowdown (NAS) Model, the first online model that accurately estimates how much network delays due to interference contribute to the overall stall time of each application. We use NAS to develop Fairness-Aware Source Throttling (FAST), a mechanism that employs slowdown predictions to control the network injection rates of applications in a way that minimizes system unfairness. Furthermore, although removing buffers from the constituent routers can reduce power consumption and hardware complexity, the bufferless NoC is subject to the growing deflection caused by contention, leading to severe performance degradation and squandering power-saving potential. we then propose Deflection Containment (DeC) for the bufferless NoC to address its notorious shortcoming of excessive deflection for performance improvement and power reduction. With a link added to each router for bridging subnetworks (whose aggregated link width equals a give value, say, 128b), DeC lets a contending flit in one subnetwork be forwarded to another subnetwork instead of deflected, yielding extraordinary deflection reduction and greatly enriching path diversity. In addition, router microarchitecture under DeC is rectified to shorten the critical path and lift network bandwidth. Last but not least, beside 1-to-1 flow, the growing core counts urgently requires effective hardware support to alleviate the contention caused by 1-to-many and many-to-1 flow. We propose Carpool, the very first bufferless NoC optimized for 1-to-many and many-to-1 traffic. Carpool adaptively forks new flit replicas and performs traffic aggregation at appropriate intermediate routers to lessen bandwidth demands and reduce contention. We propose the microarchitecture of Carpool routers and develop parallel port allocation which supports multicast and reduces critical paths to improve network bandwidth