Express Link Placement for NoC-Based Many-Core Platforms

Abstract

With the integration of up to hundreds of cores in recent general-purpose processors that can be used in parallel processing systems, it is critical to design scalable and low-latency networks-on-chip (NoCs) to support various on-chip communications. An effective way to reduce on-chip latency and improve network scalability is to add express links between pairs of non-adjacent routers. However, increasing the number of express links may result in smaller bandwidth per link due to the limited total bisection bandwidth on chip, thus leading to higher serialization latency of packets in the network. Unlike previous works on application-specific designs or on fixed placement of express links, this paper aims at finding effective placement of express links for general-purpose processors considering all the possible placement options. We formulate the problem mathematically and propose an efficient algorithm that utilizes an initial solution generation heuristic and enhanced candidate generator in simulated annealing. Evaluation on 4x4, 8x8 and 16x16 networks using multi-threaded PARSEC benchmarks and various synthetic traffic patterns shows significant reduction of average packet latency over previous works.