Research On Congestion Control Technology For Network-on-Chip

Network-on-Chip (NoC) represents a scalable solution to on-chip communication of complex SoC, but congestion severely affects the overall performance of NoC. Due to the constraints of area, power consumption and hardware resources, those effective congestion control techniques used in computer network are hardly implemented in NoC. At present, the congestion control methods in NoC mainly resort to structure improvement, routing algorithm design and load regulation. However, there is a lack of integrated consideration with network structures alteration and routing algorithms improvement, and researchers are usually absorbed in performance improvement while ignore hardware overhead, which lead to issues of great complexity and high hardware overhead.Based on the analysis of existing congestion control mechanism in NoC, this dissertation presents a method combining alteration of local interconnection and improvement of routing algorithm for load balance, and a mechanism to regulate load. Furthermore, in order to improve congestion control effect and reduce the demands of buffer, a dynamic buffer allocation scheme based on data flow direction is put forward.Main work and contributions of this dissertation are outlined as follows:1. A method combining alteration of local interconnection and improvement of routing algorithm is proposed to alleviate congestion in NoC. By adjusting the structure of network interface, the communication hot-spot could connect to multiple adjacent routers with multiplexer, thus reducing the probability of congestion resulted from excessive traffic. Thereafter, a region-based XY-YX routing algorithm is presented for the adjusted NoC topology. According to the relative position between source node and destination node, this algorithm chooses the router in corresponding orientation, and adopts XY or YX routing algorithm to determine the data transmission path. The simulation results show that this method not only effectively reduces the average packet transmission delay and increases network throughput, but also makes a better trade-off between performance and hardware cost.2. Two methods based on regulation of traffic are presented for congestion control in NoC. The first string applies an end-to-end Credit-based policy to control the amount of data sent to network each time. In addition, an injection rate control algorithm with weighted proportional fairness is proposed, which uses the communication probability between nodes as weighted factor, and introduces a utility function with proportional fairness. Thus, the injection rate control is transformed into constrained optimization under buffer of destination node router, and the optimized injection rate could be gained by Lagrange Multiplier method. The simulation results show that these methods can effectively control network load and instantaneous load strength.3. A novel dynamic buffer allocation scheme based on data flow direction is proposed. In this mechanism, the concept of "group" is put forward and "group" corresponds to one and only output port. The data sent to different output ports are stored in the form of "group", and the control logic dynamic allocates buffer resources according to the data size in various "group". By monitoring the available buffering capacity, congestion control directly target specific port and the accuracy of control improve. The simulation results show that this method can effectively reduces demands of buffer resources as well as gain similar performance.