Bidirectional ring, an interconnection network for shared-memory multiprocessor systems

grantor: University of TorontoA bidirectional ring is proposed in this thesis as an interconnection network for shared-memory multiprocessors to improve their performance and reliability. It consists of two rings transmitting packets in opposite directions. The constituent rings are bit-parallel and use the slotted access protocol. The bidirectional ring allows a request packet to traverse one ring from a source to the destination, and the response packet to return on the other ring; hence, a request and response transaction does not require traversal of the entire ring. This transmission protocol is advantageous in exploiting the communication locality of application programs to improve their performance. The existence of two rings in the bidirectional ring improves the reliability of the system. A cache coherence protocol is proposed for shared-memory multiprocessors using the bidirectional ring interconnect. The protocol ensures sequential consistency. A reliable implementation of this protocol is also given that can handle node and link failures. The fault handling logic is concentrated in the bypass path, which is activated only after detecting a fault, hence it does not affect the normal operation of the ring. The performance of the bidirectional ring is evaluated in comparison with a hierarchy of unidirectional rings. The simulation is performed using system parameters analogous to the NUMAchine prototype. A set of applications from the SPLASH-2 benchmark suite is used for this study. The bidirectional ring shows up to 50% lower latency than the hierarchy. Its performance is less sensitive to communication patterns. Comparing the overall performance with the hierarchy, the program execution time is reduced up to 30% on the bidirectional ring. The bidirectional ring also shows a tendency to balance the network load. The utilizations of the two constituent rings has been found to be within 5% of each other. The degradation in the performance of a faulty bidirectional ring is relatively low; a maximum increase of 6% in the execution time is found for all the benchmark applications we have simulated. The faulty ring shows the same load balancing characteristic of a good ring.Ph.D