Fine-grain update control protocol for a distributed shared memory system

The paper proposes a new coherence protocol for a distributed shared memory (DSM) system, called the Selective Validity Control (SVC) protocol. There are two main obstacles that degrade the performance of a DSM system as follows: (1) it is difficult to hide access latency efficiently; (2) the excessive amount of unnecessary coherence traffic is generated. The SVC protocol is the coherence protocol that alleviates these problems by introducing fine-grain control of data transfer. The SVC protocol can also promote and improve the effectiveness of the prefetch operation by allowing cache lines to have partially valid/invalid states. The paper discusses the major problems of a conventional DSM system, and describes the design, characteristics, and primitives of the SVC protocol in detail. To evaluate the performance of the SVC protocol, a trace-driven simulator has been developed. Benchmark programs such as Gauss elimination, Fibonacci, FFT, and Jacobi iteration, were executed on the simulator to measure the amount of data transferred and the number of coherent messages issued. The simulation results show that the SVC protocol can maintain the coherence with less traffic and also minimizes the number of messages required compared to the conventional protocols.