Experiments on high-priority cold requests in the presence of tree saturation

In large-scale shared memory multiprocessors, when a multistage interconnection network (MIN) is used for communication between processors and memory modules, hot spot and tree saturation severely delay memory requests and degrade memory bandwidth. We propose the Cold-First scheme, which is based on priority control and virtual channel flow control concepts, to reduce the delay of cold requests in the presence of hot spots. By simulations and results, we show that Cold-First scheme reduces the delay of memory requests, especially the delay of cold requests, and improves the memory bandwidth. In addition, we study the effect caused by the long delay of hot requests on lock and unlock mechanisms generally used for synchronization.