Virtual Hierarchies

Memory system hierarchies are fundamental to computing systems. They have long improved performance because most programs temporally concentrate accesses to code and data. However, emerging many-core Chip MultiProcessors (CMPs) provide a new computing landscape. Rather than just time-sharing jobs on one or a few cores, the authors expect abundant cores will encourage a greater use of space sharing, where single-threaded or multithreaded jobs are simultaneously assigned to separate groups of cores for long time intervals. To optimize for space-shared workloads, they propose using virtual hierarchies to overlay a coherence and caching hierarchy onto a physical system.