The Cache Group Scheme for Hardware-Controlled Cache Coherence and the General Need for Hardware Coherence Control in Large-Scale Multiprocessors [Thesis]
Joseph E. Hoag · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2024
A scheme that employs cache grouping and incomplete directory state in order to reduce the cost of maintaining directory state is introduced. This thesis discusses the cache grouping scheme, describes the protocols necessary for its implementation, and gives the results of detailed simulations of the scheme using various application codes. The effects of changing cache group size and using sophisticated multicast and combination features in the interconnect are explored. It is discovered that the cache grouping scheme can equal the performance of full-directory schemes, while costing much less. The system is relatively insensitive to cache group size. Advanced multicast and combination features in the network best when used together, and have especially beneficial effect for codes that exhibit a high rate of one-to-many invalidates. The simulation of a machine employing the cache grouping scheme indicates significant performance gains over an identical machine without a shared data cache. We also discuss the time and coding required to coax efficiency out of codes run on large scale parallel machines without hardware coherent cache mechanisms.