Helia: Heterogeneous Interconnect for Low Resolution Cache Access in snoop-based chip multiprocessors

Abstract

In this work we introduce Heterogeneous Interconnect for Low Resolution Cache Access (Helia). Helia improves energy efficiency in snoop-based chip multiprocessors as it eliminates unnecessary activities in both interconnect and cache. This is achieved by using innovative snoop filtering mechanisms coupled with wire management techniques. Our optimizations rely on the observation that a high percentage of cache mismatches could be detected by utilizing a small subset but highly informative portion of the tag bits. Helia relies on the snoop controller to detect possible remote tag mismatches prior to tag array lookup. Power is reduced as a) our wire management techniques permit slow transmission of a subset of tag bits while tag mismatches are being detected and b) we avoid cache access for mismatches detected at the snoop controller. Our Evaluation shows that Helia reduces power in interconnect (dynamic: 64% to 75%, static: 45% to 50%) and cache tag array (dynamic: 57% to 58%, static: 80%) while improving average performance up to 4.4%.