Improving cache performance with Full-Map Block Directory

There are two concurrent paths in a typical cache access — one through the data array and the other through the tag array. In most cases, the path through the tag array is significantly longer than that through the data array. In this paper, we propose a new scheme that exploits this imbalance in the tag and data paths to improve overall cache performance. Under this scheme, an additional tag directory, the Full-Map Block Directory, is used to provide an alternate tag path to speed up cache access for almost all the memory requests. This scheme is based on the observation that spatial locality exists on a cache line basis, i.e., cache lines near one another tend to be referenced together. Performance evaluation using a TPC-C-like benchmark and selected applications from the SPEC92 benchmark suite demonstrates that this scheme has the potential to improve overall system performance by more than 20%.