The Dirty-Block Index

On-chip caches maintain multiple pieces of metadata about each cached block—e.g., dirty bit, coherence information, ECC. Traditionally, such metadata for each block is stored in the corresponding tag entry in the tag store. While this approach is simple to implement and scalable, it necessitates a full tag store lookup for any metadata query—resulting in high latency and energy consumption. We Vnd that this approach is inefficient and inhibits several cache optimizations.