Dynamic associative caches: Reducing dynamic energy of first level caches

We propose Dynamic Associative Cache (DAC) - a low complexity design to improve the energy-efficiency of the data caches with negligible performance overhead. The key idea of DAC is to perform dynamic adaptation of cache associativity - switching the cache operation between direct-mapped and set-associative regimes - during the program execution. To monitor the program needs in terms of cache associativity, the DAC design employs a subset of shadow tags: when the main cache operates in the set-associative mode, the shadow tags operate in the direct-mapped mode and vice versa. The difference in the hit rates between the main tags and the shadow tags is used as an indicator for the cache mode switching. We show that DAC performs most of its accesses in the direct-mapped mode resulting in significant energy savings, at the same time maintaining performance close to that of set-associative L1 D-cache.