An energy saving algorithm for variable cache ways

Set associative caches with variable ways extending to one additional set is proposed in literature. In this model, two sets are searched for tag match during address mapping. Assuming the cache operates in two energy modes - high power mode and low power mode, both the sets associated with address mapping are enabled in high energy mode. This paper proposes an algorithm based on principle of locality to reduce the energy consumption. The last access to set among the two possible choices is chosen as the set to access during current access to a set. If the line is found in the set, it is accessed. If the line is absent, the other set associated with the mapped set is accessed for match. If it is a hit, the line is accessed. If it is a miss, the line is placed in vacant way if available. In case the set and associated set is full, the least recently used way in the mapped set is replaced. The proposed algorithm is simulated with SPEC2K benchmarks. An improvement of 79% in energy is observed with 9% improvement in AMAT.