A novel tag access scheme for low power L2 cache

Tag comparisons occupy a significant portion of cache power consumption in the highly associative cache such as L2 cache. In our work, we propose a novel tag access scheme which applies a partial tag-enhanced Bloom filter to reduce tag comparisons by detecting per-way cache misses. The proposed scheme also classifies cache data into hot and cold data and the tags of hot data are compared earlier than those of cold data exploiting the fact that most of cache hits go to hot data. In addition, the power consumption of each tag comparison can be further reduced by dividing the tag comparison into two micro-steps where a partial tag comparison is performed first and, only if the partial tag comparison gives a partial hit, then the remaining tag bits are compared. We applied the proposed scheme to an L2 cache with 10 programs from SPEC2000 and SPEC2006. Experimental results show average 23.69% and 8.58% reduction in cache energy consumption compared with the conventional serial tag-data access and the other existing methods, respectively.