An Energy-Efficient L2 Cache Architecture Using Way Tag Information under Write-Through Policy

Many high-performance microprocessors employ cache write-through policy for performance improvement and at the same time achieving good tolerance to soft errors in on-chip caches. However, write-through policy also incurs large energy overhead due to the increased accesses to caches at the lower level (e.g., L2 caches) during write operations. In this paper, we propose a new cache architecture referred to away-tagged cache to improve the energy efficiency of write-through caches. By maintaining the way tags of L2 cache in the L1 cache during read operations, the proposed technique enables L2 cache to work in an equivalent direct-mapping manner during write hits, which account for the majority of L2 cache accesses. This leads to significant energy reduction without performance degradation. Simulation results on the SPEC CPU2000 benchmarks demonstrate that the proposed technique achieves 65.4% energy savings in L2 caches on average with only 0.02% area overhead and no performance degradation. Similar results are also obtained under different L1 and L2 cache configurations. Furthermore, the idea of way tagging can be applied to existing low-power cache design techniques to further improve energy efficiency.