Adaptive Caches: Effective Shaping of Cache Behavior to Workloads

We present and evaluate the idea of adaptive processor cache management. Specifically, we describe a novel and general scheme by which we can combine any two cache management algorithms (e.g., LRU, LFU, FIFO, Random) and adaptively switch between them, closely tracking the locality characteristics of a given program. The scheme is inspired by recent work in virtual memory management at the operating system level, which has shown that it is possible to adapt over two replacement policies to provide an aggregate policy that always performs within a constant factor of the better component policy. A hardware implementation of adaptivity requires very simple logic but duplicate tag structures. To reduce the overhead, we use partial tags, which achieve good performance with a small hardware cost. In particular, adapting between LRU and LFU replacement policies on an 8-way 512KB L2 cache yields a 12.7% improvement in average CPI on applications that exhibit a non-negligible L2 miss ratio. Our approach increases total cache storage by 4.0%, but it still provides slightly better performance than a conventional 10-way set-associative 640KB cache which requires 25% more storage