Two-level ata prefetching

Data prefetching has been shown to be an effective tool in hiding part of the latency associated with cache misses in modern processors. Traditionally, data prefetchers fetch data into a small prefetch buffer near the LI for low latency, or the L2 cache for greater coverage and less cache pollution. However, with the L1-L2 cache speed gap growing, significant performance gains can be obtained if the data pref etcher can operate as aggressively as an L2-level pref etcher but with the fast hit times of an LI-level pref etcher. In this paper, we propose a prefetching framework where an LI-level prefetcher and an L2- level prefetcher work cooperatively to reduce the average access time more than either one alone can. We evaluate several design alternatives suited to perform synergistically under different workloads. From the insight we gather from this analysis, we propose a confidence-based adaptive prefetcher that can improve prefetch efficiency significantly with judicious use of available bus bandwidth. Our results show that for certain prefetcher combinations, two- level prefetching can achieve the cumulative speedup attained from either prefetcher alone. Furthermore, when compared to other two-level prefetching models, the adaptive design provides similar speedups with appreciably less bus traffic.