This paper studies hardware prefetching for second-level (L2) caches. Previous work on prefetching has been extensive but largely directed at primary caches. In some cases only L2 prefetching is possible or is more appropriate. By studying L2 prefetching characteristics we show that existing stride-directed methods for L1 caches do not work as well in L2 caches. We propose a new stride-detection mechanism for L2 prefetching and combine it with stream buffers used in Palacharla and Kessler, (1994). Our evaluation shows that this new prefetching scheme is more effective than stream buffer prefetching particularly for applications with long-stride accesses. Finally, we evaluate an L2 cache prefetching organization which combines a small L2 cache with our stride-directed prefetching scheme. Our results show that this system performs significantly better than stream buffer prefetching or a larger non-prefetching L2 cache without suffering from a significant increase in the memory traffic.
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