CATCH: A mechanism for dynamically detecting cache-content-duplication in instruction caches

Abstract

Cache-content-duplication (CCD) occurs when there is a miss for a block in a cache and the entire content of the missed block is already in the cache in a block with a different tag. Caches aware of content-duplication can have lower miss penalty by fetching, on a miss to a duplicate block, directly from the cache instead of accessing lower in the memory hierarchy, and can have lower miss rates by allowing only blocks with unique content to enter a cache. This work examines the potential of CCD for instruction caches. We show that CCD is a frequent phenomenon and that an idealized duplication-detection mechanism for instruction caches has the potential to increase performance of an out-of-order processor, with a 16KB, 8-way, 8 instructions per block instruction cache, often by more than 10% and up to 36%. This work also proposes CATCH, a hardware mechanism for dynamically detecting CCD for instruction caches. Experimental results for an out-of-order processor show that a duplication-detection mechanism with a 1.38KB cost captureson average 58% of the CCD's idealized potential. © 2011 ACM.