The ZCache: Decoupling Ways and Associativity

The ever-increasing importance of main memory latency and bandwidth is pushing CMPs towards caches with higher capacity and associativity. Associativity is typically improved by increasing the number of ways. This reduces conflict misses, but increases hit latency and energy, placing a stringent trade-off on cache design. We present the zcache, a cache design that allows much higher associativity than the number of physical ways (e.g. a 64-associative cache with 4 ways). The zcache draws on previous research on skew-associative caches and cuckoo hashing. Hits, the common case, require a single lookup, incurring the latency and energy costs of a cache with a very low number of ways. On a miss, additional tag lookups happen off the critical path, yielding an arbitrarily large number of replacement candidates for the incoming block. Unlike conventional designs, the zcache provides associativity by increasing the number of replacement candidates, but not the number of cache ways. To unders...

• Type: Journal
• Year: 2010
• Where: MICRO
• Authors: Daniel Sanchez, Christos Kozyrakis
• Keywords: Associativity, Cache, Hardware, MICRO 2010, Replacement Candidates