DASC cache

For many microprocessors, cache hit time determines the clock cycle. On the other hand, cache miss penalty(measured in instruction issue delays) becomes higher and higher. Conciliating low cache miss ratio with low cache hit time is an important issue. When caches are virtually indexed, the operating system (or some specific hardware) has to manage data consistency of caches and memory. Unfortunately, conciliating physical indexing of the cache and low cache hit time is very difficult. In this paper, we propose the Direct-mapped Access Set-associative Check cache (DASC) for addressing both difficulties. On a DASC cache, the cache array is direct-mapped, so the cache hit time is low. However the tag array is set-associative and the external miss ratio on a DASC cache is the same as the miss ratio on a set-associative cache. When the size of an associativity degree of the tag array is tied to the minimum page size, a virtually indexed but physically tagged DASC cache correctly handles all difficulties associated with cache consistency. Trace driven simulations show that, for cache sizes in the range of 16 to 64 Kbytes and for page sizes in the range 4 to 8 Kbytes, a DASC cache is a valuable trade-off allowing fast cache hit time and low cache miss ratio while cache consistency management is performed by hardware