Unbalanced cache systems

Abstract

The new concept of an unbalanced, hierarchically-divided cache memory system is introduced and analyzed. This approach generalizes existing cache structures by allowing different memory references (e.g. as possibly unevenly divided within an address-space) to be subject to various levels of caching as well as varied amounts of cache at each level. Under the assumption that the total cache size at a particular level is fixed, it is easily shown that at least one divided cache structure exists for which the miss-rate is the same as a single unified cache. By using alternate implementations, however, the method may provide a significant decrease in miss-rates as is shown via simulations. Specifically, SPEC95 benchmarks are used to demonstrate that the technique is effective for general usage but it may be even more useful for embedded systems where memory access patterns can be more fully controlled (i.e. via the compiler). In addition to improved miss-rates, another advantage is that the hit-time for multiple smaller caches may be smaller than for a single larger cache. Disadvantageous, but readily surmountable, electrical aspects are also discussed.