1.3.2 Dynamically Ordered Cache Probes
In contrast to the static schemes, researchers have developed schemes which redirect the first probe to a predicted location. The MRU cache design keeps the MRU information associated to each set. When searching for data, the block indicated by the MRU bit is probed. However the MRU bits must be fetched prior to accessing the cache. The PSA (Predictive Sequential Associative) cache design moves the prediction procedure to previous stages of pipelining so that the MRU information is presented to the cache simultaneously with the memory reference. The Reactive- Associative Cache design moves most active blocks to direct- mapped positions and reactively displaces only conflicting blocks based on the PSA cache design. It reduces cache assess latency at the cost of higher miss rates and larger power consumption. Dropsho [15] discussed an accounting cache architecture. The accounting cache first accesses part of the ways of a set associative cache, known as a primary access. If there is a miss, then the cache accesses the other ways, known as a secondary access. A swap be- tween the primary and secondary accesses is needed when there is a miss in the primary and a hit in the secondary access. Energy is saved on a hit during the primary access. Way-prediction was first proposed to reduce the cache access latency. The power efficiency of way-prediction techniques were discussed later.