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 re actively 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. Drop-sho 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 between
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