The Role of Adaptivity in Two-level Adaptive Branch Prediction
Stuart Sechrest, Chih-Chieh Lee, Trevor N. Mudge
Abstract
Seeking higher branch prediction accuracy, architects are making use of
the extended history of individual branches. One approach is to divide
the branch prediction task into two levels, the first records the
results of previous branches, the second makes predictions based upon
previous instances in which particular patterns arose. Current
two-level schemes use simple state machines in this second level to
provide adaptive predictions. We demonstrate that the predictions in
this second level can be made statically with performance that is
competitive with adaptive schemes. Further we provide a simple
algorithm for devising these predictions. This fixed scheme makes
errors in a way that matches the errors made by adaptive schemes,
providing insight into the workings of adaptive two-level schemes.
Keywords
dynamic branch prediction, two-level branch prediction
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