Advanced Computer Architecture, Imperial College 2001
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Prediction pay-off
•Prediction pay-off matrix shows costs of false negatives and false positives
PNAN
True negative
PNAT
false negative
Predicted
not-taken
PTAN
false positive
PTAT
true positive
Cube: Predicted taken
Predicted
taken
Actually
not-taken
Actually
taken
Actual branch delay is
PPTAT*CPTAT +
PPNAT*CPNAT +
PPTAN*CPTAN +
PPNAN*CPNAN
Asymmetry: is it better to have a false negative, or a false positive?