8 - Dynamic Branch Prediction

8 - Dynamic Branch Prediction - Dynamic Branch Prediction...

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Dynamic Branch Prediction The effectiveness of a branch prediction scheme depends on The accuracy The cost of a branch when the prediction is correct and when the prediction is incorrect. Performance = ƒ(accuracy, cost of misprediction) These branch penalties depend on the structure of the pipeline, the type of predictor, and the strategies used for recovering from misprediction. The simplest dynamic branch-prediction scheme is a branch-prediction buffer or branch history table. head2right It is a small memory indexed by the lower portion of the address of the branch instruction head2right it has no tags and is useful only to reduce the branch delay when it is longer than the time to compute the possible target PCs. head2right If the hint turns out to be wrong, the prediction bit is inverted and stored back.
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Branch History Table is simplest –Lower bits of PC address index table of 1-bit value –Says whether or not branch taken last time –No address check
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