•In real life, applications are interrupted and some
other program runs for a while (if only
the OS)
•This means the branch prediction is regularly
trashed
•Simple predictors re-learn fast
–in 2-bit bimodal predictor, all executions of given
branch update same 2 bits
•Sophisticated predictors re-learn more slowly
–for example, in (2,2) gselect predictor, prediction
updates are spread across 4
BHTs
•Selective predictor may choose fast learner predictor until better predictor warms up
•