About Branch Prediction of i7

Question

I want to know how Intel i7 processor's branch prediction works?

Currenly, I know the predictor called "dynamic branch prediction".

For 1-bit predictor: The hardware always predicts a branch instruction to take the same direction it took the last time it was executed.

A refined version working better in practice is the 2-bit predictor. In order to further improve the prediction accuracy, 2-bit prediction schemes were introduced. In these schemes the prediction must be wrong twice before it is changed.

Does i7 have the same predictor as the above?

Answer 1

Most of what we know about the branch predictor comes from testing. Intel has not released much in the way of details. The misprediction penalty is about 18 clock cycles, so accurate branch prediction is important.

Intel uses a two level branch predictor. The inner level is believed to be unchanged from the Core 2 CPUs.

The outer level is more sophisticated and can even correctly predict loops with fixed counts up to 64. Two 18-bit global history buffers are used. One contains all jumps that have been taken at least once. The other contains the most important jumps. (The number of entries in these buffers is unknown.)

Note that indirect jumps and calls have their own predictor.