申論題

1. (10%) The importance of having a good branch predictor depends on how often conditional branches are executed. Together with branch predictor accuracy, this will determine how much time is spent stalling due to mispredicted branches. In this problem, assume a 5-stage pipeline RISC processor with the breakdown of dynamic instructions into various instruction categories is as follows

Also, assume the following branch predictor accuracies:

(e)(2%) Some branch instructions are much more predictable than others. If we know that 80% of all executed branch instructions are easy-to-predict loop-back branches that are always predicted correctly, what is the accuracy of the 2-bit predictor on the remaining 20% of the branch instructions?