If I want to observe the prediction accuracy of different branches of O3cpu in gem5, should I modify the O3 code? If so, do I need to rebuild gem5

Question

In O3, only one algorithm, bpred_unit, is used, and gem5 also provides several other branch prediction algorithms. I want to compare the prediction accuracy of different algorithms, what should I do？Need to change the code? Need to rebuild gem5？

Answer 1

In fact, by simply checking out this site, you'll realize that the BPredUnit::lookup is a pure virtual function, implemented in

• gem5::branch_prediction::MultiperspectivePerceptron
• gem5::branch_prediction::MultiperspectivePerceptronTAGE
• gem5::branch_prediction::TAGE, gem5::branch_prediction::LocalBP,
• gem5::branch_prediction::TournamentBP, and
• gem5::branch_prediction::BiModeBP.

The default BP is TournamentBP, you can check in m5out/config.ini [system.cpu.branchPred]

However, you can modify the option in the command line. For example "--bp-type=BiModeBP" will change the BP to BiModeBP.