branch_predictor

A simple gshare branch predictor writting in Vlang. It is really fast than a C version!

What is this ?

Branch predictor is one of the most import circuit in modern super scalar CPUs. By given a PC, the predictor should provide a suggestion of Taken or Not Taken.

This project provide a branch predictor simualtion framework, which is written in vlang. To demo, it provide a simple gshare implementation of branch predictor.

Also provide some branch instruction traces, which is converted from CBP-16 traces.

How to run ?

You must install zstd in your system:

  apt install libzstd-dev

The project use the cbsl, which need the zstd compress library to work.

  $ git clone https://github.com/kbkpbot/branch_predictor.git
  $ cd branch_predictor
  $ git submodule update --init --recursive
  $ v -prod .
  $ ./branch_predictor

Provided with no args, the branch_predictor will try to read the content of traces/TRACE_LIST.txt, which provide a trace list , one trace per line. You can comment out some traces by a leading '#', like this:

#LONG_MOBILE-1
#LONG_MOBILE-2
LONG_MOBILE-3
LONG_MOBILE-4
SHORT_MOBILE-1
SHORT_MOBILE-2
SHORT_MOBILE-3
SHORT_MOBILE-4
SHORT_MOBILE-24
SHORT_MOBILE-25
SHORT_MOBILE-27
SHORT_MOBILE-28
SHORT_MOBILE-30

You should get result something like this:

====================Summary====================
traces/LONG_MOBILE-1            = 0.556903
traces/LONG_MOBILE-2            = 1.388763
traces/LONG_MOBILE-3            = 7.812431
traces/LONG_MOBILE-4            = 0.006016
traces/SHORT_MOBILE-1           = 2.933743
traces/SHORT_MOBILE-2           = 11.394828
traces/SHORT_MOBILE-24          = 0.000489
traces/SHORT_MOBILE-25          = 0.001764
traces/SHORT_MOBILE-27          = 0.480042
traces/SHORT_MOBILE-28          = 0.007541
traces/SHORT_MOBILE-3           = 3.752000
traces/SHORT_MOBILE-30          = 6.294661
traces/SHORT_MOBILE-4           = 5.163341
===============================================
Total MISPRED_PER_1K_INST               = 39.8

Score = 86(39.8) time cost = 2.94 seconds

MISPRED_PER_1K_INST mean Miss Predictions Per 1000 Instructions.

How to writing my own predictor?

Just modify the predictor.v. You target is try to min the MISPRED_PER_1K_INST.

A C verion of this branch predictor?

Yes, we provide a C version.

  $ make
  $ ./predictor

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