Errors Implementing Hybrid Branch Predictors on RISCV BOOM core

[Ogbo0810]

I am working on implementing hybrid branch predictors listed below

• Gshare + TAGE
• TAGE + Alpha
• Perceptron + TAGE
• Gshare + Alpha
• Perceptron + Gshare
• Perceptron + Alpha
• Perceptron + TAGE + Alpha
  I created a class definition of the hybrid predictor in the config-mixins.scala file and create a class instance in the BOOMConfigs.scala file.
  When I try doing that, the results I get are the same as if I run the benchmark programs (multiplication.riscv, qsort.riscv, and dhrystone.riscv) without any branch predictor.

These are screenshots of what I did for the Gshare + TAGE hybrid combination.

The idea is to replace tagless base predictor (PC indexed 2-bit counter bimodal table) of TAGE with Gshare

Class Definition of Hybrid combination of Gshare and Tage in config-mixins.scala file

Class instance of Hybrid combination of Gshare and Tage in BOOMConfigs.scala file

The CPI I get for all three benchmark programs (multiplication.riscv, qsort.riscv, and dhrystone.riscv) with this hybrid combination is the same as the CPI for when I run the same benchmark programs with no branch predictor.

[jerryz123]

Reorder WithHybridGshareTAGE above WithNSmallBooms

[Ogbo0810]

Thank you for your recommendation @jerryz123.
I reordered it as you suggested but I am still having the same results as before.

I would appreciate any further suggestions.

[jerryz123]

No, I mean in this class:

, reorder them

[Ogbo0810]

Hi @jerryz123
I reordered it as you recommended as follows:

I run into an error when I evaluate with multiplication.riscv benchmark

[Ogbo0810]

@jerryz123
I also reordered it as follows:

I still have this error:

[jerryz123]

Can you show the full stack trace? Not just the end?

[Ogbo0810]

Hi @jerryz123

I has the stacktrace as follows:

[jerryz123]

I think you have to increase bpdMaxMetaLength in your predictor config.

[Ogbo0810]

Hi @jerryz123
I increased it as you recommended and I am able to get improved results as I aimed for.
Thank you very much. I really appreciate your help