cpu: Tune BTBTAGE table sizes

[CJ362ff]

Change-Id: Icc7c697cdd5a322b557fe1fe2860deed54a1ca40

Summary by CodeRabbit

• Chores
  • Optimized branch prediction subsystem parameters to enhance system performance efficiency.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 25fa5dc2-b01c-4f4a-99b3-c9c6fbd9633b

📥 Commits

Reviewing files that changed from the base of the PR and between 6a7b769 and cb07c95.

📒 Files selected for processing (1)

• src/cpu/pred/BranchPredictor.py

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📝 Walkthrough

Walkthrough

This PR modifies BTBTAGE predictor per-table configuration in BranchPredictor.py, adjusting table sizes from uniform 2048 entries to a varied pattern and updating tag bit widths for the last two TAGE tables from 13 to 15 bits.

Changes

Cohort / File(s)	Summary
BTBTAGE Configuration src/cpu/pred/BranchPredictor.py	Updated per-table tableSizes array to vary table capacities (4th table increased to 4096, last two reduced to 1024) and increased TTagBitSizes for the last two tables from 13 to 15 bits.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• Revert "cpu-o3: Refactor numWays to support per-table configuration" #795: Modifies BTBTAGE's per-table configuration parameters (tableSizes and TTagBitSizes) in the same predictor.
• Restore/per table numways #798: Introduces per-table vectorized parameters (numWays and tableSizes) for BTBTAGE predictor configuration.
• Tage tunning and L3 Cache size change #812: Modifies TAGE predictor sizing parameters (tableSizes/numWays) in branch predictor configuration.

Suggested labels

perf, align-kmhv3

Suggested reviewers

• jensen-yan

Poem

🐰 Hop hop, the tables tune their stride,
Four grows wide, the last ones shrink with pride,
Tags reach fifteen, deeper eyes they see,
Branch paths faster, predictive harmony!

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'cpu: Tune BTBTAGE table sizes' directly and accurately describes the main change: adjusting BTBTAGE predictor table configuration parameters.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch btb-t6t7-1k-tag15-align

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[github-actions]

🚀 Coremark Smoke Test Results

Branch	IPC	Change
Base (xs-dev)	2.3051	-
This PR	2.3190	📈 +0.0139 (+0.60%)

✅ Difftest smoke test passed!

[XiangShanRobot]

[Generated by GEM5 Performance Robot]
commit: cb07c95
workflow: gem5 Align BTB Performance Test(0.3c)

Align BTB Performance

Overall Score

	PR	Master	Diff(%)
Score	18.74	18.71	+0.19 🟢