C++ Performance Engineer
Use this skill to move C++ performance work from intuition to benchmark-backed decisions.
Workflow
- Establish reproducible baseline.
- Capture compiler, flags, CPU environment, thread pinning, and dataset sizes.
- Run baseline benchmarks before changing code.
- Identify hotspot class.
- Distinguish compute, memory bandwidth, cache misses, branch mispredicts, allocations, and lock contention.
- Prioritize hotspots by end-to-end impact, not microbenchmark delta alone.
- Apply targeted optimizations.
- Use data-layout and allocation changes for memory-bound paths.
- Use algorithmic/branch simplification for compute-bound paths.
- Use lock scope reduction, sharding, or lock-free structures for contention.
- Keep each optimization isolated and benchmarked.
- Validate with benchmark comparison.
- Compare current run against baseline with explicit regression thresholds.
- Flag statistically suspicious or high-variance benchmark rows.
- Package performance handoff.
- Provide measured deltas, affected files, tradeoffs, and risks.
- Include reproducible benchmark commands.
Commands
bashpython3 scripts/compare_benchmark_json.py \ --baseline <baseline.json> \ --current <current.json> \ --metric cpu_time \ --regression-threshold 5.0
Treat non-zero exits as blocker regressions.
Output Contract
Return:
Baseline Context: compiler/env assumptions and benchmark scope.Findings: top regressions/improvements with measured deltas.Optimization Plan: exact code-level changes and expected impact.Verification: rerun commands and regression gates.Residual Risks: variance, measurement noise, or unresolved bottlenecks.
References
references/workflow.md: detailed profiling and optimization sequence.references/optimization-playbook.md: hotspot-to-technique mapping.references/signoff-template.md: concise performance report template.
Execution Rules
- Never claim performance gains without before/after measurements.
- Keep benchmark environments comparable across runs.
- Separate microbenchmark wins from end-to-end impact.
- Escalate regressions above threshold as blockers.
