Rust performance

Rust Performance

Rule

Measure before optimizing and preserve correctness. Prefer algorithmic improvements and allocation-aware design over clever unsafe or unreadable micro-optimizations.

Hard Stops

Stop when:

• No target metric or representative workload exists.
• Correctness tests do not protect the behavior being optimized.
• Optimization requires unsafe, public API changes, feature changes, altered semantics, custom allocators, or substantially less readable code without approval.
• Benchmark noise makes the conclusion unreliable.

Defaults

• Use Criterion for in-process benchmarks when approved or already present.
• Use hyperfine for CLI/process startup and end-to-end command benchmarks.
• Use cargo flamegraph, OS profilers, or sampling profilers for CPU hotspots.
• Use heap/alloc profiling tools appropriate to the platform when allocation behavior is the metric.
• Use tokio-console/console-subscriber during async bottleneck diagnosis when approved.
• Benchmark one change at a time and keep inputs representative.

Workflow

1. Define metric: latency, throughput, allocations, CPU, memory, binary size, startup, or tail behavior.
2. Create or run representative benchmarks and capture baseline.
3. Profile to identify bottlenecks instead of guessing.
4. Make one focused change.
5. Rerun benchmarks enough times to compare reliably.
6. Run correctness tests, Clippy, and just check.

Antipatterns

• Optimizing code outside the measured hot path.
• Adding unsafe for avoidable zero-copy tricks.
• Cloning less by making APIs painful or unsound.
• Unbounded concurrency to improve happy-path throughput.
• Choosing Actix/Fiber-style framework equivalents solely from synthetic benchmark charts.

Completion

Report baseline, profile evidence, measured result, benchmark commands, correctness validation, and tradeoffs.