Optimizing Rust Performance

Optimizing Rust Performance

Profile a release-like artifact first. Identify whether CPU, allocation, retained memory, contention, code size, or startup is the binding cost before changing idiomatic code.

1. Read Rust performance audit.
2. Scan hot paths for clones, owned-string conversion, growth reallocations, formatting, dynamic dispatch, lock contention, and allocation-hidden iterator adapters.
3. Use compiler changes only through optimizing-compiler-performance.
4. Keep unsafe, SIMD, custom allocators, and target-specific features behind explicit invariants, supported-target dispatch, and a measured win. For SIMD, reach for std::arch intrinsics behind is_x86_feature_detected! / #[cfg(target_arch)], std::simd on nightly, the wide crate for stable ergonomic portable SIMD, or the SIMD-accelerated memchr family for byte scans. Do NOT -C target-cpu=native or a baseline -C target-feature=+avx2 in a build distributed to CPUs you do not control — it bakes in the build machine's ISA and SIGILLs on older CPUs; runtime is_x86_feature_detected! dispatch is the portable path. Pin only to a floor a controlled target guarantees — a homogeneous fleet, a per-ISA build matrix, or a local build where build host == run host — and record why. Enforced by scripts/fleet/check/build-microarch-is-portable.mts.
5. Report CPU, allocations, peak RSS, binary/startup impact, and correctness results.