| name | rust-profiling |
| description | Profile Rust code using samply and related evidence to identify CPU bottlenecks, allocation hot paths, and allocator-fragmentation symptoms. Use when performance is slow, RSS grows unexpectedly, before optimizing, or when the user asks to profile. |
Rust Profiling with Samply
Profile Rust binaries to find CPU bottlenecks and allocation pressure using samply, then use OS-level memory evidence when RSS or fragmentation is the symptom.
Quick Start
cargo build --profile profiling
samply record ./target/profiling/<binary> [args...]
samply record --save-only -o profile.json ./target/profiling/<binary>
python3 ~/.agents/skills/rust-profiling/scripts/analyze_profile.py profile.json
Skill Files
| File | Purpose |
|---|
reference.md | Cargo.toml setup, samply options, troubleshooting |
examples.md | Common profiling scenarios and analysis patterns |
optimization.md | Post-profiling fixes: source patterns, release-profile tuning, PGO, BOLT, what doesn't work |
scripts/analyze_profile.py | CLI tool to analyze saved profile.json files |
When to Use
- Performance is slower than expected
- RSS or heap usage grows unexpectedly under load
- Before optimizing (measure first!)
- After optimization (verify improvement)
- Investigating CPU-bound operations or allocation-heavy hot paths
When NOT to Use
- The task is a Rust correctness bug, API design question, or refactor without a performance symptom.
- The user already has a narrow benchmark request that does not need profiling guidance.
- The issue is build time, binary size, or dependency hygiene rather than runtime CPU, memory, or contention.
What to Look For
| Pattern | Meaning | Action |
|---|
| High self-time | Function itself is slow | Direct optimization target |
| High total-time | Called often or slow callees | Check call frequency |
malloc/alloc in hot path | Allocation overhead | Preallocate, reuse, pool, or use bounded/shared buffers |
| RSS grows then plateaus while profiles show allocation churn | Possible allocator fragmentation, not necessarily a leak | Compare allocators, then reduce high-rate small allocations |
pthread_mutex/parking_lot | Lock contention | Reduce lock scope or use lock-free |
