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
# 1. Ensure profiling profile exists in Cargo.toml (see reference.md)
# 2. Build with debug symbols
cargo build --profile profiling
# 3. Profile (opens Firefox Profiler UI)
samply record ./target/profiling/<binary> [args...]
# 4. Or save for CLI analysis
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 |
