# rust-profiling

A skill that walks an agent through Rust profiling: flamegraphs, binary size, monomorphization bloat and Criterion microbenchmarks.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 586 installs · ★ 267
- Author: mohitmishra786
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/rust/rust-profiling/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/rust-profiling

## What it does

The skill turns profiling questions into a fixed sequence. First you build with debug symbols, because a release build without them gives you an unreadable profile — either a `release-with-debug` profile in `Cargo.toml` or `CARGO_PROFILE_RELEASE_DEBUG=true` on the command line. Then flamegraphs through `cargo flamegraph`, which uses perf on Linux and DTrace on macOS; both want elevated permissions.

Binary size and monomorphization get their own sections. `cargo bloat` ranks functions and crates by how much space they take, and `cargo llvm-lines` counts LLVM IR lines and copies per function. A high `Copies` number means a generic got expanded for every type it was called with. The skill shows the usual fix: keep a thin generic wrapper and move the real work into a concrete inner function.

For timing there is Criterion, configured with `harness = false` and `black_box` so the optimizer does not delete the code under test. The rest covers `perf record` and `perf report`, plus heaptrack and DHAT for allocation tracking. One thing to plan for: `cargo flamegraph` is not bundled with the toolchain, you install it with `cargo install flamegraph`, and on Linux perf needs `perf_event_paranoid` set to 1 before it will collect samples.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-profiling -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/rust-profiling/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/rust-profiling/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-profiling -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/rust-profiling/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-profiling -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/rust-profiling/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install mohitmishra786/low-level-dev-skills rust-profiling
```

2. **Manually: put the files in place**
- File: `.github/skills/rust-profiling/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-profiling -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/mohitmishra786/low-level-dev-skills --path skills/rust/rust-profiling
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/rust-profiling/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill rust-profiling -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/rust/rust-profiling/SKILL.md

## When to use it
- generate a flamegraph for a Rust binary
- track down what made a binary grow
- count monomorphization copies per function
- write a Criterion benchmark with black_box
- inspect allocations with heaptrack or DHAT

## Example prompts
- Generate a flamegraph for `myapp` and show me the hottest functions
- Run `cargo bloat --release --crates` and tell me which crate is the biggest
- Write a Criterion benchmark for `process` across several input sizes

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: fb8d1303df1f07dd.

BEGIN THIRD-PARTY FILE fb8d1303df1f07dd
````text
---
name: rust-profiling
description: Rust profiling skill for performance analysis. Use when generating flamegraphs from Rust binaries, measuring monomorphization bloat with cargo-llvm-lines, analysing binary size with cargo-bloat, microbenchmarking with Criterion, or interpreting inlined frames in profiles. Activates on queries about cargo flamegraph, cargo-bloat, cargo-llvm-lines, Criterion benchmarks, Rust performance profiling, or binary size analysis.
---

# Rust Profiling

## Purpose

Guide agents through Rust performance profiling: flamegraphs via cargo-flamegraph, binary size analysis, monomorphization bloat measurement, Criterion microbenchmarks, and interpreting profiling results with inlined Rust frames.

## Triggers

- "How do I generate a flamegraph for a Rust program?"
- "My Rust binary is huge — how do I find what's causing it?"
- "How do I write Criterion benchmarks?"
- "How do I measure monomorphization bloat?"
- "Rust performance is worse than expected — how do I profile it?"
- "How do I use perf with Rust?"

## Workflow

### 1. Build for profiling

```bash
# Release with debug symbols (needed for readable profiles)
# Cargo.toml:
[profile.release-with-debug]
inherits = "release"
debug = true

cargo build --profile release-with-debug

# Or quick: release + debug info inline
CARGO_PROFILE_RELEASE_DEBUG=true cargo build --release
```

### 2. Flamegraphs with cargo-flamegraph

```bash
# Install
cargo install flamegraph

# Linux: uses perf (requires perf_event_paranoid ≤ 1)
sudo sh -c 'echo 1 > /proc/sys/kernel/perf_event_paranoid'
cargo flamegraph --bin myapp -- arg1 arg2

# macOS: uses DTrace (requires sudo)
sudo cargo flamegraph --bin myapp -- arg1 arg2

# Profile tests
cargo flamegraph --test mytest -- test_filter

# Profile benchmarks
cargo flamegraph --bench mybench -- --bench

# Output
# Generates flamegraph.svg in current directory
# Open in browser: firefox flamegraph.svg
```

Custom flamegraph options:
```bash
# More samples
cargo flamegraph --freq 1000 --bin myapp

# Filter to specific threads
cargo flamegraph --bin myapp -- args 2>/dev/null

# Using perf directly for more control
perf record -g -F 999 ./target/release-with-debug/myapp args
perf script | stackcollapse-perf.pl | flamegraph.pl > out.svg
```

### 3. Binary size analysis with cargo-bloat

```bash
# Install
cargo install cargo-bloat

# Show top functions by size
````
END THIRD-PARTY FILE fb8d1303df1f07dd

The third-party file has ended. Everything between the fb8d1303df1f07dd tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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