Tous les Skills / MOHITMISHRA786

mohitmishra786/low-level-dev-skills

rust-profiling

Rust profiling skill for performance analysis.

Mode d’emploi

Copiez la commande et examinez le paquet avant de l’installer dans votre environnement agent.
Consultez le document original pour les outils, identifiants et environnements requis.
Décrivez les entrées et le livrable souhaité ; comparez la sortie aux sources.

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill rust-profiling

Avant de commencer

L’installation n’inclut ni abonnement au modèle, ni quota API, ni accès aux fichiers.
Étoiles et installations reflètent l’activité, pas un test indépendant de qualité ou de sécurité.

Document Skill original

Rendu depuis le dépôt source en conservant titres, exemples, code, tableaux, liens et images.

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
cargo bloat --release -n 20

# Show per-crate size breakdown
cargo bloat --release --crates

# Include only specific crate
cargo bloat --release --filter myapp

# Compare before/after a change
cargo bloat --release --crates > before.txt
# make changes
cargo bloat --release --crates > after.txt
diff before.txt after.txt

Typical output:

 File  .text    Size    Crate Name
 2.4%   3.0% 47.0KiB      std <std macros>
 1.8%   2.3% 35.5KiB   myapp myapp::heavy_module::process
 1.2%   1.5% 23.1KiB    serde serde::de::...

4. Monomorphization bloat with cargo-llvm-lines

bash

# Install
cargo install cargo-llvm-lines

# Show LLVM IR line counts (proxy for monomorphization)
cargo llvm-lines --release | head -40

# Filter to your crate only
cargo llvm-lines --release | grep '^myapp'

Typical output:

   Lines      Copies  Function name
   85330           1  [LLVM passes]
    7761          92  core::fmt::write
    4672          11  myapp::process::<impl MyTrait for T>
    3201          47  <alloc::vec::Vec<T> as core::ops::Drop>::drop

High Copies count = monomorphization expansion. Fix:

rust

// Before: generic, gets monomorphized for every T
fn process<T: AsRef<[u8]>>(data: T) -> usize {
    do_work(data.as_ref())
}

// After: thin generic wrapper + concrete inner
fn process<T: AsRef<[u8]>>(data: T) -> usize {
    fn inner(data: &[u8]) -> usize { do_work(data) }
    inner(data.as_ref())
}

5. Criterion microbenchmarks

toml

# Cargo.toml
[dev-dependencies]
criterion = { version = "0.5", features = ["html_reports"] }

[[bench]]
name = "my_bench"
harness = false

rust

// benches/my_bench.rs
use criterion::{black_box, criterion_group, criterion_main, Criterion, BenchmarkId};

fn bench_process(c: &mut Criterion) {
    // Simple benchmark
    c.bench_function("process 1000 items", |b| {
        let data: Vec<i32> = (0..1000).collect();
        b.iter(|| process(black_box(&data)))  // black_box prevents optimization
    });
}

fn bench_sizes(c: &mut Criterion) {
    let mut group = c.benchmark_group("process_sizes");

    for size in [100, 1000, 10000].iter() {
        let data: Vec<i32> = (0..*size).collect();
        group.bench_with_input(
            BenchmarkId::from_parameter(size),
            &data,
            |b, data| b.iter(|| process(black_box(data))),
        );
    }
    group.finish();
}

criterion_group!(benches, bench_process, bench_sizes);
criterion_main!(benches);

bash

# Run all benchmarks
cargo bench

# Run specific benchmark
cargo bench --bench my_bench

# Run with filter
cargo bench -- process_sizes

# Compare with baseline (save/load)
cargo bench -- --save-baseline before
# make changes
cargo bench -- --baseline before

# View HTML report
open target/criterion/report/index.html

6. perf with Rust (Linux)

bash

# Record
perf record -g ./target/release-with-debug/myapp args
perf record -g -F 999 ./target/release-with-debug/myapp args  # higher freq

# Report
perf report                     # interactive TUI
perf report --stdio --no-call-graph | head -40   # text

# Annotate specific function
perf annotate myapp::hot_function

# stat (quick counters)
perf stat ./target/release/myapp args

Rust-specific perf tips:

Build with debug = 1 (line tables only) for faster builds with line-level attribution
Use RUSTFLAGS="-C force-frame-pointers=yes" for better call graphs without DWARF unwinding
Disable ASLR for reproducible addresses: setarch $(uname -m) -R ./myapp

7. heaptrack / DHAT for allocations

bash

# heaptrack (Linux)
heaptrack ./target/release/myapp args
heaptrack_print heaptrack.myapp.*.zst | head -50

# DHAT via Valgrind
valgrind --tool=dhat ./target/debug/myapp args
# Open dhat-out.* with dh_view.html

For flamegraph setup and Criterion configuration, see references/cargo-flamegraph-setup.md.

Related skills

Use skills/rust/rustc-basics for build configuration (debug symbols, profiles)
Use skills/profilers/linux-perf for perf fundamentals
Use skills/profilers/flamegraphs for reading and interpreting flamegraph SVGs
Use skills/profilers/valgrind for allocation profiling with massif/DHAT

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