Cómo usar
- Copia el comando y revisa el paquete antes de instalarlo en tu entorno de agente.
- Consulta las herramientas, credenciales y entornos necesarios en el documento original.
- Describe las entradas y el resultado deseado; contrasta la salida con las fuentes.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill flamegraphsAntes de empezar
- La instalación no incluye suscripción al modelo, cuota API ni permisos sobre tus archivos.
- Las estrellas e instalaciones reflejan actividad, no una prueba independiente de calidad o seguridad.
Documento original del Skill
Contenido del repositorio de origen con títulos, ejemplos, código, tablas, enlaces e imágenes preservados.
Flamegraphs
Purpose
Guide agents through the pipeline from profiler data to SVG flamegraph, and teach interpretation of flamegraphs to drive concrete optimisation decisions.
Triggers
- "How do I generate a flamegraph from perf data?"
- "How do I read a flamegraph?"
- "The flamegraph shows a wide frame — what does that mean?"
- "How do I generate a flamegraph from Callgrind?"
- "I want to compare two flamegraphs (before/after)"
Workflow
1. Install FlameGraph tools
bash
git clone https://github.com/brendangregg/FlameGraph
# No install needed; scripts are in the repo
export PATH=$PATH:/path/to/FlameGraph2. perf → flamegraph (most common path)
bash
# Step 1: record
perf record -F 999 -g -o perf.data ./prog
# Step 2: generate script output
perf script -i perf.data > out.perf
# Step 3: collapse stacks
stackcollapse-perf.pl out.perf > out.folded
# Step 4: generate SVG
flamegraph.pl out.folded > flamegraph.svg
# Step 5: view
xdg-open flamegraph.svg # Linux
open flamegraph.svg # macOSOne-liner:
bash
perf record -F 999 -g ./prog && perf script | stackcollapse-perf.pl | flamegraph.pl > fg.svg3. Differential flamegraph (before/after)
bash
# Collect two profiles
perf record -g -o before.data ./prog_old
perf record -g -o after.data ./prog_new
# Collapse
perf script -i before.data | stackcollapse-perf.pl > before.folded
perf script -i after.data | stackcollapse-perf.pl > after.folded
# Diff (red = regressed, blue = improved)
difffolded.pl before.folded after.folded | flamegraph.pl > diff.svg4. Callgrind → flamegraph
bash
valgrind --tool=callgrind --callgrind-out-file=cg.out ./prog
stackcollapse-callgrind.pl cg.out | flamegraph.pl > fg.svg5. Other profiler inputs
bash
# Go pprof
go tool pprof -raw -output=prof.txt prog
stackcollapse-go.pl prof.txt | flamegraph.pl > fg.svg
# DTrace
dtrace -x ustackframes=100 -n 'profile-99 /execname=="prog"/ { @[ustack()] = count(); }' \
-o out.stacks sleep 10
stackcollapse.pl out.stacks | flamegraph.pl > fg.svg
# Java (async-profiler)
async-profiler -d 30 -f out.collapsed PID
flamegraph.pl out.collapsed > fg.svg6. Reading flamegraphs
A flamegraph is a call-stack visualisation:
- X axis: time on CPU (not time sequence) — wider = more time
- Y axis: call stack depth — taller = deeper call chain
- Color: random (no significance) — unless using differential mode
What to look for:
| Pattern | Meaning | Action |
|---|---|---|
| Wide frame near bottom | Function itself is hot | Optimise that function |
| Wide frame with tall narrow towers | Calling many different callees | Hot dispatch; reduce call overhead |
| Very tall stack with wide base | Deep recursion | Check recursion depth; consider iterative approach |
| Plateau at the top | Leaf function with no callees | This leaf is the actual hotspot |
| Many narrow identical stacks | Many threads doing the same work | Consider parallelism or batching |
Identifying the actionable hotspot:
- Find the widest top frame (a frame with no or narrow children above it)
- That is where CPU time is actually spent
- Trace down to understand what called it and why
Differential flamegraph:
- Red frames: more time in new profile (regression)
- Blue frames: less time in new profile (improvement)
- Frames only in one profile appear solid colored
7. flamegraph.pl options
bash
flamegraph.pl --title "My App" \
--subtitle "Release build, workload X" \
--width 1600 \
--height 16 \
--minwidth 0.5 \
--colors java \
out.folded > fg.svg| Option | Effect |
|---|---|
--title | SVG title |
--width | Width in pixels |
--height | Frame height in pixels |
--minwidth | Omit frames < N% (reduces clutter) |
--colors | Palette: hot (default), mem, io, java, js, perl, red, green, blue |
--inverted | Icicle chart (roots at top) |
--reverse | Reverse stacks |
--cp | Consistent palette (same frame = same color across SVGs) |
References
For tool installation, stackcollapse scripts, and palette options, see references/tools.md.
Related skills
- Use
skills/profilers/linux-perfto collect perf data - Use
skills/profilers/valgrindto collect Callgrind data - Use
skills/compilers/clangfor LLVM PGO from sampling profiles
