Flamegraphs

mohitmishra786/low-level-dev-skills/skills/profilers/flamegraphs

by mohitmishra786bdc58472fa9fNo license253 starsListed Oct 9, 2026Updated Oct 9, 2026Repository updated 3 months ago

Flamegraph generation and interpretation skill. Use when converting perf, Valgrind Callgrind, or other profiler output into SVG flamegraphs using Brendan Gregg's FlameGraph tools, or when reading flamegraphs to identify performance bottlenecks. Activates on queries about flamegraphs, stackcollapse, flamegraph.svg, identifying hot frames, wide vs tall frames, or performance visualisation.

Instructions onlySoftware DevelopmentData & Analytics
AI-generated overview

Guides generating SVG flamegraphs from profiler output and interpreting them to find performance bottlenecks.

What it does
This skill walks an agent through the pipeline from profiler data to an SVG flamegraph using Brendan Gregg's FlameGraph tools, covering perf, Valgrind Callgrind, Go pprof, DTrace and async-profiler inputs. It also explains how to read flamegraphs, including wide versus tall frames, differential before/after charts, and flamegraph.pl options. It produces command sequences and interpretation guidance rather than files itself.
When to use it
Use it when converting perf, Callgrind or other profiler output into SVG flamegraphs, or when reading an existing flamegraph to locate hot frames. It also fits comparing before/after profiles with a differential flamegraph.
Requirements
Requires the FlameGraph tool scripts (stackcollapse-perf.pl, flamegraph.pl, difffolded.pl and related), plus the relevant profiler such as perf, Valgrind Callgrind, Go pprof, DTrace or async-profiler. It ships no scripts of its own and needs no credentials, though cloning the FlameGraph repository requires network access.

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 repoexport PATH=$PATH:/path/to/FlameGraph

2. perf → flamegraph (most common path)

bash
# Step 1: recordperf record -F 999 -g -o perf.data ./prog
# Step 2: generate script outputperf script -i perf.data > out.perf
# Step 3: collapse stacksstackcollapse-perf.pl out.perf > out.folded
# Step 4: generate SVGflamegraph.pl out.folded > flamegraph.svg
# Step 5: viewxdg-open flamegraph.svg     # Linuxopen flamegraph.svg          # macOS

One-liner:

bash
perf record -F 999 -g ./prog && perf script | stackcollapse-perf.pl | flamegraph.pl > fg.svg

3. Differential flamegraph (before/after)

bash
# Collect two profilesperf record -g -o before.data ./prog_oldperf record -g -o after.data ./prog_new
# Collapseperf script -i before.data | stackcollapse-perf.pl > before.foldedperf script -i after.data  | stackcollapse-perf.pl > after.folded
# Diff (red = regressed, blue = improved)difffolded.pl before.folded after.folded | flamegraph.pl > diff.svg

4. Callgrind → flamegraph

bash
valgrind --tool=callgrind --callgrind-out-file=cg.out ./progstackcollapse-callgrind.pl cg.out | flamegraph.pl > fg.svg

5. Other profiler inputs

bash
# Go pprofgo tool pprof -raw -output=prof.txt progstackcollapse-go.pl prof.txt | flamegraph.pl > fg.svg
# DTracedtrace -x ustackframes=100 -n 'profile-99 /execname=="prog"/ { @[ustack()] = count(); }' \  -o out.stacks sleep 10stackcollapse.pl out.stacks | flamegraph.pl > fg.svg
# Java (async-profiler)async-profiler -d 30 -f out.collapsed PIDflamegraph.pl out.collapsed > fg.svg

6. 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:

PatternMeaningAction
Wide frame near bottomFunction itself is hotOptimise that function
Wide frame with tall narrow towersCalling many different calleesHot dispatch; reduce call overhead
Very tall stack with wide baseDeep recursionCheck recursion depth; consider iterative approach
Plateau at the topLeaf function with no calleesThis leaf is the actual hotspot
Many narrow identical stacksMany threads doing the same workConsider parallelism or batching

Identifying the actionable hotspot:

  1. Find the widest top frame (a frame with no or narrow children above it)
  2. That is where CPU time is actually spent
  3. 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
OptionEffect
--titleSVG title
--widthWidth in pixels
--heightFrame height in pixels
--minwidthOmit frames < N% (reduces clutter)
--colorsPalette: hot (default), mem, io, java, js, perl, red, green, blue
--invertedIcicle chart (roots at top)
--reverseReverse stacks
--cpConsistent palette (same frame = same color across SVGs)

References

For tool installation, stackcollapse scripts, and palette options, see references/tools.md [blocked].

Related skills

  • Use skills/profilers/linux-perf to collect perf data
  • Use skills/profilers/valgrind to collect Callgrind data
  • Use skills/compilers/clang for LLVM PGO from sampling profiles

Source and attribution

Source:mohitmishra786/low-level-dev-skillsinskills/profilers/flamegraphsat commitbdc5847

License: No license

Content belongs to its original authors. SourceWeft indexes it from a public repository.

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Flamegraphs · skills/profilers/flamegraphs Agent Skill | SourceWeft