mohitmishra786/low-level-dev-skills

linux-perf

Linux perf profiler skill for CPU performance analysis.

使い方

インストールコマンドをコピーし、自分の環境へ導入する前にソースを確認します。
必要なツール、認証情報、対応環境を原文で確認します。
入力と成果物を指定し、出力を資料と照合します。

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill linux-perf

開始前の確認

導入にはモデル契約、API枠、ファイルへのアクセス許可は含まれません。
スター数や導入数は活動の指標であり、独立した品質・安全性試験ではありません。

リポジトリの原文

見出し、例、コード、表、リンク、参照画像を含む原文を表示しています。

Linux perf

Purpose

Guide agents through perf for CPU profiling: sampling, hardware counter measurement, hotspot identification, and integration with flamegraph generation.

Triggers

"Which function is consuming the most CPU?"
"How do I measure cache misses / IPC?"
"How do I use perf to find hotspots?"
"How do I generate a flamegraph from perf data?"
"perf shows [unknown] or [kernel] frames"

Workflow

1. Prerequisites

bash

# Install
sudo apt install linux-perf    # Debian/Ubuntu (version-matched)
sudo dnf install perf          # Fedora/RHEL

# Check permissions
# By default perf requires root or paranoid level ≤ 1
cat /proc/sys/kernel/perf_event_paranoid
# 2 = only CPU stats (not kernel), 1 = user+kernel, 0 = all, -1 = no restrictions

# Temporarily lower (session only)
sudo sysctl -w kernel.perf_event_paranoid=1

# Persistent
echo 'kernel.perf_event_paranoid=1' | sudo tee /etc/sysctl.d/99-perf.conf
sudo sysctl -p /etc/sysctl.d/99-perf.conf

Compile the target with debug symbols for useful frame data:

bash

gcc -g -O2 -fno-omit-frame-pointer -o prog main.c
# -fno-omit-frame-pointer: essential for frame-pointer-based unwinding
# Alternative: compile with DWARF CFI and use --call-graph=dwarf

2. perf stat — quick counters

bash

# Basic hardware counters
perf stat ./prog

# With specific events
perf stat -e cache-misses,cache-references,instructions,cycles,branch-misses ./prog

# Wall-clock comparison: N runs
perf stat -r 5 ./prog

# Attach to existing process
perf stat -p 12345 sleep 10

Interpret perf stat output:

IPC (instructions per cycle) < 1.0: memory-bound or stalled pipeline
cache-miss rate > 5%: significant cache pressure
branch-miss rate > 5%: branch predictor struggling

3. perf record — sampling

bash

# Default: sample at 1000 Hz (cycles event)
perf record -g ./prog

# Specify frequency
perf record -F 999 -g ./prog

# Specific event
perf record -e cache-misses -g ./prog

# Attach to running process
perf record -F 999 -g -p 12345 sleep 30

# Off-CPU profiling (time spent waiting)
perf record -e sched:sched_switch -ag sleep 10

# DWARF call graphs (better for binaries without frame pointers)
perf record -F 999 --call-graph=dwarf ./prog

# Save to named file
perf record -o myapp.perf.data -g ./prog

4. perf report — interactive analysis

bash

perf report                          # reads perf.data
perf report -i myapp.perf.data
perf report --no-children            # self time only (not cumulative)
perf report --sort comm,dso,sym      # sort by fields
perf report --stdio                  # non-interactive text output

Navigation in TUI:

Enter — expand a symbol
a — annotate (show assembly with hit counts)
s — show source (needs debug info)
d — filter by DSO (library)
t — filter by thread
? — help

5. perf annotate — hot instructions

bash

# Show assembly with hit percentages
perf annotate sym_name

# From report: press 'a' on a symbol
# Or directly:
perf annotate -i perf.data --symbol=hot_function --stdio

High hit count on a mov or vmovdqa suggests a cache miss at that load.

6. perf top — live profiling

bash

# Live top, like 'top' but for functions
sudo perf top -g

# Filter by process
sudo perf top -p 12345

7. Feed into flamegraphs

bash

# Generate perf script output
perf script > out.perf

# Use Brendan Gregg's FlameGraph tools
git clone https://github.com/brendangregg/FlameGraph
./FlameGraph/stackcollapse-perf.pl out.perf > out.folded
./FlameGraph/flamegraph.pl out.folded > flamegraph.svg

# Open flamegraph.svg in browser

See skills/profilers/flamegraphs for reading flamegraphs and interpreting results.

8. Common issues

Problem	Cause	Fix
`Permission denied`	`perf_event_paranoid` too high	Lower paranoid level or run with `sudo`
`[unknown]` frames	Missing frame pointers or debug info	Recompile with `-fno-omit-frame-pointer` or use `--call-graph=dwarf`
`[kernel]` everywhere	Kernel symbols not visible	Use `sudo perf record`; install `linux-image-$(uname -r)-dbgsym`
`No kallsyms`	Kernel symbols unavailable	`echo 0	sudo tee /proc/sys/kernel/kptr_restrict`
Empty report for short program	Program exits too fast	Use `-F 9999` or instrument longer workload
DWARF unwinding slow	Large DWARF stack	Limit with `--call-graph dwarf,512`

9. Useful events

bash

# List all available events
perf list

# Common hardware events
cycles
instructions
cache-references
cache-misses
branch-instructions
branch-misses
stalled-cycles-frontend
stalled-cycles-backend

# Software events
context-switches
cpu-migrations
page-faults

# Tracepoints (requires root)
sched:sched_switch
syscalls:sys_enter_read

For a counter reference and interpretation guide, see references/events.md.

Related skills

Use skills/profilers/flamegraphs for SVG flamegraph generation and reading
Use skills/profilers/valgrind for cache simulation and memory profiling
Use skills/compilers/gcc or skills/compilers/clang for PGO from perf data (AutoFDO)

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導入数: 2
GitHub Stars: 267
更新日: 6月27日

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flamegraphs

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.

導入数: 2
GitHub Stars: 267
更新日: 6月27日

MIT2 ファイル

詳細を見る →

linux-perf

使い方

開始前の確認

Linux perf

Purpose

Triggers

Workflow

1. Prerequisites

2. perf stat — quick counters

3. perf record — sampling

4. perf report — interactive analysis

5. perf annotate — hot instructions

6. perf top — live profiling

7. Feed into flamegraphs

8. Common issues

9. Useful events

Related skills

タスクに関連する項目

code-review

diagnosing-bugs

rea-ci-tests-audit

diagnosing-superpowers

関連する Skills

core-dumps

custom-allocators

ebpf

flamegraphs