# hardware-counters

Guides agents through hardware performance counter profiling with perf and PAPI. It computes IPC, measures cache miss rates, and maps PMU events to source code.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 545 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/profilers/hardware-counters/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/hardware-counters

## What it does

The skill equips coding agents with workflows for CPU hardware performance counters. It covers baseline `perf stat` runs to derive instructions per cycle (IPC), cycles per instruction, and misses per kilo-instructions (MPKI). When generic counter aliases are insufficient, it provides steps to query raw PMU event codes using `ocperf` or `libpfm4`.

For hotspot investigation, it guides users through `perf record` and `perf annotate`. This setup pinpoints exact lines causing cache misses or branch mispredictions. Debug symbols are mandatory here: without `-g` during compilation, the tool cannot map assembly addresses back to source code.

It also includes C implementation examples using the PAPI library for in-process counter reads. Separate instructions cover building Intel PCM via CMake to inspect memory bandwidth and per-socket metrics.

## Install

### Claude Code (native platform)

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

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

### Codex

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

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

### Cursor

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

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

### GitHub Copilot

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

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

### Gemini CLI

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

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

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill hardware-counters -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/profilers/hardware-counters/SKILL.md

## When to use it
- compute IPC and evaluate memory bottlenecks using MPKI
- isolate source lines responsible for LLC cache misses
- measure branch misprediction rates with perf stat
- instrument C programs using the PAPI hardware counter library
- track memory bandwidth over time via Intel PCM

## Example prompts
- How do I measure L1 and LLC cache miss rates for ./prog using perf stat?
- Show me how to correlate LLC-load-misses to source lines with perf annotate.
- Write a C code snippet using PAPI to count instructions, cycles, and branch mispredictions.

## 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: bd8777337e1bf970.

BEGIN THIRD-PARTY FILE bd8777337e1bf970
````text
---
name: hardware-counters
description: Hardware performance counter skill for low-level CPU analysis. Use when collecting PMU events with perf stat, using the PAPI library, measuring cache miss rates and branch misprediction ratios, computing IPC, or correlating PMU events to source lines. Activates on queries about hardware counters, PMU events, perf stat -e, PAPI, cache miss rate, branch misprediction, IPC measurement, or CPU performance events.
---

# Hardware Performance Counters

## Purpose

Guide agents through hardware performance counter analysis: collecting PMU events with `perf stat -e`, using the PAPI library for portable counter access, interpreting cache miss rates and branch misprediction ratios, computing IPC, and correlating events to source lines with `perf annotate`.

## Triggers

- "How do I measure cache miss rate with perf?"
- "How do I count branch mispredictions?"
- "How do I compute IPC (instructions per clock) with perf?"
- "How do I use the PAPI library for hardware counters?"
- "How do I see which source lines cause the most cache misses?"
- "How do I measure memory bandwidth with performance counters?"

## Workflow

### 1. perf stat — basic counter collection

```bash
# Basic hardware event summary
perf stat ./prog

# Output:
#  Performance counter stats for './prog':
#
#      1,234,567,890      instructions
#        456,789,012      cycles
#         12,345,678      cache-misses         #    1.23 % of all cache refs
#         23,456,789      branch-misses        #    2.34 % of all branches
#
#       0.456789012 seconds time elapsed

# Derived metrics (computed from the output)
# IPC = instructions / cycles = 1,234,567,890 / 456,789,012 ≈ 2.70
# CPI = cycles / instructions ≈ 0.37
```

### 2. Specifying PMU events with -e

```bash
# Specific hardware events
perf stat -e instructions,cycles,cache-misses,branch-misses ./prog

# L1/L2/L3 cache events
perf stat -e \
  L1-dcache-loads,L1-dcache-load-misses,\
  L2-loads,L2-load-misses,\
  LLC-loads,LLC-load-misses \
  ./prog

# Memory bandwidth (Intel)
perf stat -e \
  uncore_imc/cas_count_read/,\
  uncore_imc/cas_count_write/ \
  ./prog

# TLB misses
perf stat -e dTLB-loads,dTLB-load-misses,iTLB-loads,iTLB-load-misses ./prog

# Branch misprediction rate
perf stat -e branches,branch-misses ./prog
# Rate = branch-misses / branches × 100%

# Available events (varies by CPU)
perf list hardware          # generic hardware events
perf list cache             # cache events
perf list pmu               # raw PMU events for your CPU
```

### 3. Key metrics and thresholds
````
END THIRD-PARTY FILE bd8777337e1bf970

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