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pgo

README.md

Node.js PGO Training Scripts

Training workloads for Profile-Guided Optimization (PGO) builds using Clang/LLVM (including Clang-CL on Windows).

What is PGO?

PGO uses runtime profile data to guide compiler optimizations (inlining, branch prediction, code layout), typically improving throughput by 5-20%.

The process has three phases:

  1. Instrument — Build with -fprofile-generate (produces .profraw files)
  2. Train — Run representative workloads to collect profile data
  3. Optimize — Merge .profraw → node.profdata via llvm-profdata, then rebuild with -fprofile-use

Quick Start

From a VS Developer Command Prompt:

# Step 1: Build the instrumented binary
vcbuild.bat pgo-generate

# Step 2: Run workloads and merge profile data
.\pgo.ps1

# Step 3: Build the optimized binary
vcbuild.bat pgo-use

pgo.ps1 expects the instrumented binary at Release\node.exe (produced by step 1) and writes node.profdata to the repo root (consumed by step 3).

# Optionally set a longer training duration (default: 15s per script)
.\pgo.ps1 -Duration 30

Training Scripts

All scripts use only Node.js built-in modules (no npm dependencies). Each script is run as a separate process via fork(), producing its own .profraw file.

Script What it exercises
pgo-http-server.js llhttp parser, TCP stack, header serialization, JSON, routing
pgo-json.js V8 JSON parser/serializer, string allocation, GC pressure
pgo-crypto.js OpenSSL (hashing, HMAC, AES, RSA, ECDSA, random, KDF)
pgo-streams-buffers.js Buffer C++ impl, stream state machine, back-pressure
pgo-fs.js libuv fs operations, thread pool, path module
pgo-async-patterns.js V8 Promises, microtask queue, EventEmitter, timers
pgo-url-string.js Ada URL parser, V8 string internals, regex JIT
pgo-compression.js zlib, brotli C libraries, streaming compression
pgo-net.js libuv TCP/pipe handles, c-ares DNS resolver
pgo-module-loading.js Module resolver, V8 script compilation, vm module
pgo-child-workers.js Worker thread messaging, SharedArrayBuffer, inline eval

Running the Orchestrator Directly

The orchestrator can also be invoked directly (e.g. for testing individual workloads). When used with pgo.ps1, this is handled automatically.

# Run all scripts
node tools/pgo/pgo-run-all.js --duration=15 --verbose

# Run specific scripts
node tools/pgo/pgo-run-all.js --scripts=http-server,json,crypto --duration=30

# Show help
node tools/pgo/pgo-run-all.js --help

Each script reads the PGO_TRAINING_DURATION environment variable (in milliseconds) to determine how long to run. The orchestrator sets this automatically from the --duration flag (in seconds).

Files

tools/pgo/
├── pgo-run-all.js          # Training orchestrator
├── pgo-http-server.js      # HTTP server + client workload
├── pgo-json.js             # JSON parse/stringify workload
├── pgo-crypto.js           # Crypto operations workload
├── pgo-streams-buffers.js  # Streams and Buffer workload
├── pgo-fs.js               # File system operations workload
├── pgo-async-patterns.js   # Promise/async, EventEmitter, timers workload
├── pgo-url-string.js       # URL parsing, string ops, regex workload
├── pgo-compression.js      # Gzip/brotli/deflate compression workload
├── pgo-net.js              # TCP networking and DNS workload
├── pgo-module-loading.js   # Module require/import, VM compilation workload
├── pgo-child-workers.js    # Worker threads workload
└── README.md               # This file
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