Steam Affinity

A lightweight Windows utility that automatically sets CPU affinity for games and processes launched by Steam. It automatically identifies and excludes the first physical core (Logical Processors 0 & 1 on HT/SMT systems). This generally improves raw CPU performance by around 2-5% by avoiding the core heavily used by the OS kernel, interrupts, and background tasks.

Features

• Automatic Detection: Monitors processes launched by steam.exe.
• Hardware-Aware Affinity: Automatically detects your CPU topology (Hyper-Threading/SMT) and disables only the first physical core (which handles OS interrupts and background tasks).
  • On HT/SMT systems: Disables Logical Processors 0 and 1.
  • On non-HT/SMT systems: Disables only Logical Processor 0.
• System Tray Integration: Runs silently in the background with a system tray icon.
• Log Viewer: Built-in log window to see which processes are being modified.
• Startup Management: Option to automatically start when you log in.

Installation

Installer (Recommended)

Download and run the .msi installer from the releases page (or build it yourself). This will:

• Install the application to Program Files.
• Create a Start Menu shortcut.

Manual

You can also run the standalone executable:

cargo run --release

Building from Source

Prerequisites

• Rust
• WiX Toolset v3 (for building the installer)

Build Steps

1. Build the executable

   cargo build --release

2. Build the MSI installer

   # Ensure WiX v3 bin folder is in your PATH
   cargo wix

   or

   cargo wix --bin-path "C:\Program Files (x86)\WiX Toolset v3.14\bin" --nocapture

   The installer will be generated in target/wix/steam_affinity-x.y.z-x86_64.msi.

Usage

Once running, Steam Affinity sits in your system tray (gear icon).

Tray Menu Options:

• Show Logs: Opens a window displaying recent actions and detected processes.
• Monitoring: Toggle the automatic affinity adjustment on/off.
• Start on Login: Toggle whether the app starts automatically with Windows.
• Exit: Closes the application.

Configuration

The application supports command-line arguments for advanced usage:

steam_affinity.exe --verbose --interval-ms 3000

• --verbose: Enable detailed logging to stdout (useful for debugging).
• --interval-ms <MS>: Set the polling interval in milliseconds (default: 3000ms).

Technical Details

• Uses CreateToolhelp32Snapshot to snapshot running processes.
• Identifies steam.exe and monitors for new child processes.
• Uses GetLogicalProcessorInformation to determine the mask for Physical Core 0.
• Applies SetProcessAffinityMask to identified children, ensuring the first physical core is excluded while all other cores remain active.
• Stores startup configuration in HKCU\Software\Microsoft\Windows\CurrentVersion\Run.