CPU Affinity Tool

Windows utility for managing CPU affinity of games and background applications.

• Primary stable released platform: Windows
• Linux desktop beta: source build on x86_64 glibc, manual smoke on X11 or Wayland, plus prerelease artifacts under linux-beta-v* tags
• Stable download artifact: Windows only
• Linux beta prereleases: GitHub Releases
• Download: Latest Release
• License: MIT

What problem it solves

Games, browsers, launchers, Discord, overlays, recording tools, and work apps can compete for the same CPU time. Windows can handle many workloads well on its own, but some systems behave better when the foreground workload and background workload are kept apart.

CPU Affinity Tool lets you save and apply repeatable launch rules instead of reopening Task Manager or re-running command-line commands every time.

It is meant to give you explicit control over:

• which CPU cores an app can use
• which priority class an app starts with
• whether those settings should be re-applied while the app is running

This is a control tool, not a promise of better FPS.

Who this is for

• Gamers who keep browsers, Discord, launchers, overlays, or recording tools open in the background
• Users with hybrid CPUs, multi-chiplet CPUs, or other workloads where core placement matters
• Users who want repeatable launch rules instead of one-off Task Manager changes
• Users who want saved affinity and priority rules for a fixed set of games or applications

Features

• Save CPU core groups for different workloads
• Launch apps with saved affinity and priority rules
• Add apps from direct paths and launcher files with Open App
• Add supported installed apps with Find Installed (Start-backed entries on Windows, desktop entries plus matching PATH executables during search on Linux beta)
• Re-apply affinity and priority while Auto Re-apply Affinity and Priority is enabled
• Autorun selected apps with the tool
• Add targets by drag and drop
• Inspect launch and automatic CPU affinity re-apply activity in the built-in log view
• Open the active data folder directly from the log screen
• Switch between light, dark, and system theme modes

When it helps

• A game is CPU-bound and background apps are competing for the same cores
• You have heavy background activity such as browsers, voice chat, launchers, or recording tools
• Your CPU layout is asymmetric or segmented, such as hybrid-core or multi-chiplet designs
• You want a repeatable launch layout that stays consistent across runs

When it does not

• The real bottleneck is the GPU
• Your background load is already light enough that contention is negligible
• The game or application does not respond well to affinity pinning
• Windows scheduling already behaves well for your workload

For a longer explanation, see docs/why.md.

Quick Start

1. Download the latest Windows release and run cpu-affinity-tool.exe.
2. Accept the UAC prompt. The current Windows build requires administrator rights.
3. Create a CPU core group for the workload you want to isolate.
4. Add an app with Open App, Find Installed, or drag and drop.
5. Set the desired affinity and priority, then save the rule.
6. Launch the app from the tool and keep Auto Re-apply Affinity and Priority enabled if you want settings re-applied automatically.

Comparison

Tool	Saved launch rules	Auto Re-apply Affinity and Priority	Complexity	Best fit
CPU Affinity Tool	Yes	Yes	Low	Focused Windows affinity workflows with saved rules
Task Manager	No	No	Low	One-off manual changes
Process Lasso	Yes	Yes	Medium	Broader third-party process automation on Windows
PowerShell / CLI methods	Script-dependent	Script-dependent	High	Users who want fully manual or scripted control

See docs/comparison.md for a fuller breakdown.

FAQ

Does it improve FPS?

Not by itself. It can help when CPU contention is real, but it is not a guaranteed FPS booster.

Does it work for every game?

No. Some games benefit, some show little change, and some do not react well to manual affinity pinning.

Do I need administrator privileges?

Yes. The current Windows release is built with requireAdministrator, so you should expect a UAC prompt on launch.

Can Windows or the application override affinity settings?

Yes. Some applications or helper processes may change affinity or priority after launch. That is why the tool includes automatic CPU affinity re-apply behavior for app processes.

Is this an alternative to Process Lasso?

It overlaps with a narrower part of that use case. CPU Affinity Tool is a focused Windows utility for saved affinity and priority workflows, not a full replacement for every Process Lasso feature.

Is Linux or macOS supported?

Windows is the only stable published release artifact today. Linux has a desktop beta path from source for x86_64 glibc systems; normal desktop sessions on X11 or Wayland are covered by manual beta smoke validation, and Linux beta prereleases are published separately under linux-beta-v* tags. There is still no stable Linux release, installer, AppImage, or Flatpak. macOS is not supported.

Where is the configuration stored?

If state.json already exists next to the executable, the app keeps using that legacy sidecar file. Otherwise, new Windows installs default to %LOCALAPPDATA%\CpuAffinityTool\state.json.

Troubleshooting

The app I want is not listed in Find Installed

Use Open App instead. On Windows, Find Installed is a launch-safe subset of Start-backed apps. On Linux beta, it primarily uses desktop entries and only surfaces matching PATH executables when you search, so it may still miss portable apps or targets outside normal launcher and shell paths.

Affinity or priority is not applied

• Make sure you launched the target from CPU Affinity Tool
• Keep Auto Re-apply Affinity and Priority enabled if the app changes settings after launch
• Verify that you accepted the UAC prompt and the tool is running elevated

The application overrides the configured settings

Some applications spawn helper processes or reset their own settings. Auto Re-apply Affinity and Priority is designed to correct that, but it may not cover every application behavior.

Windows security software or antivirus prompts appear

The current release is a Windows executable that requests elevation. Verify that you downloaded it from the official release page and that the prompt matches the expected executable path.

Shortcut or launch path behavior looks wrong

Try Open App with the direct executable or launcher path. For installed apps, try Find Installed first and fall back to Open App if the target is not listed correctly.

Build from source

Supported build targets:

• Windows release path
• Linux desktop beta path from source
• Rust stable toolchain

Windows release build:

cargo build --release --features windows --bin cpu-affinity-tool

Linux beta run/build:

cargo run --features linux --bin cpu-affinity-tool-linux
cargo build --release --features linux --bin cpu-affinity-tool-linux

Linux beta notes:

• supported target: x86_64 Linux with glibc
• expected environment for manual beta smoke: desktop session on X11 or Wayland
• Linux CI and prerelease builds run on pinned ubuntu-24.04 GitHub-hosted runners
• Debian/Ubuntu-like systems may need libclang-dev libgtk-3-dev libxcb-render0-dev libxcb-shape0-dev libxcb-xfixes0-dev libxkbcommon-dev libssl-dev before building
• Linux beta prereleases are published separately under linux-beta-v* tags as a raw binary, tar.gz, and SHA256SUMS.txt
• Linux still does not have a stable published release artifact
• tray/taskbar/focus behavior still does not have Windows parity

Useful verification commands:

cargo fmt --all -- --check
cargo clippy --features windows --bin cpu-affinity-tool -- -D warnings
cargo test --manifest-path libs/os_api/Cargo.toml
cargo test --features windows --bin cpu-affinity-tool
cargo build --release --features windows --bin cpu-affinity-tool
cargo test --features linux --bin cpu-affinity-tool-linux
cargo build --release --features linux --bin cpu-affinity-tool-linux

Expected Windows artifact:

target/release/cpu-affinity-tool.exe

For release-process details, see docs/release-process.md.

Contributing, Support, Security, License

• Contributing guide: CONTRIBUTING.md
• Support and diagnostics: SUPPORT.md
• Security reporting: SECURITY.md
• License: LICENSE