CPU schedulers with sched_ext

sched_ext lets you run alternative CPU schedulers on Linux. A CPU scheduler decides how processor time is shared between applications. Different schedulers can change how your system responds under load.

This guide covers running sched_ext schedulers on Devario using packages from the Devario repositories: how to install them, choose a scheduler with the scxtui terminal interface or the scxcli command-line tool, and check what is running. Service configuration and custom profiles are covered in Advanced usage.

Install the tools

Choose a package

Prefer scx-scheds, the release package, for everyday use when it provides the tools you need. scx-scheds-git follows development rather than a release. It is not the stable version, and updates can introduce regressions. Choose one package, not both.

The switching instructions below need scxcli, scxtui and scx.service. The Devario scx repositories currently publish these in scx-scheds-git; they do not publish a separate scx-scheds release package. The Git package also declares that it provides scx-scheds, but that does not make it a stable release. Check the package listing before installing.

On Arch, the release package is available from the distribution repositories. Older releases do not include this switching interface, so their setup instructions differ.

Install sched_ext from Devario repos

1. Choose one scx repository. Follow its setup page for the signing key, repository configuration and synchronization commands. Do not enable both.

   • devario-scx: upstream main, without extra scheduler backports. Use this if you do not need to test backports.
   • devario-scx-dev: adds scheduler backports not yet merged upstream. Also offers linux-devario-dev. Use this for testing.

   Neither repository is a stable release channel. Both contain Git builds. On Devario, use Shelly and /etc/shelly.conf; see native repository configuration. The pacman instructions are for an Arch-based installation using pacman.

2. Update your system and install scx-scheds-git.

   Shelly (Devario)

   shelly upgrade standard
   shelly install standard scx-scheds-git polkit

   pacman (Arch-based)

   sudo pacman -Syu scx-scheds-git polkit

   On Arch-based systems, this package conflicts with scx-scheds. Review the replacement prompt before proceeding.

   The package includes the schedulers, scxcli, scxtui, the scxtop monitor, and the service and policy files they use. You do not need scx-tools-git for this guide.

   polkit supplies pkexec, which the tools need for switching as a normal user. It may already be installed with your desktop.

3. Check your running kernel and the tools.

   test -d /sys/kernel/sched_ext && echo "sched_ext available"
   scxcli get

   The first command should print sched_ext available. If it does not, boot a kernel with sched_ext support, such as a Devario kernel, before continuing. state: default (kernel scheduler) is normal when no scx scheduler is running.

If you want the release package on Arch instead, use the distribution repositories, without adding a Devario scx repository:

sudo pacman -Syu scx-scheds

Check that your installed release includes scxcli and scxtui before following the switching steps below. If it does not, use the setup documented for that release, or choose the Git build if you want to test the newer tools.

Use one scheduler manager

If you already use scx_loader.service, disable and stop it before starting a scheduler here: sudo systemctl disable --now scx_loader.service. Do not run it alongside scx.service. The optional scx-tools-git package is for applications that still need the separate scx-loader D-Bus interface.

Switch schedulers

Use scxtui

Open a terminal as your normal desktop user and run:

scxtui

1. Use ↑ / ↓ to choose an entry in the recommended list.
2. Press Enter to start it, or to switch from the scheduler already running.
3. Check the status panel to confirm the scheduler is running.
4. Press q to close the menu. The scheduler keeps running.

Your selection also starts at boot.

Switching normally needs no password in an active local session with pkexec and the packaged polkit policy. Remote sessions and local administrator policies can require authentication.

Task	In scxtui
Return to the kernel scheduler and keep that choice after reboot	Select Default, then press Enter.
Pause the selected scheduler without forgetting it	Press s. It can start again at the next boot.
Resume a paused scheduler	Select its entry and press Enter.
Browse more installed schedulers	Press A to toggle the full list.
Read the service log	Press l, then q to return.
Refresh the display	Press R.

Default and stop are different: Default disables the scx service; stopping it keeps the selected scheduler and its boot setting.

Use the command line

List the recommended entries and check what is running:

scxcli list
scxcli get

Start a scheduler by the ID shown in the list. For example:

pkexec scxcli start scx_lavd
scxcli get

To switch, run start again with another listed ID. The new selection takes effect immediately and persists after reboot. To pause that selection and resume it later:

pkexec scxcli stop
pkexec scxcli start

To return to the kernel scheduler and disable scx at boot instead:

pkexec scxcli start default

Default clears the saved selection. To use scx again afterwards, choose an entry with start ID. Running start without an ID cannot restore a cleared selection.

Read-only commands do not need pkexec. Commands that change the scheduler need root privileges; pkexec applies the installed polkit policy.

Which scheduler should I try?

You can keep Default if your system already behaves well. A different scheduler is not automatically faster, and one unsuited to your workload can perform worse.

Start with the descriptions in scxtui or scxcli list:

Entry	What it is intended for
Default	The kernel’s built-in scheduler; also your baseline for comparison.
Cosmos (scx_cosmos)	Keeping the system responsive under load.
LAVD (scx_lavd)	Prioritizing tasks that need a quick response.
EEVDF (scx_eevdf)	Trying newer kernel scheduler updates without upgrading the kernel.
Cake (scx_cake)	Gaming responsiveness.

Availability and recommendations depend on your installed build and catalog. Use the installed list rather than assuming every entry above is present.

Change one thing at a time and compare the same game, application or workload against Default. Keep the option that works better on your hardware. The full list marks featured, stable, experimental, and not in the catalog entries; these labels are guidance, not a promise of better performance.

Advanced usage

For custom options, service configuration or troubleshooting. You do not need these steps to switch schedulers.

Service and configuration

sched_ext runs a CPU scheduler as a BPF program. The running kernel must have CONFIG_SCHED_CLASS_EXT=y; /sys/kernel/sched_ext exposes its state. Only one scx scheduler can be attached at a time. When it exits, the kernel returns to its own scheduler.

scxtui delegates changes to scxcli, which configures scx.service. This path does not use a separate daemon or D-Bus. The optional scx_loader is a different manager, not a dependency.

The persistent selection is in /etc/default/scx, for example:

/etc/default/scx

SCX_SCHEDULER=/usr/bin/scx_lavd
SCX_FLAGS=""

scxcli manages these two keys and preserves other lines. Prefer switching through scxtui or scxcli; hand-written flags may not be accepted by the password-free resume command. The package preserves this configuration during upgrades.

Useful read-only diagnostics:

scxcli get
systemctl status scx.service
journalctl -u scx.service -b 0

In scxcli get, state reflects the kernel, running describes the service process, and configured describes what the next start would run. They can differ after a manual edit, failed start or scheduler launched outside the service. scxcli get --json exposes the status for scripts.

Custom options and profiles

start ID uses the defaults or an administrator-approved catalog profile. Use run to supply your own scheduler options; it requires administrator authentication. For example:

pkexec scxcli run scx_lavd --performance

run also saves the configuration and enables the service at boot; it is not a temporary test. Restore a listed entry with start ID when you finish testing. Run scx_lavd --help to check the options supported by your installed version.

To make custom options selectable through scxtui, an administrator can add a named profile to the catalog:

scxcli catalog show > catalog.json
# Edit the exported catalog, then install it:
sudo scxcli catalog save < catalog.json

The shipped catalog is /usr/share/scx/catalog.json. An override at /etc/scx/catalog.json replaces the whole shipped file, rather than merging with it, and does not automatically pick up later upstream recommendations. Keep it owned by root and not writable by other users. Saving validates the catalog but does not restart a scheduler; start the changed profile again.

Preview a file before installing it:

scxcli list all --catalog ./catalog.json
scxtui --catalog ./catalog.json

Previewing does not authorize new profiles: starting still uses the installed catalog. To remove the override and return to the shipped catalog:

sudo scxcli catalog reset

Temporary service overrides

For service-level testing without editing /etc/default/scx, set an override, then restart the service:

sudo systemctl set-environment SCX_SCHEDULER_OVERRIDE=scx_lavd
sudo systemctl set-environment SCX_FLAGS_OVERRIDE="--performance"
sudo systemctl restart scx.service

Clear both overrides and restart to restore the saved configuration:

sudo systemctl unset-environment SCX_SCHEDULER_OVERRIDE SCX_FLAGS_OVERRIDE
sudo systemctl restart scx.service

scxcli get and scxtui report active overrides. A subsequent scxcli start ID clears them as part of selecting that entry.

Troubleshooting

Problem	What to check
No sched_ext available message, or the service is skipped	The running kernel needs sched_ext support. Boot a suitable Devario kernel; installing tools alone does not add kernel support.
A scheduler fails to start	Read scxcli get and journalctl -u scx.service -b 0. The service stops retrying after two startup failures in 30 seconds. A new start ID resets the failed state before retrying.
Switching asks for a password	Check that scxcli is installed at /usr/bin/scxcli and that /usr/share/polkit-1/actions/org.sched_ext.scxcli.policy is installed. A local policy or a non-console session can also require authentication.
Resume refuses custom SCX_FLAGS	Use pkexec scxcli start ID to select a listed entry, or repeat the administrator-authorized run command. Password-free resume accepts only options matching an approved profile.
A scheduler is missing from the list	Try scxcli list all. Some schedulers are deliberately hidden because they need their own configuration; use an administrator profile or run with the required options.
Every command refuses the custom catalog	The override may be invalid, unreadable, a symlink, or incorrectly owned. Correct it, or use sudo scxcli catalog reset to remove the override.
Configured and running schedulers differ	Check for active overrides, another scheduler manager, a failed start, or a scheduler launched manually. Do not start a second manager to fix the mismatch.

For help, include the package version, running kernel, scxcli get output and relevant service log. Review logs for personal information before sharing them.

Developer references

This page adapts the sched_ext guide for Devario by sir_lucjan. It describes the upstream scx.service / scxcli / scxtui workflow checked at commit c0347f11c. Older packages or other distributions may still use scx-loader instead.

• scxcli reference: commands, privileges and custom profiles.
• scxtui reference: requirements, keyboard controls and interface behavior.
• Catalog contract: schema, trust rules, status detection and client integration.
• Scheduler descriptions: individual schedulers and their intended workloads.
• Upstream installation: source builds and other distributions. A tools-only build does not install scheduler binaries.
• Seafoam Labs scx fork: Devario integration and scheduler development.
• Devario package recipes: package contents and build configuration.