Part of CachyOS Wiki Notes. From the official CachyOS wiki (last updated 2026-09-07).

sched-ext Schedulers

sched-ext (Extensible Scheduler Class) is a Linux kernel feature for implementing thread schedulers in BPF and loading them dynamically — you swap schedulers from userspace without building a new kernel.

Running any sched-ext scheduler temporarily detaches the default kernel scheduler (EEVDF or BORE); stopping it hands control back.

Packages

Schedulers come from scx-scheds / scx-scheds-git:

# Stable branch + scx_loader and scxctl tools
sudo pacman -S scx-scheds scx-tools
 
# Bleeding edge + tools
sudo pacman -S scx-scheds-git scx-tools-git

scx-scheds-git may not include every experimental scheduler (some live in unmerged feature branches). Both scxctl and scx_loader need admin rights (sudo, or a polkit agent that prompts).

Run one from a terminal

sudo scx_rusty

CTRL + C stops it and the default scheduler takes over again.

scxctl (runtime control, needs a working polkit agent)

scxctl start --sched flash --mode gaming
scxctl stop
scxctl restore
scxctl switch --sched bpfland --mode gaming
scxctl start --sched cosmos --args="-c,75,-m,0-15"
scxctl switch --sched flash --args="-s,20000"

Arguments are comma-separated, e.g. --args="-c,75,-m,0-15" is argument,value pairs. Subcommands: get, list, start, switch, stop, restart, restore. scxctl restore returns to the default scheduler from the config file.

scx_loader D-Bus interface

dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.scx.Loader.StartScheduler string:scx_rusty uint32:0

Mode numbers: 0 = default scheduler flags, 1 = Gaming, 2 = Power Saving, 3 = Low Latency, 4 = Server. Other methods: StartSchedulerWithArgs, StopScheduler, RestoreDefault, SwitchScheduler, SwitchSchedulerWithArgs, plus property reads CurrentScheduler / SupportedSchedulers.

Setting a default scheduler at boot

sudo mkdir -p /etc/scx_loader
sudo cp /usr/share/scx_loader/config.toml /etc/scx_loader/config.toml
sudo nano /etc/scx_loader/config.toml

Set default_sched = "scx_pandemonium", default_mode = "Auto", then:

sudo systemctl enable --now scx_loader.service

Config lookup order: /etc/scx_loader/config.toml (preferred) → /etc/scx_loader.toml → /usr/share/scx_loader/config.toml → /usr/share/scx_loader.toml. Per-scheduler arguments go under a [scheds.scx_name] section.

Gotcha: do not run scx_loader.service alongside scx.service — the loader starts but does nothing.

systemctl disable --now scx.service && systemctl enable --now scx_loader.service
systemctl restart scx_loader.service

The old scx.service (SCX_SCHEDULER=, SCX_FLAGS=) maps to default_sched = "scx_lavd" / default_mode = "Auto" plus [scheds.scx_lavd] with auto_mode = ["--performance"]. The Kernel Manager GUI handles the transition unless you had custom flags in /etc/default/scx — see CachyOS Kernel Manager.

Debugging

systemctl status scx_loader.service
journalctl -u scx_loader.service
journalctl -u scx_loader.service -b 0

ananicy-cpp usually coexists fine; disable it as a troubleshooting step for stalls: systemctl disable --now ananicy-cpp.

Power-profile switching (patched power-profiles-daemon): Power Saver → Power Save, Balanced → Auto, Performance → Gaming. The game-performance wrapper switches to Gaming on game launch and reverts on close.

Benchmarking

sudo pacman -S cachyos-benchmarker
cachyos-benchmarker ~/cachyos-benchmarker/
 
sudo pacman -S schbench
schbench -m 2 -t 8 -r 60

Crash log:

journalctl --unit scx_loader.service --boot 0 > crash.log

Schedulers documented on the page

scx_beerland, scx_bpfland, scx_cake, scx_cosmos, scx_flash, scx_flow, scx_forge, scx_lavd, scx_pandemonium, scx_p2dq, scx_tickless, scx_rustland, scx_rusty.

Each scheduler lists per-mode flags where it has them; use scx_<schedulername> --help for the real list. No modes are listed for scx_beerland (“none for the moment”), scx_cake, scx_forge, scx_rustland or scx_rusty. Example flags: bpfland Low Latency -m performance -w, Power Save -s 20000 -m powersave -I 100 -t 100; cosmos Gaming -s 700 -S; LAVD --performance / --powersave (plus scx_lavd --autopower); p2dq Gaming --task-slice true -f --sched-mode performance. scx_flow has no Gaming/Power Save/Low Latency modes.

Related: CachyOS Kernels (BORE/EEVDF/BMQ variants), CachyOS Kernel Manager.