Introduce scx_flash (Fair Latency-Aware ScHeduler), a scheduler that
focuses on ensuring fairness among tasks and performance predictability.
This scheduler is introduced as a replacement of the "lowlatency" mode
in scx_bpfland, that has been dropped in commit 78101e4 ("scx_bpfland:
drop lowlatency mode and the priority DSQ").
scx_flash operates based on an EDF (Earliest Deadline First) policy,
where each task is assigned a latency weight. This weight is adjusted
dynamically, influenced by the task's static weight and how often it
releases the CPU before its full assigned time slice is used: tasks that
release the CPU early receive a higher latency weight, granting them
a higher priority over tasks that fully use their time slice.
The combination of dynamic latency weights and EDF scheduling ensures
responsive and stable performance, even in overcommitted systems, making
the scheduler particularly well-suited for latency-sensitive workloads,
such as multimedia or real-time audio processing.
Tested-by: Peter Jung <ptr1337@cachyos.org>
Tested-by: Piotr Gorski <piotrgorski@cachyos.org>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Add a small section to document how to use SCX_SCHEDULER_OVERRIDE and
SCX_FLAGS_OVERRIDE with the scx systemd service.
Also fix a small typo (namspace -> namespace).
Signed-off-by: Pietro Righi <pietro.righi.email@gmail.com>
Switching the scheduler requires changing SCX_SCHEDULER (and potentially
also SCX_FLAGS) in /etc/default/scx.
This patch allows overriding these settings using systemd environment
variables SCX_SCHEDULER_OVERRIDE and SCX_FLAGS_OVERRIDE, without
changing the default configuration.
Example:
> grep SCX_SCHEDULER /etc/default/scx
SCX_SCHEDULER=scx_rusty
> sudo systemctl status scx
...
Main PID: 8021 (scx_rusty)
...
> sudo systemctl set-environment SCX_SCHEDULER_OVERRIDE=scx_rustland
> sudo systemctl restart scx
> sudo systemctl status scx
...
Main PID: 4021 (scx_rustland)
...
This feature can be useful for quickly testing different schedulers and
settings, without altering the global system configuration.
Signed-off-by: Pietro Righi <pietro.righi.email@gmail.com>
Currently if the scx.service is failing to launch due issues, systemd will try to start the scheduler all the time.
This results into a massive flood to the kernel and does not bring the service up again.
explanation of the changes:
The StartLimitBurst=2 and StartLimitIntervalSec=30 settings tell systemd that if the service unsuccessfully tries to restart itself twice within 30 seconds, it should enter a failed state and no longer try to restart. This ensures that if the service is truly broken, systemd won't continuously try to restart it.
Signed-off-by: Peter Jung <admin@ptr1337.dev>
