scx_loader: A DBUS Interface for Managing sched-ext Schedulers

scx_loader is a utility that provides a convenient DBUS interface for starting, stopping, and managing sched_ext schedulers.

Features

• StartScheduler Method: Launches a scheduler specified by its scx_name (e.g., "scx_rusty") and a scheduler mode (profile) represented as an unsigned integer.
• StartSchedulerWithArgs Method: Starts a scheduler with its scx_name and allows passing arbitrary CLI arguments directly to the scheduler.
• StopScheduler Method: Terminates the currently running scheduler.
• SwitchScheduler Method: Stops the current scheduler and starts the specified scheduler with the given mode.
• SwitchSchedulerWithArgs Method: Stops the current scheduler and starts the specified scheduler with the provided arguments.
• CurrentScheduler Property: Returns the scx_name of the active scheduler or "unknown" if none is running.
• SchedulerMode Property: Provides information about the currently active scheduler's mode (profile).
• SupportedSchedulers Property: Lists the schedulers currently supported by scx_loader.

Usage

scx_loader interacts with schedulers through its DBUS interface. You can use tools like dbus-send or gdbus to communicate with it.

Examples using dbus-send:

• Start a Scheduler:

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

  (This starts scx_rusty with scheduler mode 0)

• Start a Scheduler with Arguments:

  dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.scx.Loader.StartSchedulerWithArgs string:scx_bpfland array:string:"-k","-c","0"
  

  (This starts scx_bpfland with arguments -k -c 0)

• Stop the Current Scheduler:

  dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.scx.Loader.StopScheduler
  

• Switch Scheduler:

  dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.scx.Loader.SwitchScheduler string:scx_lavd uint32:2
  

  (This switches to scx_lavd with scheduler mode 2)

• Switch Scheduler with Arguments:

  dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.scx.Loader.SwitchSchedulerWithArgs string:scx_bpfland array:string:"-k","-c","0"
  

  (This switches to scx_bpfland with arguments -k -c 0)

• Get the Currently Active Scheduler:

  dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.freedesktop.DBus.Properties.Get string:org.scx.Loader string:CurrentScheduler
  

• Get the Supported Schedulers:

  dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.freedesktop.DBus.Properties.Get string:org.scx.Loader string:SupportedSchedulers
  

Note: Replace the example scheduler names and arguments with the actual ones you want to use.

DBUS and Systemd Service

scx_loader provides the org.scx.Loader DBUS service and is automatically started by dbus-daemon when an application calls into this service. Users and administrators do not need to manually start the scx_loader daemon.

scx_loader is managed by the scx_loader.service systemd unit. This service is distinct from the scx.service unit, which is used to manage schedulers directly (without DBUS).

Debugging

In case of issues with scx_loader, you can debug the service using the following steps:

1. Check the service status:

   systemctl status scx_loader.service
   

2. View the service logs:

   journalctl -u scx_loader.service
   

3. Enable debug logging: You can temporarily enable debug logging by modifying the systemd service file:

   • Edit the service file:

     sudo systemctl edit scx_loader.service
     

   • Add the following lines under the [Service] section:

     Environment=RUST_LOG=trace
     

   • Restart the service:

     sudo systemctl restart scx_loader.service
     

   • Check the logs again for detailed debugging information.

D-Bus Introspection XML

scx_loader provides a D-Bus Introspection XML file that describes its interface. This file can be used by language bindings and tools to interact with the service.

Using the Introspection XML:

The introspection XML can be accessed in two ways:

1. Through the D-Bus introspection interface:

   dbus-send --system --print-reply --dest=org.scx.Loader /org/scx/Loader org.freedesktop.DBus.Introspectable.Introspect
   

   This will output the XML describing the scx_loader interface.

2. From the project repository:

   The XML file is also available in the provided file org.scx.Loader.xml.

You can then use this XML with tools like gdbus-codegen or other language-specific D-Bus bindings to generate code that interacts with scx_loader.

For example, with gdbus-codegen, you can generate C code for the interface:

gdbus-codegen --generate-c-code scx-loader-bindings org.scx.Loader.xml

This will produce header and source files that you can use to interact with scx_loader from your C code.

Development Status

scx_loader is under active development. Future improvements may include:

• More robust error handling.
• Configuration file.