Real-Time Scheduling Policies
The kernel contains the following real-time scheduling policy implementations:
PFAIR, an implementation of the PD2 algorithm,
PSN-EDF, a partitioned EDF (P-EDF) implementation with support for the real-time locking protocols,
GSN-EDF, a global EDF (G-EDF) implementation with support for real-time locking protocols,
C-EDF (Clustered EDF), a hybrid of G-EDF and P-EDF, and
Linux, a placeholder policy that disables all real-time functionality added by the LITMUSRT patch.
Only one policy can be active at any time. Initially (i.e., during and after boot), the Linux policy is active. You can use the tool showsched (part of liblitmus) to display the name of the currently active policy.
Changing the Active Policy
You can use the tool setsched (part of liblitmus) to select a new plugin at run time. Only root can change the active policy, and only when there are no real-time tasks present.
The script setsched depends on the dialog utility. If you do not have the dialog utility installed, then you can still use setsched by passing the desired scheduling policy as a command line parameter. For example, type setsched PFAIR to activate the PFAIR plugin.
The list of loaded plugins is exported as /proc/litmus/plugins/loaded; the active plugin is reported as /proc/litmus/active_plugin.