The Real Time Scheduling Class
As mandated by the POSIX standard, Linux supports two real-time scheduling classes in addition to "normal" processes. The structure of the scheduler enables real-time processes to be integrated into the kernel without any changes in the core scheduler — this is a definitive advantage of scheduling classes.31
Now is a good place to recall some of the facts discussed a long time ago. Real-time processes can be identified by the fact that they have a higher priority than normal processes — accordingly, their static_prio value is always lower than that of normal processes, as shown in Figure 2-14. The rt_task macro is
31 The completely fair scheduler needs to be aware of real-time processes in the wake-up preemption code, but this requires only very little effort.
task_struct *p) = cfs_rq->curr, provided to establish whether a given task is a real-time process or not by inspecting its priority, and task_has_rt_policy checks if the process is associated with a real-time scheduling policy.
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