Round Robin Scheduling (CLASS_RR)

The optional CLASS_RR scheduling class is available only within the SCHED_CLASS scheduler. It is similar to SCHED_FIFO but implements a priority-based, preemptive policy with round-robin time slicing based on a configurable time quantum. Priority of threads may vary from K_RR_PRIOMAX (0, highest priority) to K_RR_PRIOMIN (255, lowest priority). CLASS_RR uses the full range of priorities (256) of the SCHED_CLASS scheduler.

The SCHED_RR policy is similar to the SCHED_FIFO policy, except that an elected thread is given a fixed time quantum. If the thread is still running at quantum expiration, it is placed at the end of its priority ready queue, and then may be preempted by threads of equal priority. The thread's quantum is reset when the thread becomes ready after being blocked. It is not reset when the thread is elected again after a preemption. The time quantum is the same for all priority levels and all threads. It is defined by the K_RR_QUANTUM value (100 milliseconds).

For details, see the ROUND_ROBIN(5FEA) man page.