Round-Robin (RR) Scheduling

In this topic, you will learn about, Round-Robin scheduling.

Round-Robin (RR) Scheduling:

The Round-Robin scheduling algorithm is designed especially for the time-sharing systems. It is similar to FCFS, but preemption is added to switch between processes a small unit of time, called time Quantum or Time Slice is defined. A time Quantum is generally 10-100 milliseconds. The ready queue is treated as a circular queue. The CPU scheduler circular goes around the ready queue allocating the CPU for each process for a time interval of up to one-time quantum.

To implement Round-Robin scheduling, we keep the ready queue as a FIFO queue of processes. The CPU scheduler picks the first process from the ready queue, shakes the timer to interrupt after 1 quantum and dispatches a process.

In Round-Robin scheduling, one of two things will then happen:

  1. The process may have a CPU burst of less than 1-time quantum. In this case, the process itself will release the CPU voluntarily. The scheduler will then proceed to the next process, otherwise
  2. If the CPU burst of the currently running process is longer than one-time quantum, the timer will go off and will cause an interrupt to the Operating System (OS).

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See also  Multiple Processor scheduling