Round Robin Scheduling in Operating Systems

Round Robin Scheduling is a CPU scheduling algorithm used in operating systems to manage the execution time of multiple processes competing for CPU resources. It is named "round robin" because the CPU cycles through each process, allocating a fixed time slice or "quantum" to each process.

Key Characteristics

• Equal Opportunity: Each process is given an equal chance to execute.
• Time Quantum: A fixed amount of CPU time assigned to each process.
• Fairness: Ensures fairness among all processes.

Process Flow

1. Process Arrival: Processes enter the system queue.
2. Time Allocation: Each process receives a predefined quantum of CPU time.
3. Execution: The process utilizes the CPU for the allocated quantum.
4. Rotation: If a process is incomplete after its quantum, it is moved to the end of the queue.
5. Repeat: The CPU continues cycling through the queue until all processes are completed.

Advantages

• Fairness: Equal CPU time for each process.
• Simplicity: Straightforward and easy to implement.
• Responsiveness: Handles multiple processes effectively in time-sharing systems.

Disadvantages

• Overhead: High overhead due to frequent context switches.
• Underutilization: Large quantum can lead to CPU idleness.

Scenario Examples

Scenario 1: Processes with Same Arrival Time

• Processes: P1, P2, P3
• Quantum: 2 ms
• Execution Order:
  • P1 executes for 2 ms
  • P2 executes for 2 ms
  • P3 executes for 2 ms
  • P1 completes after another 2 ms
  • P2 executes for 2 ms, then completes
  • P3 completes
• Average Turnaround Time: 10.33 ms
• Average Waiting Time: 6.33 ms

Scenario 2: Processes with Different Arrival Times

• Processes: P1, P2, P3
• Quantum: 2 ms
• Execution Order:
  • P1 executes until P2 arrives
  • P2 executes
  • P1 continues
  • P3 executes
  • Processes complete in order
• Average Turnaround Time: 5 ms
• Average Waiting Time: 1 ms

Conclusion

Round Robin Scheduling is an effective method for ensuring fairness and simplicity in CPU scheduling. It requires a well-chosen quantum to minimize overhead while maintaining responsiveness. Despite the potential for increased overhead, it remains a preferred choice for systems requiring balanced process management.

Code Implementations

• Program for same arrival time: Link
• Program for different arrival times: Link