What is Round-Robin Scheduling?
Round-robin scheduling is an algorithm used to assist in creating process or job schedules to ensure that each process required to complete a job gets an ample amount of run time. CPUs in computers can use time slicing to provide a set amount of time for each process to use per cycle. Using round-robin scheduling allots a slice of time to each process that is running. In a computer for example, the user starts three applications, Email, a web browser, and a word processor. These applications are loaded into system memory as processes and each is allowed to run without the user considering which applications are running in the background. Round-robin scheduling handles the sharing of resources between the three application processes (and the countless others running in the background completely invisible to the user). This scheduling works well because each application gets a certain amount of time per processor cycle. A processor cycle is the amount of time it takes the CPU to manage e
It is one of the oldest, simplest, fairest and most widely used scheduling algorithms, designed especially for time-sharing systems. A small unit of time, called timeslice or quantum, is defined. All runnable processes are kept in a circular queue. The CPU scheduler goes around this queue, allocating the CPU to each process for a time interval of one quantum. New processes are added to the tail of the queue. The CPU scheduler picks the first process from the queue, sets a timer to interrupt after one quantum, and dispatches the process. If the process is still running at the end of the quantum, the CPU is preempted and the process is added to the tail of the queue. If the process finishes before the end of the quantum, the process itself releases the CPU voluntarily. In either case, the CPU scheduler assigns the CPU to the next process in the ready queue. Every time a process is granted the CPU, a context switch occurs, which adds overhead to the process execution time.
Each job is given a time quantum slice to run; if not completely done by that time interval, job is suspended and another job is continued. After all other jobs have been given a quantum, ?rst job gets its chance again. True or False: Round-robin scheduling is preemptive. Answer: True. What is the time quantum used for? Answer: Round-robin scheduling, to give each process the same processing time. How should the time quantum be related to the context switch time? Answer: Quantum should be very large compared to context switch time. How should the time quantum be related to the CPU burst times? Answer: 80% of CPU bursts should be shorter than time quantum. Describe the foreground-background approach. Answer: Low priority processes run in background; high priority jobs run in foreground; background runs only when foreground is empty, or waiting for I/O. How can multilevel queues be scheduled? Which might have priority over others? Answer: Each queue can have absolute priority over lower
