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Round Robin Scheduling – a type of scheduling algorithm

Round Robin Scheduling algorithms fall under the category of best effort scheduling algorithms. Along with round robin there are many other algorithms such as the following:
– A max min fair scheduling algorithm or simple fair queuing
– Proportionally fair scheduling
– Weighted fair queuing

What is Round Robin Scheduling?

– In this scheduling type, a fixed time unit is assigned by the scheduler to each of the processes and then the processes are put in to cycles.
– This algorithm involves a major overhead especially when the time unit per process is small.
– The throughput offered by the round robin scheduling is intermediate between that of the shortest job first and first come first served scheduling algorithms.
– FCFS is capable of completing shorter jobs quickly whereas the SJF can complete the longer processes in less time.
– The average response of this scheduling has been observed to be poor.
– Also, the numbers of processes determine the waiting rather than the average length of the process.
– A system which purely involves round robin scheduling is rarely able to meet the deadlines.
– This is all because of the high waiting times.

– In this scheduling algorithm, no process is assigned any priority and therefore there are no possibilities of starvation.
– The time unit is allocated to the processes based up on the order in which they arrive i.e., in a way similar to the FCFS (first come first served).
– This is the simplest scheduling algorithms that could be employed for an efficient operating system.
– All the processes are assigned time slices in equal portions in an order that is circular.
– This way of handling processes without assigning them priority is called cyclic executive.
– This scheduling algorithm is so easy in implementation and free of any possible starvation, all because of its simplicity.
– Many other scheduling problems such as that of the data packet scheduling can also benefit from round robin scheduling in the networks.
– Round robin principle is employed in other fields and so the name for this type of scheduling has been given.
– In general as per this principle, each person gets an equal share of one thing in return for the other.
– For a fair scheduling of the processes, time sharing is employed by a round robin scheduler.
– The time slot given to each of the processes is commonly known as the quantum.
– If the processor is unable to finish executing a job in the given time, it is interrupted and another job is handed over to the CPU.
– The job that could not be completed this time is again assigned a time slot.
– If time sharing is not used because of the quantum being much larger when compared to the size of the job, the process that would be favored will be the one that produces larger jobs.
– An alternative approach would be the division of all the processes in to equal number of time units of size proportional to that of the process.
– This will ensure that all the processes end together.
– Round robin scheduling proves to be a great alternative to the FCFS algorithm when it comes to statistical multiplexing as in best effort packet switching.
– A router, multiplexer or a switch following the round robin scheduling maintains a separate queue for all the data flows.
– The identification of the data is done by the address of its source and destination.
– In this algorithm, every active data flow consisting of data packets in the queue can make turns in a repeated order for transferring packets on to a data channel that is shared.
– This scheduling algorithm conserves the work i.e., it avoids the link resources from being unused as far as possible.
– Round robin scheduling is not fair enough when it comes to scheduling jobs where the size of the data packets vary considerably.
– In such cases fair queuing can be considered.

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