Problem 2. In addition to ordinary round-robin scheduling, consider the followin

Question

Problem 2. In addition to ordinary round-robin scheduling, consider the following two
variations:
Selfish Round-Robin: There is a maximum number of processes that can be in the round-
robin queue. After that maximum is reached, newly entering processes are placed in a
holding queue, where they do not get any access to the CPU. When a process in the
round-robin queue completes and leaves the system, the oldest process in the holding
queue is moved to the round-robin queue.
Priority Round-Robin: Each process has a priority in the range 1-10, where 10 is the best.
When a process is given a time slice, the quantum equals some basic constant (say 50ms)
times the process’s priority.
Compare the behavior of these three scheduling disciplines in a system that is very heavily
loaded. How are short, medium and large jobs affected?

Explanation / Answer

Dear user, Ordinary round robin: In an ordinary round robin scheduling, all the processes are assigned with some equal slices of time. So all the processes are equally prioritized. In this type of scheduling, the larger jobs can be more benefited than the shorter jobs as they are given more number of time slices. But the shorter jobs, though they need less time, they may have to wait until its turn comes. It does not have much impact on the medium size jobs. Selfish Round-Robin: This scheduling process can be effective (useful) for shorter jobs than for medium and large size jobs. As the shorter jobs can be completed fast, all the other jobs can be executed faster. But for larger and medium size jobs, as they take large amount of time, the processes in the holding queue have to wait for a long time to enter into round robin queue. Priority Round-Robin: In this scheduling process, the smaller processes can be more benefited than the larger jobs. A larger job with lowest priority takes more time for completion and the other processes needs to wait for a long time. If smaller processes are considered, even if their priority is low, they can be completed with in shorter time as they are small. Medium jobs may not have much affect in this scheduling.

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