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Os 3

CPU scheduling determines which process receives CPU time from the ready queue, involving long-term, short-term, and medium-term schedulers. Various scheduling criteria include CPU utilization, throughput, turnaround time, waiting time, response time, and fairness, with algorithms such as FCFS, SJN, SRTF, RR, priority scheduling, multi-level queue, and multi-level feedback queue. Each algorithm has its advantages and disadvantages, impacting process execution and resource allocation.

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6 views2 pages

Os 3

CPU scheduling determines which process receives CPU time from the ready queue, involving long-term, short-term, and medium-term schedulers. Various scheduling criteria include CPU utilization, throughput, turnaround time, waiting time, response time, and fairness, with algorithms such as FCFS, SJN, SRTF, RR, priority scheduling, multi-level queue, and multi-level feedback queue. Each algorithm has its advantages and disadvantages, impacting process execution and resource allocation.

Uploaded by

deder50551
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We take content rights seriously. If you suspect this is your content, claim it here.
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Unit 3: CPU Scheduling

1. CPU Scheduling Basics

 CPU Scheduling decides which process gets the CPU when mul ple processes are in the
ready queue.

 Scheduler selects one of the ready processes to execute.

 Dispatcher gives control of the CPU to the selected process.

2. Types of Schedulers

 Long-term Scheduler – Controls degree of mul programming.

 Short-term Scheduler – Selects a process from the ready queue.

 Medium-term Scheduler – Suspends/resumes processes.

3. Scheduling Criteria

 CPU U liza on: Keep CPU as busy as possible.

 Throughput: No. of processes completed per me unit.

 Turnaround Time: Time from submission to comple on.

 Wai ng Time: Time spent in the ready queue.

 Response Time: Time from request submission to the first response.

 Fairness: Equal opportunity to all processes.

4. Scheduling Algorithms

a) First-Come, First-Served (FCFS)

 Non-preemp ve

 Processes served in order of arrival.

 Simple but can lead to convoy effect.

b) Shortest Job Next (SJN) / Shortest Job First (SJF)

 Non-preemp ve

 Process with the shortest burst me is scheduled first.

 Op mal in terms of average wai ng me.

 Can cause starva on.


c) Shortest Remaining Time First (SRTF)

 Preemp ve version of SJF.

 Always selects process with the shortest remaining me.

d) Round Robin (RR)

 Preemp ve

 Each process gets a fixed me quantum.

 Suitable for me-sharing systems.

e) Priority Scheduling

 Each process has a priority. The CPU is assigned to the highest-priority process.

 Can be preemp ve or non-preemp ve.

 Low priority processes may starve.

 Aging technique avoids starva on.

f) Mul level Queue Scheduling

 Separate queues for different types of processes (e.g., interac ve, batch).

 Each queue has its own scheduling algorithm.

 Fixed priority or round-robin among queues.

g) Mul level Feedback Queue Scheduling

 A process can move between queues.

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