CPU Scheduling Concepts

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Questions and Answers

What is the primary characteristic of the Round Robin scheduling algorithm?

Each process receives a small, fixed unit of CPU time before being preempted. (correct)

Processes are arranged in a queue based solely on their burst time.

It prioritizes processes based on their arrival time.

Each process runs until completion before the next process starts.

What happens to a process in the Round Robin queue after its time quantum expires?

It is terminated.

It is moved to a waiting state until it is called again.

It resumes execution immediately.

It is added back to the end of the ready queue. (correct)

In a Preemptive Priority scheduling algorithm, what dictates which process continues to run?

The burst time of the processes.

The entry time of the processes into the queue.

The priority level of the processes. (correct)

The time quantum of the CPU.

Which of the following best describes the effect of a small time quantum in a Round Robin scheduling?

It can increase the overhead due to frequent context switching. Signup and view all the answers

How does the average turnaround time of Round Robin compare to that of Shortest Job First (SJF) scheduling?

Round Robin typically has a higher average turnaround time than SJF. Signup and view all the answers

What is the main purpose of a CPU scheduler?

To allocate the CPU to processes that are ready to execute Signup and view all the answers

In which scenario does nonpreemptive scheduling occur?

When a process completes its CPU burst Signup and view all the answers

Which of the following best describes dispatch latency?

Time required for the dispatcher to stop one process and start another Signup and view all the answers

How does the CPU-I/O burst cycle affect process execution?

It alternates between periods of CPU execution and waiting for I/O Signup and view all the answers

Which scheduling decision is considered preemptive?

Switching a process from running to ready Signup and view all the answers

What is one of the main criteria used to evaluate scheduling algorithms?

Fairness among processes Signup and view all the answers

Which component is responsible for giving control of the CPU to the selected process?

The dispatcher module Signup and view all the answers

In a multiprogramming operating system, what is primarily optimized?

CPU utilization through overlapping I/O and computation Signup and view all the answers

What is the main goal of maximizing CPU utilization?

To keep the CPU as busy as possible Signup and view all the answers

Which scheduling criterion refers to the total time taken to complete a process from submission to completion?

Turnaround time Signup and view all the answers

In the First-Come, First-Served (FCFS) scheduling example, what was the average waiting time for the processes P1, P2, and P3 when they arrived in the order P1, P2, P3?

17 Signup and view all the answers

What effect is primarily illustrated when a short process is placed behind a long process in FCFS scheduling?

Convoy effect Signup and view all the answers

What is the key characteristic of nonpreemptive Shortest-Job-First (SJF) scheduling?

A process cannot be preempted once it starts executing Signup and view all the answers

Which of the following is NOT an optimization criterion in operating system scheduling?

Max waiting time Signup and view all the answers

How does throughput relate to process scheduling?

It's the number of processes that complete execution per time unit Signup and view all the answers

Which scheduling strategy would generally result in the lowest average waiting time?

Shortest-Job-First Signup and view all the answers

In a time-sharing environment, which timing metric emphasizes the delay before the first response is produced?

Response time Signup and view all the answers

Which of the following is true regarding FCFS scheduling when processes arrive in the order P1, P2, P3?

P2 has a waiting time of 0 Signup and view all the answers

What is the primary criterion for preemptive scheduling in Shortest-Remaining-Time-First (SRTF)?

Preempt if a new process has a shorter burst length than the remaining time. Signup and view all the answers

In a non-preemptive Shortest Job First (SJF) scheduling example, what is the average waiting time for the processes P1, P2, P3, and P4?

4 Signup and view all the answers

Which scheduling method is associated with a potential problem of starvation?

Priority Scheduling Signup and view all the answers

What is the solution to the starvation problem in priority scheduling?

Implement aging to gradually increase the priority of older processes. Signup and view all the answers

In preemptive SJF scheduling, which process executes first given the following arrivals: P1 (0.0, 7), P2 (2.0, 4), P3 (4.0, 1), P4 (5.0, 4)?

P1 Signup and view all the answers

What defines the priority in Shortest Job First (SJF) scheduling?

The burst time of the process. Signup and view all the answers

What is the average waiting time calculated for processes in preemptive SJF given their finishing times?

3 Signup and view all the answers

Which statement regarding process scheduling is accurate?

SJF can be both preemptive and non-preemptive. Signup and view all the answers

What effect does the burst time have on the allocation of CPU in priority scheduling?

Shorter burst times always receive higher priority. Signup and view all the answers

What is one consequence of using preemptive scheduling for low-priority processes?

They may experience starvation if high-priority processes keep arriving. Signup and view all the answers

Study Notes

CPU Scheduling

CPU scheduling is the task of selecting a process from the ready queue and allocating the CPU to it.
Multiprogramming maximizes CPU utilization by managing multiple processes.
Process execution alternates between CPU bursts and I/O waits.

Basic Concepts

Multiprogramming increases CPU use by switching between multiple processes.
CPU-I/O bursts: Process alternates between CPU and I/O activities.
CPU burst time distribution describes the variation in CPU usage for different processes.

CPU Scheduler

Chooses and allocates the CPU to a ready process.
Decisions happen under various conditions (state transitions).
Scheduling under certain conditions (process termination or switching to waiting state) is nonpreemptive.
All other scheduling types are preemptive.

Dispatcher

The dispatcher gives the CPU to the process.
It involves switching contexts, switching to user mode, and jumping to the proper location in the user program to restart.
Dispatch latency measures the time between process switching.

Scheduling Criteria

CPU utilization wants to keep the CPU busy.
Throughput measures completed processes per time unit.
Turnaround time is the total time to complete a process.
Waiting time is the time spent in the ready queue.
Response time is the time to get the first response from request until output.

Optimization Criteria

Maximum CPU utilization
Maximum throughput
Minimum turnaround time
Minimum waiting time
Minimum response time

First-Come, First-Served (FCFS) Scheduling

Processes are scheduled in the order they arrive.
Simple to understand and implement.
Can lead to poor performance if one process takes a long time.
Example calculation included (example process arrival and burst times from the document.)
Convoy effect is a problem with one long process making many short processes wait for service

Shortest-Job-First (SJF) Scheduling

Schedules the process with the shortest next CPU burst time.
Optimal in terms of minimum average waiting time for a set of processes.
Nonpreemptive and preemptive versions.

Example of Non-Preemptive SJF

Average waiting time calculation example for this scheduling method included.

Example of Preemptive SJF

Average waiting time calculation example for this scheduling method. Results in fewer context switches.

Priority Scheduling

Each process has a priority number (lower number means higher priority).
Processes with higher priority get the CPU first.
Can lead to starvation of low-priority processes (processes might never get the CPU), thus aging can be used
SJF is a priority scheduling where priority depends on the predicted next CPU burst time.

Round Robin (RR) Scheduling

Each process gets a fixed time quantum for CPU use.
If a process does not complete in its quantum, it's moved to the back of the queue.
Good for time-sharing systems to provide quick response times for multiple processes.
Increases context switching when quantum is small and impacts performance.

Multilevel Queues

System has multiple queues based on process characteristics which are scheduled using different algorithms based on type.

Multilevel Feedback Queues

Processes move between queues based on their behavior.
Dynamically adjusts to changing process demands.

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Description

This quiz covers the fundamental concepts of CPU scheduling, including multiprogramming, process execution, and the role of the CPU scheduler and dispatcher. You'll explore how processes are managed and allocated CPU time, along with the implications of preemptive and nonpreemptive scheduling. Test your understanding of these essential topics in operating systems.