CPU Scheduling

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Questions and Answers

What is the primary goal of multiprogramming in operating systems?

To increase CPU utilization

What is the primary function of the dispatcher module?

To give control of the CPU to the process selected by the CPU scheduler

In the CPU-I/O Burst Cycle, what occurs after a CPU burst?

I/O wait

What is dispatch latency?

The time it takes for the dispatcher to stop one process and start another running Signup and view all the answers

What is the primary concern in CPU scheduling?

CPU burst distribution Signup and view all the answers

What is the primary goal of CPU utilization?

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

What is turnaround time in the context of process scheduling?

The time it takes for a process to complete its execution Signup and view all the answers

When does the CPU scheduler make scheduling decisions?

When a process is in the ready queue Signup and view all the answers

What is waiting time in the context of process scheduling?

The amount of time a process has been waiting in the ready queue Signup and view all the answers

What is the purpose of a histogram of CPU-burst times?

To analyze CPU burst distributions Signup and view all the answers

What is response time in the context of process scheduling?

The time it takes from when a request was submitted until the first response is produced Signup and view all the answers

What is the difference between preemptive and non-preemptive scheduling?

Non-preemptive scheduling allows for process suspension Signup and view all the answers

What is the primary goal of CPU scheduling algorithms?

To maximize CPU utilization Signup and view all the answers

What is the benefit of multiprocessor and multicore scheduling?

Increased CPU utilization Signup and view all the answers

What is one of the optimization criteria for scheduling algorithms?

Max throughput Signup and view all the answers

In the First-Come-First-Served (FCFS) scheduling algorithm, what is the average waiting time if the processes arrive in the order P1, P2, P3?

17 Signup and view all the answers

What is the effect observed in FCFS scheduling when a short process is behind a long process?

Convoy effect Signup and view all the answers

What is the scheduling algorithm that associates with each process the length of its next CPU burst?

SJF Signup and view all the answers

What is the advantage of the SJF scheduling algorithm?

It gives minimum average waiting time for a given set of processes Signup and view all the answers

What is the scheduling algorithm that uses time quanta to allocate the CPU?

Round Robin Scheduling Signup and view all the answers

What is the term used to describe the CPU utilization when multiple processes are being executed?

Multiprogramming Signup and view all the answers

What is the name of the Gantt chart that represents the schedule of processes in FCFS scheduling?

Gantt chart Signup and view all the answers

Study Notes

Basic Concepts

Maximum CPU utilization is obtained with multiprogramming
CPU-I/O Burst Cycle: process execution consists of a cycle of CPU execution and I/O wait
CPU burst distribution is of main concern

CPU scheduler selects a process from the ready queue and allocates a CPU core to it
Scheduling decisions may take place when a process:
- Arrives in the ready queue
- Terminates
- Requires I/O
- Completes its time slice

Scheduling Criteria

Max CPU utilization
Max throughput
Min turnaround time
Min waiting time
Min response time

First-Come, First-Served (FCFS) Scheduling

Process scheduling algorithm where processes are executed in the order they arrive
Example: P1 arrives first, then P2, then P3
Gantt chart shows the order of execution
Waiting time for each process is calculated
Average waiting time is the total waiting time divided by the number of processes

FCFS Scheduling (Cont.)

Convoy effect: short process behind long process
Consider one CPU-bound and many I/O-bound processes

Shortest-Job-First (SJF) Scheduling

Associate each process with the length of its next CPU burst
Schedule the process with the shortest time
SJF is optimal, giving minimum average waiting time for a given set of processes
Preemptive version called shortest-remaining-time-first
Difficulty in determining the length of the next CPU burst

Dispatcher

Dispatcher module gives control of the CPU to the process selected by the CPU scheduler
Switching context and switching to user mode
Dispatch latency: time it takes for the dispatcher to stop one process and start another