Chapter 5: CPU Scheduling

Flashcards based on key concepts from Chapter 5 on CPU Scheduling.

What does the CPU scheduler do?

The CPU scheduler selects one process among all processes in the ready state and allocates the CPU to it.

What is a ready queue?

A list where records in the ready queue are Process Control Blocks (PCBs) of the processes that are in the ready state, but it is not necessarily a FIFO queue.

What is a CPU-I/O Burst Cycle?

It refers to the cycle of CPU execution and I/O wait during process execution.

What are the conditions that may trigger CPU scheduling decisions?

1. Switches from running to waiting state (I/O request). 2. Switches from running to ready state (interrupt). 3. Switches from waiting to ready (completion of I/O). 4. Terminates.

What is the difference between preemptive and nonpreemptive scheduling?

Preemptive scheduling allows the CPU to be taken away from a process during its execution, while nonpreemptive scheduling means the process retains the CPU until it voluntarily releases it.

What does the dispatcher module do?

The dispatcher module gives control of the CPU to the selected process by switching context, switching to user mode, and jumping to the proper location in the user program.

Name at least two criteria for scheduling. What do they measure?

1. CPU utilization – measures how busy the CPU is. 2. Throughput – measures the number of processes that complete execution per time unit.

What is the main goal of scheduling algorithms optimization criteria?

To minimize the average waiting time of all processes.

Explain the First-Come, First-Served (FCFS) scheduling algorithm.

Processes are scheduled in the order they arrive, with each process waiting for the previous one to finish.

What does the Shortest-Job-First (SJF) scheduling algorithm do?

It schedules the process with the shortest next CPU burst time, aiming for minimum average waiting time.

What is Round Robin (RR) scheduling and how does it work?

Each process gets a small unit of CPU time (time quantum). When time expires, the process is preempted and added to the end of the ready queue.

What is the main advantage of multilevel feedback queues?

They allow processes to move between different queues, with aging applied to manage priority.

Describe a real-time CPU scheduling system. What challenges does it face?

It is designed to meet strict timing requirements. Soft real-time systems provide high priority to critical tasks, while hard real-time systems must ensure tasks are serviced by their deadlines.

What is Little’s Formula and its components?

Little's Formula states n = λ x W, where n is the average queue length, λ is the average arrival rate, and W is the average waiting time in the queue.

How do simulations improve the evaluation of CPU schedulers?

Simulations provide more accurate models of the computer system, allowing for performance statistics to be gathered based on various scheduling algorithms.