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Questions and Answers
What is the primary purpose of CPU scheduling in multiprogrammed operating systems?
What is the primary purpose of CPU scheduling in multiprogrammed operating systems?
- To maximize CPU utilization (correct)
- To reduce memory usage
- To increase power consumption
- To manage I/O devices
Which of the following best describes a CPU–I/O burst cycle?
Which of the following best describes a CPU–I/O burst cycle?
- An error state of the CPU when waiting for I/O
- A continuous process execution without interruptions
- A repetitive pattern of computing followed by input/output operations (correct)
- A method of enhancing CPU speed beyond limits
What triggers CPU scheduling decisions within an operating system?
What triggers CPU scheduling decisions within an operating system?
- Switching between CPU and memory states
- Switching from running to waiting state (correct)
- Switching between user and kernel modes
- Switching from idle to active state
What is primarily evaluated when selecting a CPU scheduling algorithm?
What is primarily evaluated when selecting a CPU scheduling algorithm?
Which of the following is NOT a state change that leads to CPU scheduling decisions?
Which of the following is NOT a state change that leads to CPU scheduling decisions?
Which of the following scheduling types is nonpreemptive?
Which of the following scheduling types is nonpreemptive?
What does the dispatcher module NOT do?
What does the dispatcher module NOT do?
Which scheduling criterion focuses on keeping the CPU as busy as possible?
Which scheduling criterion focuses on keeping the CPU as busy as possible?
What is one of the drawbacks of First-Come, First-Served (FCFS) scheduling?
What is one of the drawbacks of First-Come, First-Served (FCFS) scheduling?
In Shortest-Job-First (SJF) scheduling, what is a major challenge?
In Shortest-Job-First (SJF) scheduling, what is a major challenge?
What is the average waiting time when processes P1, P2, and P3 arrive in that order with burst times 24, 3, and 3, respectively?
What is the average waiting time when processes P1, P2, and P3 arrive in that order with burst times 24, 3, and 3, respectively?
Which of the following is NOT a goal of scheduling algorithm optimization criteria?
Which of the following is NOT a goal of scheduling algorithm optimization criteria?
What average waiting time does the SJF scheduling produce with the processes P1, P2, P3, and P4 having arrival times 0.0, 2.0, 4.0, and 5.0 with burst times 6, 8, 7, and 3 respectively?
What average waiting time does the SJF scheduling produce with the processes P1, P2, P3, and P4 having arrival times 0.0, 2.0, 4.0, and 5.0 with burst times 6, 8, 7, and 3 respectively?
What is the effect called when short processes get delayed by long processes in FCFS scheduling?
What is the effect called when short processes get delayed by long processes in FCFS scheduling?
Which of the following best describes the role of the dispatcher in process scheduling?
Which of the following best describes the role of the dispatcher in process scheduling?
What effect does setting alpha ($\alpha$) to 0 have on the prediction of the next CPU burst?
What effect does setting alpha ($\alpha$) to 0 have on the prediction of the next CPU burst?
In priority scheduling, what happens to a low priority process over time?
In priority scheduling, what happens to a low priority process over time?
What does SJF stand for in the context of CPU scheduling?
What does SJF stand for in the context of CPU scheduling?
What is the main characteristic of preemptive scheduling?
What is the main characteristic of preemptive scheduling?
Given the following processes: P1 with priority 3, P2 with priority 1, P3 with priority 4, P4 with priority 5, P5 with priority 2, which process gets executed first?
Given the following processes: P1 with priority 3, P2 with priority 1, P3 with priority 4, P4 with priority 5, P5 with priority 2, which process gets executed first?
How is the average waiting time calculated in the example of preemptive SJF?
How is the average waiting time calculated in the example of preemptive SJF?
What is the typical time quantum range for Round Robin scheduling?
What is the typical time quantum range for Round Robin scheduling?
What is the potential problem associated with priority scheduling?
What is the potential problem associated with priority scheduling?
What happens when $\alpha$ is set to 1 for predicting the next CPU burst?
What happens when $\alpha$ is set to 1 for predicting the next CPU burst?
What happens to a process after its time quantum elapses in a Round Robin scheduling?
What happens to a process after its time quantum elapses in a Round Robin scheduling?
In a Round Robin schedule, if there are n processes and the time quantum is q, what is the maximum time a process can wait before it executes again?
In a Round Robin schedule, if there are n processes and the time quantum is q, what is the maximum time a process can wait before it executes again?
What is a potential downside of having a small time quantum in Round Robin scheduling?
What is a potential downside of having a small time quantum in Round Robin scheduling?
What is the typical range for time quantum in a Round Robin scheduling algorithm?
What is the typical range for time quantum in a Round Robin scheduling algorithm?
In a Multilevel Queue scheduling system, how is the ready queue organized?
In a Multilevel Queue scheduling system, how is the ready queue organized?
Which scheduling algorithms are typically associated with the foreground and background queues in a Multilevel Queue system?
Which scheduling algorithms are typically associated with the foreground and background queues in a Multilevel Queue system?
What is meant by context switch time in the context of Round Robin scheduling?
What is meant by context switch time in the context of Round Robin scheduling?
For effective operation of Round Robin scheduling, what should the burst times of CPU bursts be in relation to the time quantum?
For effective operation of Round Robin scheduling, what should the burst times of CPU bursts be in relation to the time quantum?
What is the time quantum for queue Q0 in a multilevel feedback queue?
What is the time quantum for queue Q0 in a multilevel feedback queue?
In a multilevel feedback queue, what happens to a job that does not complete in Q0 after 8 milliseconds?
In a multilevel feedback queue, what happens to a job that does not complete in Q0 after 8 milliseconds?
Which scheduling algorithm is typically used in the background queue of a multilevel queue scheduling system?
Which scheduling algorithm is typically used in the background queue of a multilevel queue scheduling system?
What types of threads can be scheduled in a many-to-many threading model?
What types of threads can be scheduled in a many-to-many threading model?
What does the PTHREAD_SCOPE_PROCESS setting specify during thread creation?
What does the PTHREAD_SCOPE_PROCESS setting specify during thread creation?
In symmetric multiprocessing (SMP), which statement is true regarding how processes are scheduled?
In symmetric multiprocessing (SMP), which statement is true regarding how processes are scheduled?
What is a characteristic of processor affinity?
What is a characteristic of processor affinity?
Which method in load balancing pushes tasks from an overloaded CPU?
Which method in load balancing pushes tasks from an overloaded CPU?
Which statement is true regarding multithreaded multicore systems?
Which statement is true regarding multithreaded multicore systems?
When upgrading a process in a multilevel feedback queue system, what factor can be implemented?
When upgrading a process in a multilevel feedback queue system, what factor can be implemented?
What does aging in a multilevel feedback queue help manage?
What does aging in a multilevel feedback queue help manage?
What library function is used to set the scheduling scope in Pthread?
What library function is used to set the scheduling scope in Pthread?
In which scenario would many-to-one thread models be most applicable?
In which scenario would many-to-one thread models be most applicable?
Study Notes
Basic Concepts
- CPU scheduling is essential for multiprogrammed operating systems to manage process execution efficiently.
- Processes alternate between CPU execution and I/O wait, forming a CPU-I/O burst cycle.
- It’s crucial to analyze the distribution of CPU burst times for effective scheduling.
CPU Scheduler
- Short-term scheduler allocates CPU to processes in the ready queue based on different criteria.
- Scheduling decisions occur during state transitions: running to waiting, running to ready, waiting to ready, or when a process terminates.
- Nonpreemptive scheduling occurs when processes terminate or switch from running to waiting, while preemptive scheduling occurs otherwise.
Dispatcher
- The dispatcher transfers CPU control to the selected process, involving context switching and user mode transitions.
- Dispatch latency refers to the time taken for the dispatcher to stop one process and start another.
Scheduling Criteria
- CPU Utilization: Aims to keep the CPU as occupied as possible.
- Throughput: Measures the number of processes completed in a time unit.
- Turnaround Time: Total time taken to execute a process.
- Waiting Time: Duration a process remains in the ready queue.
- Response Time: Time from request submission to the first response production.
Scheduling Algorithm Optimization Criteria
- Maximize CPU utilization and throughput, while minimizing turnaround, waiting, and response times.
FCFS Scheduling
- Processes are served in the order of their arrival, leading to potentially high average waiting times due to the convoy effect with CPU-bound processes.
Shortest-Job-First (SJF) Scheduling
- SJF schedules processes based on the length of their next CPU burst, minimizing average waiting time when the next burst is known or estimated.
- Preemptive SJF is termed shortest-remaining-time-first, allowing ongoing processes to be preempted by shorter ones.
Priority Scheduling
- Processes are assigned priority levels, allowing higher priority (smaller integer) processes to preempt lower priority processes.
- A potential problem of starvation for low-priority processes can be mitigated through aging, which increases the priority of long-waiting processes.
Round Robin (RR)
- Each process receives a fixed time quantum (q), cycling through the ready queue for better responsiveness but potentially higher turnaround times.
- Ideal quantum size should be larger than the context switch time to avoid excessive overhead.
Multilevel Queue Scheduling
- The ready queue is divided into multiple queues, each with its own scheduling algorithm, such as RR for foreground and FCFS for background processes.
- Scheduling types can include fixed priority allocation or time-slice distribution between queues.
Multilevel Feedback Queue
- Processes can transition between queues based on their execution behavior, incorporating aging to adjust process priorities dynamically.
- Defined through parameters such as number of queues, scheduling algorithms, and promotion/demotion criteria.
Thread Scheduling
- Distinction between user-level and kernel-level threads, utilizing many-to-one or many-to-many models.
- Thread scheduling can be based on process-contention scope (PCS) or system-contention scope (SCS).
Multiple-Processor Scheduling
- Requires more complex scheduling as processes may run on multiple homogeneous processors.
- In asymmetric multiprocessing, one processor manages system data, while symmetric multiprocessing (SMP) allows all processors to schedule independently.
- Processor affinity, either soft or hard, refers to a process's tendency to run on the same processor.
Load Balancing in Multiprocessors
- Load balancing is crucial in SMP environments for efficiency, utilizing push migration to redistribute tasks from overloaded CPUs, or pull migration where idle CPUs fetch tasks from busy ones.
Multicore Processors
- Trend towards integrating multiple processor cores in a single chip for improved performance and reduced power consumption.
- Multithreading capability per core is on the rise to enhance throughput during memory operations.
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Description
This quiz covers Chapter 6 on CPU Scheduling from Operating Systems. It includes topics such as scheduling criteria, algorithms, thread scheduling, and real-time CPU scheduling. Test your understanding of various CPU-scheduling concepts and their evaluation criteria.
