CPU Scheduling - scheduling criteria and algorithms, thread scheduling, multiprocessor and real-time scheduling - One Line Questions

1. What is 'hybrid thread model' scheduling? — A model that combines user-level threads with kernel-level threads, allowing for both flexibility and concurrency.
2. What is 'hard affinity' in multiprocessor scheduling? — A strict policy that a thread must run on a specific processor.
3. What is a 'thread' in the context of operating systems? — A lightweight unit of execution within a process
4. What is 'soft affinity' in multiprocessor scheduling? — An attempt to keep a thread on the same processor, but not a strict requirement.
5. What is 'asymmetric multiprocessing' (AMP) system? — A system where one CPU (master) controls the system and schedules tasks for other CPUs (slaves).
6. What is a 'soft real-time system'? — A system where missing a deadline is undesirable but the system can still function.
7. What is a 'hard real-time system'? — A system where missing a deadline is catastrophic.
8. What is a 'symmetric multiprocessing' (SMP) system? — A system where all CPUs are treated equally and can perform any task.
9. What is an 'aperiodic task' in real-time scheduling? — A task that arrives sporadically and does not have a fixed period.
10. What is a 'periodic task' in real-time scheduling? — A task that executes at regular, fixed intervals.
11. In Rate Monotonic Scheduling (RMS), how are priorities assigned? — Based on the shortest period (highest frequency).
12. In First-Come, First-Served (FCFS) scheduling, how is the CPU allocated? — In the order processes arrive in the ready queue
13. In Multilevel Queue Scheduling, how is scheduling done between queues? — Scheduling between queues is typically done using fixed priority preemptive scheduling
14. What is 'load balancing' in the context of multiprocessor scheduling? — Distributing processes or threads evenly across all available processors to maximize utilization.
15. Which scheduling algorithm guarantees the minimum average waiting time? — SJF (Shortest-Job-First)
16. Preemptive Shortest-Job-First is also known as: — Shortest-Remaining-Time-First (SRTF)
17. Which real-time scheduling algorithm is optimal if the system is fully preemptible and all tasks are periodic? — Rate Monotonic Scheduling (RMS)
18. Which scheduling algorithm is generally preferred for multiprocessor systems to achieve good performance and fairness? — Global Multiprocessor Scheduling
19. Which technique can be used to mitigate the starvation problem in priority scheduling? — Aging - gradually increasing the priority of processes that have been waiting for a long time
20. What is a potential problem with priority scheduling? — It can cause starvation, where low-priority processes may never get to execute
21. What is a significant disadvantage of the FCFS scheduling algorithm? — It can lead to the convoy effect, where short processes get stuck behind long ones
22. What is the main challenge in implementing SJF scheduling in a real-time system? — It is difficult to determine the exact burst time of a process in advance
23. What is a major disadvantage of kernel-level thread scheduling? — Thread switching is slower because it requires a mode switch to the kernel.
24. What is the primary advantage of using Earliest Deadline First (EDF) scheduling? — It can theoretically schedule any set of tasks if they are schedulable.
25. What is a major disadvantage of user-level thread scheduling? — If one thread blocks on a system call, all threads within the process block.
26. What is a major advantage of user-level thread scheduling? — Faster thread switching as it does not involve kernel mode transition.
27. Which of the following is a primary goal of CPU scheduling? — Maximize CPU utilization and throughput
28. What is a primary characteristic of real-time scheduling? — Meeting deadlines and predictability
29. What is the difference between Multilevel Queue Scheduling and Multilevel Feedback Queue Scheduling? — Multilevel Feedback Queue allows processes to move between queues.
30. Shortest-Job-First (SJF) scheduling is an example of which type of scheduling? — Non-preemptive
31. Multilevel Queue Scheduling divides the ready queue into several separate queues. What is a common basis for this division? — Process priority or type (e.g., foreground, background)
32. What is the primary characteristic of Round Robin (RR) scheduling? — Processes are given a fixed time slice (time quantum) of CPU time
33. Which scheduling algorithm is known for its dynamic priority assignment based on deadlines? — Earliest Deadline First (EDF)
34. What is 'kernel-level thread scheduling'? — Scheduling of threads managed directly by the operating system kernel.
35. What is 'user-level thread scheduling'? — Scheduling of threads managed by a thread library within the user process.
36. In SRTF, if a new process arrives with a CPU burst length shorter than the remaining time of the currently executing process, what happens? — The CPU is preempted and allocated to the new process
37. Which factor significantly impacts the performance of Round Robin scheduling? — The length of the time quantum
38. In many operating systems, what is the relationship between a process and its threads regarding scheduling? — The operating system schedules threads directly, and threads from different processes can be interleaved.
39. What happens if a process's CPU burst time is longer than the time quantum in Round Robin scheduling? — The process is preempted and moved to the end of the ready queue
40. In multiprocessor scheduling, what is 'affinity'? — The tendency for a thread to run on a particular processor.
41. What does 'turnaround time' refer to in CPU scheduling? — The total time from submission of a process to its completion
42. What is a major advantage of kernel-level thread scheduling? — If one thread blocks, other threads of the same process can be scheduled by the kernel.
43. How does thread scheduling differ from process scheduling? — Threads share the process's resources, making scheduling less complex.
44. In real-time systems, what is the 'schedulability analysis' used for? — To ensure that all tasks will meet their deadlines under a given scheduling algorithm.
45. In Multilevel Feedback Queue Scheduling, what is the purpose of allowing processes to move between queues? — To prevent starvation and adapt to the process's behavior
46. What is the primary responsibility of the operating system in thread scheduling? — To allocate CPU time to threads
47. Priority scheduling assigns a priority level to each process. How is the CPU allocated? — To the process with the highest priority
48. Which scheduling criterion aims to keep the CPU as busy as possible? — CPU utilization
All One Line Questions
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