1 / 12

Understanding CPU Scheduling Algorithms: FCFS, SJF, RR, and Priority Techniques

This resource provides an overview of key CPU scheduling algorithms used in operating systems, including First-Come, First-Served (FCFS), Shortest-Job-First (SJF), Round-Robin (RR), and Priority Scheduling. It discusses the differences between preemptive and non-preemptive scheduling, highlighting pros and cons, as well as how to measure CPU utilization, throughput, turnaround time, and waiting time. Additionally, it explores multilevel queues and feedback queues for efficient process management. Perfect for students and professionals seeking to enhance their understanding of OS scheduling mechanisms.

inga
Télécharger la présentation

Understanding CPU Scheduling Algorithms: FCFS, SJF, RR, and Priority Techniques

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Rensselaer Polytechnic Institute CSCI-4210 – Operating Systems David Goldschmidt, Ph.D. Operating Systems{week 05b}

  2. Short-term (CPU) scheduling the dispatcher operates here

  3. CPU scheduling algorithms (i) • CPU scheduling requires an algorithm todetermine which process to dispatch next • Scheduling algorithms include: • First-Come, First-Served (FCFS) • Shortest-Job-First (SJF) • Round-Robin (RR) • Priority • Multilevel Queue (MQ)

  4. process CPU scheduling algorithms (ii) • Preemptive scheduling preempts a running process before itstime slice expires • Or it preempts a processbecause its time slice has expired • Non-preemptive scheduling gives a process exclusive uninterrupted access to the CPU for the entirety of its execution process process process

  5. CPU scheduling algorithms (iii) • Compare scheduling algorithms by measuring • CPU utilization – keep CPU as busy as possible • Throughput – maximize the number of processes that complete their execution per unit time • Turnaround time – minimize the elapsed time to fully execute a particular process • Waiting time – minimize the elapsed time a process waits in the ready queue

  6. P3 P1 P2 P3 P1 P3 P1 0 2 4 6 8 10 12 13 Round-Robin (RR) • RR is a preemptive algorithmthat gives all ready processesa fair time slice of CPU time • Using a time slice of 2 ms.... time

  7. Priority Scheduling (i) • Associate a priority number with each process • The dispatcher selects the processwith the highest priority • For multiple ready processes withidentical priority numbers, use FCFS (or ...) • Key problem is starvation • Overcome starvation by aging, increasingthe priority of a process as it ages

  8. process Priority Scheduling (ii) • Is priority scheduling preemptiveor non-preemptive? • Non-preemptive priority scheduling places higher-priority processes at the head of the queue • Preemptive priority scheduling requires a running process to be interrupted and preempted upon the arrival of a higher-priority process (use this one for Project #1)

  9. Multiclass systems • Operating systems that support priority schemes are often called multiclass systems use a separate schedulingalgorithm for each queue

  10. Multilevel Queue (MQ) • Assign processes to multiple queues,each with its own scheduling algorithm

  11. Multilevel Feedback Queue (MFQ) • Dynamically assign processes to multiple queues based on actual CPU burst times • i.e. feedback quantum is synonymouswith time slice

  12. Practice! • Apply the FCFS, SJF, RR, and Preemptive Priority scheduling algorithms to this table: • For RR, use a time slice of 10 ms • Calculate the wait and turnaround times ofeach process, as well as overall averages lower number indicates a higher priority recalculate using context switch time tcs = 20 μs

More Related