1. 3.1 : Resource Management Part2 :Processor Management

2. Learning Outcomes 3.1.1 Understand Processor Management 3.1.2 Various type of scheduling processes 3.1.3 Scheduling Algorithms – First in first out (FIFO) – Shortest Job First (Nonpreemptive SJF) – Shortest Remaining Time (Preemptive SJF) – Round Robin Scheduling – Priority

3. Processor Management To know how Processor Manager allocates a single CPU to execute the jobs / processes from those user. Task of Processor Manager : Decide i.How to allocate the CPU ii.Monitor whether it’s executing or waiting a process. iii.Control job entry to ensure balanced use of resources

4. Process Process is a program in execution When process execute it changes state State represent process’s current activity Each process may be in one of the following state, which are : – New : the process is being created – Running : instruction are being executed – Waiting : the process is waiting for some event to occur (reception of signal) – Ready : the process is waiting to be assigned to a processor – Terminated : the process has finished execution

5. Process Waiting queue is place for not executing process. Ready queue is contains all the processes that are ready to execute and waiting for the CPU. Each process is represent by PCB (Process Control Block)

6. PCB (Process Control Block) PCB contains many pieces of information with specific process which are; – Process state : new, running, waiting, ready and terminated – Program counter : the counter indicate the address of the next instruction to be executed – CPU Register: include accumulator, index register stack pointer and so on. – CPU Scheduling algorithm : includes a process priority, or others CPU scheduling algorithm – Memory – management information : may include such information as the value of the limit and base register, the page table or segment table, depend on which memory scheme used by operating system. PCB can linked together to a ready queue

7. Scheduling Concept The objective of Multiprogramming is to have some process running at all times, - to maximize CPU utilization Objective of Time-Sharing is to switch the CPU among processes – so frequently that user can interact with each program while it is running. A uniprocessor/ single – user system can have only one running process. If more processes exist, the rest must wait until the CPU is free and can be rescheduled.

8. Process Scheduling Therefore process scheduling is need for schedule processes on your system Why to schedule ? To decide which process to run first if there have more than one process is run able. Scheduler is part of O/S which make this decision.

9. Schematic of scheduling  Figure above is shows movement of requests in the system  All requests waiting to be executed are kept in a list of pending requests.  Whenever scheduling is to be performed, the scheduler examines the pending request and select one for executing. Scheduler CPU Scheduled request Arriving requests Completed request Preempted request Pending requests Data flow Control Flow  This request is handed over to the CPU.  A request leaves the CPU when it completes or when it is preempted by the scheduler.  In which case, it is put back into the list of pending request  In either situation, scheduler performs scheduling to select next request to be executed.

10. Cont.. Preemptive – Interrupts the processing of a job and transfer the CPU to another job. – Strategy of allowing process that are logically run able to be suspended. – It is widely used in time-sharing environments Nonpreemtive – Always processes a scheduled request to completion – Since only one request is under processing by the CPU at any time, it is not necessary to maintain the distinction between long, medium and short – term scheduling – Example of scheduling are FCFS and SJF scheduling

11. Type of scheduling processes : Long – term Scheduling – Also known as job scheduling – Is the selection of processes to be allowed to compete for the CPU. – Normally Long – Term Scheduling is heavily influenced resource – allocation consideration, especially memory management.

12. Type of scheduling processes : Short– term Scheduling – Also known as CPU Scheduling – Is the selection of one process from ready queue(all the processes that are ready to execute and waiting for the CPU)

13. Scheduling Creteria 1.CPU utilization (Penggunaan CPU) - keep the CPU as busy as possible 2.Throughput(Daya Pemprosesan) – number of processes that complete their execution per time unit 3.Turnaround time (Masa pusingan)– amount of time to execute a particular process 4.Waiting time( Masa menunggu) – amount of time a process has been waiting in the ready queue 5.Response time(Masa tindakbalas) – amount of time it takes from when a request was submitted until the first response is produced, not output (for time-sharing environment)

14. Optimization Criteria Max; – CPU utilization – throughput Min; – turnaround time – waiting time – response time

15. Scheduling Algorithm : First Come First Serve Is nonpreemptive scheduling algorithm. Handles job according to their arrival time. The early arrive the, the sooner they’re served. It’s very simple algorithm to implement because it uses FIFO queue. This algorithm is fine for most batch system, but it unacceptable for interactive systems because interactive users expect quick response time

16. Example : FCFS ProcessBurst Time (ms) P 1 24 P 2 3 P 3 3 The Gantt Chart for the schedule is: Waiting time for P 1 = 0ms; P 2 = 24ms; P 3 = 27ms Waiting time for P 1 = 0ms; P 2 = 24ms; P 3 = 27ms Average waiting time: (0 + 24 + 27)/3 = 17ms Average waiting time: (0 + 24 + 27)/3 = 17ms P1P1P1P1 P2P2P2P2 P3P3P3P3 2427300

17. Exercise 1: FCFS What will happened if the processes arrive in the order  P 2, P 3, P 1 What will happened if the processes arrive in the order  P 2, P 3, P 1 i.Draw a gantt chart ii.Calculate average waiting time

18. Scheduling Algorithm : Shortest Job First (SJF) Handles jobs based on the length of their CPU cycle time/ burst time. When CPU available, it is assigned to the process that has smallest next CPU burst. If two processes have the same length next CPU burst, FCFS scheduling is used to break the tie. The SJF scheduling algorithm is optimal  that is gives the minimum average waiting time for a given set of processes.

19. Scheduling Algorithm : Shortest Job First (SJF) Two schemes: Two schemes: – nonpreemptive – once CPU given to the process it cannot be preempted until completes its CPU burst. – preemptive – if a new process arrives with CPU burst length less than remaining time of current executing process, preempt. This scheme is know as the Shortest-Remaining-Time-First (SRTF).

20. Scheduling Algorithm : Shortest Job First (SJF) Nonpreemptive P4 9 P3P1P2 1 1624 0 ii) Waiting time; P1= 3; P2=16; P3=9; P4=0 iii) Average waiting time; = ( 3 + 16 + 9 + 0 )/ 4 = 7 ms ProcessBurst TimeArrival Time P160 P280 P370 P430

21. Scheduling Algorithm : Shortest Job First (SJF) Nonpreemptive ProcessBurst TimeArrival Time P170 P242 P314 P445 P1P1P1P1 P3P3P3P3 P2P2P2P2 7160 P4P4P4P4 812 iii) AWT = (0 + 6 + 3 + 7)/4  4 ii) Waiting Time 1.P1 = 0 2.P2 = 8 – 2 = 6 3.P3 = 7 – 4 = 3 4.P4 = 12 – 5 = 7

22. Exercise SJF Nonepreemptive Open your labwork book, page 11(Activity 2)

23. Scheduling Algorithm : Shortest Job First (SJF) Preemptive / SRTF Rules : Current process preempted if a new process with CPU burst time less than remaining burst time for current executing process.

24. Example 1: SRTF ProcessBurst TimeArrival Time P1100 P222 P1P1P1P1 4 2 0 P1P1P1P1 12 P2P2P2P2 ii) Waiting Time P1 = 0 + (4-2) = 2 P2 = 2-2 = 0 ii) AWT P1+P2 = 1ms 2

25. Exercise 1: SRTF Open your labwork book, page 11(Activity 2)

26. Exercise 2 : SRTF i)Draw a gantt chart ii)Calculate are waiting time for each process iii)Calculate average waiting time ProcessBurst TimeArrival Time P1240 P231 P332 P413

27. Scheduling Algorithm: Round Robin Scheduling /RR Is a preemptive process scheduling algorithm Each process gets a small unit of CPU time (time quantum/time slice), usually 10-100 milliseconds. Each process gets a small unit of CPU time (time quantum/time slice), usually 10-100 milliseconds. Time quantum = time interval Time quantum = time interval After this time has elapsed, the process is preempted and added to the end of the ready queue. After this time has elapsed, the process is preempted and added to the end of the ready queue.

28. Scheduling Algorithm: RR Scheduling ProcessBurst Time Time Quantum = 4ms P124 P23 P33 P1 0 10718 P1P3P2P1P1P1P1 14 4 262230 ii) Waiting time 1. P1 = (0 + (10-4)) = 6 ms 2. P2 = 4 ms 3. P3 = 7 ms iii) Average waiting time = ( 6 + 4 + 7 )/ 3 = 5.66 ms

29. Exercise 1: RR Scheduling Open your labwork book, page 14 (Activity 1)

30. Scheduling Algorithm: Priority Scheduling A priority number (integer) is associated with each process A priority number (integer) is associated with each process The CPU is allocated to the process with the highest priority (smallest integer = highest priority). The CPU is allocated to the process with the highest priority (smallest integer = highest priority). – Preemptive – nonpreemptive SJF is a priority scheduling where priority is the predicted next CPU burst time. SJF is a priority scheduling where priority is the predicted next CPU burst time. Problem  Starvation ( low priority processes may never execute) Problem  Starvation ( low priority processes may never execute) Solution  Aging ( as time progresses increase the priority of the process) Solution  Aging ( as time progresses increase the priority of the process)

31. Example 1: Priority Scheduling ProcessBurst TimePriority P1103 P211 P324 P415 P552 P2 6 P3P1P5P4 1 181619 0 ii) Waiting time 1. P1 = 6 ms 2. P2 = 0 ms 3. P3 = 16 ms 4. P4 = 18 ms 5. P5 = 1 ms iii) Average waiting time = ( 6 + 0 + 16 + 18 + 1 )/ 5 = 8.2 ms

32. Exercise 1: Priority Scheduling Open your labwork book, page 15 (Activity 2)