Mohammad Ali Khan & Sadia Afrin Dept. of Computer Science & Engineering Faculty of Engineering University of Development Alternative (UODA)
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Mohammad Ali Khan&
Sadia Afrin
Dept. of Computer Science & EngineeringFaculty of Engineering
University of Development Alternative (UODA)
Maximum CPU utilization obtained with multiprogramming.
Scheduling :- A method of assigning CPU to a process.
Scheduling is the basis of multi-programmed OS.
BASIC CONCEPTS
CPU – I/O BURST CYCLE
1. When A process switches from the running state to waiting state ( due to an I/O request ).
2. When A process switches from the running state to ready state ( due to end of time slice ).
3. When A process switches from the waiting state to ready state ( at completion of I/O ).
4. When A process terminates.
CPU SCHEDULER
CPU Utilization – Keep the CPU as busy as possible.
Throughput – Number of processes that complete their execution per time unit.
Turnaround Time – Amount of time to execute A particular process.
Waiting Time – Amount of time A process has been waiting in the ready queue.
Response Time – Amount of time it takes from when A request was submitted until the first response is produced, not output (for time-sharing environment).
SCHEDULING CRITERIA
TYPES OF CPU SCHEDULING ALGORITHM
First-Come-First-Served Scheduling Round-Robin Scheduling
Priority Scheduling Shortest-Job-First Scheduling
PRIORITY SCHEDULING
► A priority number (integer) is associated with each
process.
► Smallest integer ≡ Highest priority.
► The CPU is allocated to the process with highest priority.
► Can be Preemptive or Non-preemptive.
► Equal priority processes are scheduled on FCFS.
Process Priority Burst time (ms) P1 3 10 P2 1 1 P3 3 2 P4 4 1 P5 2 5
P2 P5 P1 P3 P40 1 6 1
618 1
9Chart 1
Average waiting time = (6+0+16+18+1) / 5 = 41/5 =8.2 ms
PRIORITY SCHEDULING
PRIORITY SCHEDULING
DISADVANTAGES ►If system eventually crashes, all low priority processes get lost.► Indefinite blocking or Starvation.
ADVANTAGES ► Aging :- As time increases , increase in the priority of a process.► Simplicity.► Suitable for applications with varying time and resource requirement.
Related Documents
