![• TURN AROUND TIME:
T=[finish time]-[arrival time]
• WAITING TIME:
W=T-[service time]
• RESPONSE RATIO:
R= T/(service time)](https://image.slidesharecdn.com/schedulingpolicies-151117151527-lva1-app6892/85/OPERATING-SYSTEM-Scheduling-policies-4-320.jpg)
OPERATING SYSTEM-"Scheduling policies"
- 2. TYPES OF SCHEDULER 1.LONG-TERM SCHEDULER: DETERMINE WHICH JOBS ARE ADMITTED TO THE SYSTEM FOR PROCESSING. 2.MEDIUM-TERM SCHEDULER: WHEN TO MANY PROCESSOR ARE COMPETING FOR MEMORY,DETERMINES WHICH GETS IN/OUT. 3.SHORT –TERM SCHEDULER: DETERMINES WHICH PROCESS IN MEMORY GOES NEXT.
- 3. SCHEDULING PERFORMANCE • TURN AROUND TIME: Time process present in system • WAITING TIME: Time process present and not running • RESPONSE RATIO: Factor by which processing rate reduces
- 4. • TURN AROUND TIME: T=[finish time]-[arrival time] • WAITING TIME: W=T-[service time] • RESPONSE RATIO: R= T/(service time)
- 5. Decision Mode • NON-PREEMPTIVE: A PROCESS RUNS UNTIL ITS BOLCK ARE COMPLETES (runs until no longer ready) • PREEMPTIVE: OS CAN INTERRUPT CURRENTLY RUNNING PROCESS TO START ANOTHER ONE
- 6. FIRST-COME, FIRST-SERVED • Criteria: BT-AT Where BT=burst time AT=arival time • Mode:non-preemptive • Scheduling criteria: Jobs are excuted on first cum first serve basis
- 7. • Advantage: Easy to understand and implement. • Disadvantage: Poor in performance as average wait time is high. • Example: Pno Burst time P1 24 P2 3 P3 3 Result: p1 p2 p3
- 8. SHORTEST JOB FIRST • Mode:non-preemptive • Scheduling criteria: It is assigned to the process that has smallest next cpu burst. • Disadvantage: SJF is non-preemptive like FCFS, therefore not useful in time sharing environment.
- 9. • Example: Pno BT P1 6 P2 8 P3 7 P4 3 Result: p4 p1 p3 p2 0 3 9 16 24
- 10. SHORTEST REMAINIG TIME FIRST • Mode:pre-emptive • Scheduling criteria: The process which is having shortesr remaining time is excuted first and completed. • Advantage: Short process are handled quickly • Disadvantage: Estimation of remaining t UK me is not easy.
- 11. • Example: pno AT BT 1 0 7 2 1 6 3 2 3 4 3 1 5 4 2 6 5 1 Result: p1 p1 p3 p4 p3 p3 p6 p5 p1 p2 0 1 2 3 4 5 6 7 9 14
- 12. Highest Response Ratio • Highest Response Ratio Next(HRRN) Decision mode:non-preemptive Arbitration rule: schedules job having highest response ratio and runs until completion. Priority function:p(a,r,t)= = (burst time+waiting time) _________________________ burst time
- 13. *Advantages: – It is better than SRTF & SJF *Disadvantages: – Caculation of response ratio *Example: Pno AT BT 1 0 3 2 2 6 3 4 4 4 6 5 5 8 2 Result: p1 p2 p3 p5 p4 0 3 9 13 15 20
- 14. ROUND ROBIN • Criteria: AT+TQ where AT=arival time TQ=time quantum • Mode: pre-emptive • Scheduling criteria: It schedules job as per AT (takes from front of queue) & executes till TQ is completed (then puts back to request queue) or time is over.
- 15. Thank you