CPU Scheduling

Question

Pno	Arrival Time	1st IO	Burst time	2nd IO
P1	0	4	14	2
P2	0	8	28	4
P3	0	12	42	6

Using SRTF:-

Completion time :- P1 -  18, P2 - 46, P3 - 88

Turnaround Time:- According to the definition of Galvin it is 

Turnaround time is the sum of the periods spent waiting to get into the memory, waiting in the ready queue, executing on the CPU, and Doing I/O. Page no = 187, 8th Edition

P1 - 20, P2 - 50, P3 - 94.

Waiting time :- According to the definition of Galvin it is

Waiting time is the sum of periods spent waiting in the ready queue. Page no = 187, 8th Edition

WT = TAT - Burst time - IO time

P1 = 20 - 14 - 4 - 2 = 0.

P2 = 50 - 28 - 8 - 4 = 10

P3 = 94 - 42 - 12 - 6 = 34.

Someone Verify these calculations.

Comments

So, completion time is the time at which process finally completes, and not the process last time use the CPU.

It should include Last I/O (if any).

ryt?

And waiting time calculation is correct ryt? 

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@sumit goyal1

I think completion time for P1=16

because arrival time for P1=0 and it is not told that time of IO, CPU should remain idle

rt?

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mam,if it is not mention that during i/o cpu remains idle or not then what will be possible scenerio here ,no any process can execute because only p1 have small BT.without doing it's own I/O it can't be executed.

Answer 1

i think completion time of a process is defined as completion of all the service time of the process.then it includes before i/o,burst time,after i/o..so p1 may complete at 20ms and p2 may complete at 50ms and p3 may complete at 94 ms....so the tat for all process is equal to its completion time...wait time for p1 is (20-4-14-2)=0 ms,for p2 is (50-8-28-4)=10 ms,for p3 is (94-12-42-6)=34 ms

Answer 2

CPU IDLE

P1

P2

P3

CPU IDLE

0..................................4..............18.............46...............88......................94

i/o for P0 ,P1,P2 FOR 4 UNIT OF TIME