Round Robin Scheduling

Question

Consider a System using Round Robin scheduling with 10 Processes all arriving at the time 0. Each Process is associated with 20 identical Request. Each Process request consumes 20 ms of CPU time after which it spends 10 ms of time on I/O,thereafter intiates subsequent Request. Assuming scheduling Overhead of 2 ms and Time Quantum of 20 ms, Calculate

i. Response time of the 1^st Request of the 1^st Process.

ii. Response time of the 1^st Request of the last Process.

iii. Response time of the subsequent request of any process.

Comments

(1) response time of first process =10 unit

(2) response time of the last process=108 unit

correct me if i am wrong.

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@ BASANT KUMAR How do you get 1^st Request of the 1^st Process 10 unit? I think it will be 2. 

Answer 1

response time of first request=2ms.

response time of 1st request of the last process=9*(20+2)+2=200ms.

Comments

are we assuming that the context switch happens in the begginning

Answer 2

ANS:

Answer 3

response time of first request of first process=2+20=22ms

Response time of first request of last process =(2+20)*10=220ms

Response time of subsequent request of any process=10+210=220ms

 

Comments

Can you please explain that why should we not consider 10ms of I/O in response time. For instance, here response time of first request of P1 should actually be 32ms, because only after that will we get the output of first request of first process.

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source: stack overflow

Response time - The time taken in a program from the issuance of a command to the commence of a response to that command.(i.e., the time-interval between submission of a request, and the first response to that request, not the output .)  

here in the question request itself takes 20 ms

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why the response time of the first process cannot be zero, since it gets schedued immediately, it does not have to wait