Observe a single processor system that has two supporting running processes, A a

Question

Observe a single processor system that has two supporting running processes, A and B, with the following sequential execution patterns:
             A: [CPU 8 ms; IO 1 ms; CPU 8 ms; IO 1 ms;    CPU 8 ms]
             B: [CPU 2 ms; IO 1 ms; CPU 2 ms; IO 1 ms; CPU 2 ms]

             Assume that IO operations do not interfere with each other and are blocking, and that
             scheduling and context switch times are negligible.
             What is the total elapsed time for the two processes to run to completion?   

Explanation / Answer

The total run time depends on the type of scheduling.

If B starts only after A has finished its entire running:

Time taken for A = 8+1+8+1+8 = 26ms

Time taken for B = 2+1+2+1+2 = 8ms

Total time taken = A+B = 26+8 = 34ms

But if B is scheduled when A switches context for IO operations, then CPU will not be idle and the scheduling will be:

A(8ms)-B(2ms)-A(8ms)-B(2ms)-A(8ms)-B(2ms)

When A goes for IO, B is scheduled and when B goes for IO, A is scheduled. Since IO operations take only 1ms of time, the processes stay in wait state for the other process to complete it's CPU time.

In this case, Total time taken (A and B) = 8+2+8+2+8+2 = 30ms

Hope this helps. Do Upvote! :)

Related Questions

Navigate

• Browse (All)
• Browse O
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.