Consider a system running 10 I/O bound task and one CPU bound task. Assume that I/O bound issues an I/O operation once for every milisecond of CPU computing and that each I/O operation 10 miliseconds to complete. Also assume that the context switching overhead is 0, 1 milisecond and that all processes are long running task. what is the CPU utilization for round robin schedular when :

(i) the time quantum is 1 milisecond

(ii) the time quantum is 10 miliseconds?

Solution:

(i) the time quantum is 1 milisecond:

Irrespective of which process is scheduled, the scheduler incurs a 0.1 millisecond context-switching cost for every context-switch.

This results in a CPU utilization of, $$\frac{1}{1.1} * 100=91 \%$$

(ii) the time quantum is 10 miliseconds?

The I/O-bound tasks incur a context switch …