Question

Consider three CPU-intensive processes, which require 10,20 and 30 time units and arrive at times 0, 2, and 6, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling alogrithm? Do not count the context switches at time zero and at the end

Answer 1

Let three processes are $P_1,P_2$ and $P_3$

Process Arrival Time Burst Time

$P_1$ 0 10 $P_2$ 2 20 $P_3$ 6 30

The Gantt chart for SRTF scheduling algorithm

$P_1$

$P_2$

$P_3$

0 10 30 60

So there is only two context switches, at time unit 10 context switch form $P_1$ to $P_2$ and at time unit 30 context switch form $P_2$ to $P_3$.