Consider three processes with the following characteristics: Process Period, T C
ID: 3813143 • Letter: C
Question
Consider three processes with the following characteristics:
Process
Period, T
Computation time, C
P1
4
2
P2
8
2
P3
32
5
Show how these three processes can be scheduled using the fixed priority, rate monotonic scheduling algorithm, with preemption. Apply the utilization-based schedulability test for this process set & comment on its outcome. Show the Gantt chart of your schedule time line.
Show how a cyclic executive could be constructed to implement the above three processes.
Perform the Response Time Analysis for this process set. Show all the steps clearly and discuss the results.
Process
Period, T
Computation time, C
P1
4
2
P2
8
2
P3
32
5
Explanation / Answer
rate-monotonic scheduling (RMS) is a priority assignment algorithm used in real-time operating systems (RTOS) with a static-priority scheduling class. The static priorities are assigned according to the cycle duration of the job, so a shorter cycle duration results in a higher job priority.
The schedulability test for RMS is:
{displaystyle U=sum _{i=1}^{n}{ rac {C_{i}}{T_{i}}}leq n({2}^{1/n}-1)}U= n(21/n-1)
where Ci is the computation time, Ti is the release period (with deadline one period later), and n is the number of processes to be scheduled.
In given example,
The utilization will be:
2/4 + 2/8 + 5/32 = 0.90625
The sufficient condition for {displaystyle 3,}3 processes, under which we can conclude that the system is schedulable is:
U= 3(21/3-1)= 0.77976...
Since, 0.90625 > 0.77976… the system is surely not schedulable.
But remember, this condition is not a necessary one. So we cannot say that a system with higher utilization is not schedulable with this scheduling algorithm.