Recall that Shortest Remaining Time First (SRTF) is a variant of Shortest Job Fi
ID: 3856365 • Letter: R
Question
Recall that Shortest Remaining Time First (SRTF) is a variant of Shortest Job First (SJF) with preemption added in. Consider the following three processes
for the CPU. The scheduler uses SRTF. The scheduler re-evaluates which process to run only upon the arrival of a new process into the
scheduling queue, or the completion of a process. The table shows the arrival time of each process.
Process
Arrival Time
Execution Time
P1
T0
5 ms
P2
T0 + 2 ms
4 ms
P3
T0 + 3 ms
1 ms
The scheduling starts at time T0.
Fill up the blank cell/cells in the table below with the appropriate time information.
(a) At time T0: (2 points)
Process
Remaining Time
P1
P2
Not Arrived Yet
P3
Not Arrived Yet
(b) At time T0 + 2 ms : (Process P2 arrives) (4 points)
Process
Remaining Time
P1
P2
P3
Not Arrived Yet
(c) At time T0 + 3 ms: (Process P3 arrives) (4 points)
Process
Remaining Time
P1
P2
P3
(d) Fill in the table below with the process that is executing on the processor during each time slot (the first slot has been filled up with Process P1). (10 points)
Interval T0 +
0 ms
1 ms
2 ms
3 ms
4 ms
5 ms
6 ms
7 ms
8 ms
9 ms
10 ms
11 ms
12 ms
Running Process
P1
Process
Arrival Time
Execution Time
P1
T0
5 ms
P2
T0 + 2 ms
4 ms
P3
T0 + 3 ms
1 ms
Explanation / Answer
A)
PROCESS
REMAINING TIME
P1
5ms
P2
NOT ARRIVED YET
P3
NOT ARRIVED YET
Process p1 just arrived but complete execution left
B)
PROCESS
REMAINING TIME
P1
3ms
P2
4ms
P3
NOT ARRIVED YET
After 2 s , process p1 compete its 2ms execution and left is 3ms.
Process p2 just arrived so complete execution left
C)
PROCESS
REMAINING TIME
P1
2ms
P2
4ms
P3
1ms
After 2 s , process p1 compete its 2ms execution and left is 3ms .
Process p2 just arrived at 2ms but completion time for p1 is less than p2, so p1 will execute and after 3ms, p1 remaining time is 2ms.
Process p2 compete un utilized so execution time is 4ms
Process p3 just arrived so complete execution left
Interval time
0 ms
1 ms
2m
3ms
4ms
5ms
6ms
7ms
8ms
9ms
10ms
11ms
12ms
Running process
P1
P1
P1
P3
P1
P1
P1
P2
P2
P2
P2
PROCESS
REMAINING TIME
P1
5ms
P2
NOT ARRIVED YET
P3
NOT ARRIVED YET
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