SJF is frequently used for long term scheduling. It reduces the average waiting time over FIFO (First in First Out) algorithm. SJF method gives the lowest average waiting time for a specific set of processes. It is appropriate for the jobs running in batch, where run times are known in advance.
Full Answer
What is the formula for calculating the average waiting time in FIFO?
FIFO (cont.) •Suppose that the processes arrive in order P 2, P 3, P 1 •The Gantt chart for the schedule: •Waiting time for P 1 =6;P 2= 0;P 3 = 3 •Average waiting time: (6 + 0 + 3)/3 = 3 P 2P 3P 1
What is SJF’s average response time?
•SJF’s average response time (all 3 jobs arrive at same time) •(0 + 5 + 10)/3 = 5 Y. Cheng GMU CS571 Spring 2021 43 Waiting, Turnaround, Response 44 P 1P 3P 2 [P2, P3 arrive at 15] P 1 P1’s waiting time: P2’s turnaround time: P3’s response time: 0 25 35 45 120 Y. Cheng GMU CS571 Spring 2021 Waiting, Turnaround, Response 45 P 1P 3P 2P 1
What is the turnaround time for round robin and FIFO?
In your first try, you have processes running in parralel. This would assume 2 processors. But if 2 processors are available, the round robin and the fifo would have the same result, as there are always enough processors for serving the active proceeses (thus no waiting time). The total turnaround would be 9 and the average 1,8.
Which is better for turnaround time - RR or SJF?
Tradeoff Consideration •Typically, RR achieves higher average turnaround time than SJF, but better response time •Turnaround time only cares about when processes finish
What is the average turnaround time using SJF?
Turnaround Time = Total Turnaround Time- Arrival Time P1 = 28 – 0 =28 ms, P2 = 5 – 1 = 4, P3 = 13 – 2 = 11, P4 = 20 – 3 = 17, P5 = 8 – 4 = 4 Total Turnaround Time= 64 mills.
Is shortest job first same as shortest remaining time first?
Processes having same arrival time will convert SRTF to SJF....Differences:Shortest Job First:Shortest Remaining Job First:It is a non-preemptive algorithm.It is a preemptive algorithm.It involves lesser number of context switching.It involves higher number of context switching.6 more rows•Mar 22, 2021
Which scheduling algorithm has shortest turnaround time?
Shortest Job First (SJF) is an algorithm in which the process having the smallest execution time is chosen for the next execution. This scheduling method can be preemptive or non-preemptive. It significantly reduces the average waiting time for other processes awaiting execution.
How is turnaround time calculated in SJF scheduling?
Turnaround time = Exit time - Arrival time For example, if we take the First Come First Serve scheduling algorithm, and the order of arrival of processes is P1, P2, P3 and each process is taking 2, 5, 10 seconds.
Is SJF preemptive and SRTF same?
In a non-preemptive kernel, this is known as SJF, shortest-job first. This means that all processes waiting in the ready state queue are evaluated, and whichever is deemed to be the shortest will move to the front of the line. In a preemptive kernel this algorithm is known as SRTF, shortest remaining time first.
What is the difference between SJF preemptive and non-preemptive?
Non-preemptive scheduling is called rigid as even if a critical process enters the ready queue the process running CPU is not disturbed....Comparison Chart:ParameterPREEMPTIVE SCHEDULINGNON-PREEMPTIVE SCHEDULINGResponse TimePreemptive scheduling response time is less.Non-preemptive scheduling response time is high.9 more rows•May 27, 2022
What is the drawback of SJF algorithm?
Disadvantages of SJF Used for long-term scheduling in a batch system. Can't implement this algorithm for CPU scheduling for the short term as we can't predict the length of the upcoming CPU burst. Cause extremely long turnaround times or starvation. Knowledge about the runtime length of a process is necessary.
What will be the average waiting time if the CPU scheduling policy is SJF with preemption?
Non Pre-emptive Shortest Job First We scheduled the same set of processes using the First come first serve algorithm in the previous tutorial, and got average waiting time to be 18.75 ms , whereas with SJF, the average waiting time comes out 4.5 ms .
Which one is the best between SJF and Round Robin in terms of response time explain with example?
Shortest Job First (SJF) executes the processes based upon their burst time i.e. in ascending order of their burst times. Round-Robin (RR) executes the processes based upon the time quantum defined i.e. each process is executed for a fixed amount of time.
What is the average turnaround time?
The turnaround time is the interval from the time of submission to the time of completion. More specifically, turnaround time is the sum of the periods spent waiting to get into memory, waiting in the ready queue, executing on the CPU, and doing I/O.
What is difference between turnaround time and response time?
Turnaround Time vs Response Time: Turnaround time is the amount of time elapsed from the time of submission to the time of completion whereas response time is the average time elapsed from submission until the first response is produced.
What is the difference between lead time and turnaround time?
TAT is frequently associated with Lead Time but differs from it in that the Lead measures the time between receipt of an order and final delivery, while the TAT measures the time spent between production of the product and final delivery.
Average Turnaround Time
Avg. Turnaround Time = Total Turnaround Time / No.of Process = 64 / 5 = 12.8 mills.
Advantages
It is the optimal algorithm ; it gives minimum average waiting time for a given set of processes.
Disadvantages
The real difficulty with the SJF algorithm is to know the length of next CPU request.
What is SJF algorithm?
SJF is an algorithm in which the process having the smallest execution time is chosen for the next execution.
What are the two types of SJF?
There are basically two types of SJF methods 1) Non-Preemptive SJF and 2) Preemptive SJF. In non-preemptive scheduling, once the CPU cycle is allocated to process, the process holds it till it reaches a waiting state or terminated. In Preemptive SJF Scheduling, jobs are put into the ready queue as they come.
What is Shortest Job First Scheduling?
Shortest Job First (SJF) is an algorithm in which the process having the smallest execution time is chosen for the next execution. This scheduling method can be preemptive or non-preemptive. It significantly reduces the average waiting time for other processes awaiting execution. The full form of SJF is Shortest Job First.
What is preemptive SJF scheduling?
In Preemptive SJF Scheduling, jobs are put into the ready queue as they come. A process with shortest burst time begins execution. If a process with even a shorter burst time arrives, the current process is removed or preempted from execution, and the shorter job is allocated CPU cycle.
What happens when a process has a short burst time?
Although a process with short burst time begins, the current process is removed or preempted from execution, and the job which is shorter is executed 1st.
Which method gives the lowest average waiting time for a specific set of processes?
SJF method gives the lowest average waiting time for a specific set of processes.
What is the step 0 of P4?
Step 0) At time=0, P4 arrives and starts execution.
Which has the advantage of having a minimum average waiting time among all scheduling algorithms?
Shortest Job first has the advantage of having a minimum average waiting time among all scheduling algorithms.
What is the shortest job first?
Shortest job first (SJF) or shortest job next, is a scheduling policy that selects the waiting process with the smallest execution time to execute next. SJN is a non-preemptive algorithm. Shortest Job first has the advantage of having a minimum average waiting time among all scheduling algorithms. It is a Greedy Algorithm.
Is turn around time the same as completion time?
In this post, we have assumed arrival times as 0, so turn around and completion times are same.
Can you predict execution time?
While it is not possible to predict execution time, several methods can be used to estimate the execution time for a job, such as a weighted average of previous execution times. SJF can be used in specialized environments where accurate estimates of running time are available.
What is the SJF algorithm?
1. Shortest Job First (SJF) : Shortest Job First (SJF) Scheduling Algorithm is based upon the burst time of the process. The processes are put into the ready queue based on their burst times. In this algorithm, the process with the least burst time is processed first.
What is the advantage of SJF?
The major advantage of this algorithm is that all processes get executed one after the other which does not lead to starvation of processes or waiting by process for quite long time to get executed. Shortest Job First (SJF) executes the processes based upon their burst time i.e. in ascending order of their burst times.
Is SJF preemptive or non-preemptive?
SJF is also non-preemptive but its preemptive version is also there called Shortest Remaining Time First (SRTF) algorithm. Round-Robin (RR) is preemptive in nature. The average waiting time for given set of processes is minimum. The average waiting time for given set of processes is quite small and depends on the time quantum.
