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Scheduling: Introduction
Homework

1. Workload Assumptions

2. Scheduling Metrics

3. First In, First Out (FIFO)

4. Shortest Job First (SJF)

5. Shortest Time-to-Completion First (STCF)

6. A New Metric: Response Time

7. Round Robin

8. Incorporating I/O

9. Homework (Simulation)

Question & Answer

1. Compute the response time and turnaround time when running three jobs of length 200 with the SJF and FIFO schedulers

FIFO:

SJF:

2. Now do the same but with jobs of different lengths: 100, 200, and 300.

2.1

FIFO: 100 200 300

SJF: 100 200 300

2.2

FIFO: 300 200 100


SJF: 300 200 100

3. Now do the same, but also with the RR scheduler and a time-slice of 1.

4. For what types of workloads does SJF deliver the same turnaround times as FIFO?

When the workload doesn’t arrive from large to small.

5. For what types of workloads and quantum lengths does SJF deliver the same response times as RR?

The RR scheduling strategy is to execute a time slice in sequence in the job list, let the length of the time slice be T, then the response time of the Nth job is (N-1) * T, and SJF needs to finish one job before executing another job. Therefore, the execution time of each job of the SJF strategy should be equal to the time slice of the RR strategy.

6.What happens to response time with SJF as job lengths increase? Can you use the simulator to demonstrate the trend?

When the job length increases, the waiting response time for subsequent jobs will increase accordingly.

7. What happens to response time with RR as quantum lengths increase? Can you write an equation that gives the worst-case response time, given N jobs?

Assuming the length of the time slice is T, the response time of the Nth job = （N - 1）* T.
When the quantum lengths increase, the response time will increase accordingly.