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Assignment Brief - CPU Scheduling
Introduction
The aim of this assignment is to investigate the performance of different CPU scheduling algorithms. You will use a discrete event simulator to conduct experiments on different processor loads and schedulers, and analyse the results to determine in which situations each scheduling algorithm works most efficiently. You will then write a report on your experiments, communicating your findings in an effective manner.
Learning Outcomes
Upon successful completion of this assignment you will have a good understanding around the development of CPU scheduling, and be able to demonstrate, through simulations, strengths and weaknesses of different scheduling algorithms. Moreover, you will demonstrate that you can write a scientific report describing the design and execution of experiments and present the experimental data into a format suitable for comparison.
Getting Started
1. Download the os-coursework1.zip archive Download os-coursework1.zip archiveand unzip it into your workspace.
2. Open the project with IntelliJ. The project should contain several .java files stored under the src/main/java directory.
3. Compile and run the code. This should work without problems. Note that the source code contains two classes with main methods, namely Simulator and InputGenerator.
Simulator
The simulation framework that is contained in os-coursework1.zip consists of two components:
input generator
simulator
The flow of using these two tools is as follows:

Input Generator
The input generator can be run either through IntelliJ or, directly, from the command line.
As mentioned above, the project contains two main Java classes, therefore you will have to create two separate run configurations and set the arguments discussed below. IntelliJ will automatically create a default configuration if you right-click --> run a specific main class.
Running the input generator through the command line can be done in different ways; the simplest would be to generate a .jar file through IntelliJ. You are working with maven projects, therefore you can execute the mvn package goal which will, by default, generate a .jar file named os-coursework1-1.0-SNAPSHOT.jar under the target folder. Subsequently you can run the InputGenerator with the following command from the base project folder (os-coursework1):
java -cp target/os-coursework1-1.0-SNAPSHOT.jar InputGenerator experiment1/input_parameters.prp experiment1/inputs.in
This will generate an input data file in ../experiment1/inputs.in based on the parameters provided in the property file ../experiment1/input_parameters.prp.
The property file contains several parameters to specify (1) the number of processes, (2) their static priority, (3) the mean inter-arrival time for processes, (4) the average duration of CPU and (5) the average duration of I/O bursts and (6) the number of these bursts, as well as (7) a seed for the simulator. The total number of parameters is 7.
You can look at this short guide Download this short guideon exponential distributions, if you are interested in understanding how these pseudorandom values are produced in the code.
You will have to run your simulations (see Simulator section below) using different seeds (e.g. 5 different seeds would be a good choice) to make sure that your conclusions are robust. A seed is used to initialise (i.e. seed) the pseudorandom number generator which is integral in running a simulation. If you run a simulation with the same seed and input data, you will always get the same output. You will have to change the seed, in order to influence the pseudonumber generator and, therefore, the input data and simulation (see here for a good discussion on seedsLinks to an external site.).
The generated input data file contains a line for each process with the first value being the static priority and the second value the arrival time. The remaining values are the durations of alternating CPU and I/O bursts (the number of these values is always odd because we always start and finish with a CPU burst). For example:
0 0 15 5 15 5 15
0 10 50
0 25 5
Note that you can write such input files manually in order to understand the behaviour of the simulator and to test your implementation. For example, you can use the workloads discussed during the lectures.
Simulator
As with the input generator, the simulator can be run through IntelliJ (remember to add the arguments in the run configuration) or the command line. The command to run the simulator using the jar file created as discussed above is:
java -cp target/os-coursework1-1.0-SNAPSHOT.jar Simulator experiment1/simulator_parameters.prp experiment1/output.out experiment1/inputs.in
where experiment1 is the subfolder included in the .zip file.
This will generate an output file in ../experiment1/output.out (1) based on the parameters provided in the property file experiment1/simulator_parameters.prp and (2) using the input data file experiment1/inputs.in. Note that you can supply several input files. The contents of all supplied files will be considered when running the simulation.
The property file contains parameters that define how the experiment is run:
1.the scheduler class to use
2.a potential time limit (timeLimit) on the duration of the simulation
3.the duration of interrupts, including scheduler invocations (interruptTime)
4.parameters that are needed for the scheduling algorithms. These are timeQuantum, initialBurstEstimate, alphaBurstEstimate and will be defined below in the specification of the schedulers.
The most important classes are the Process class and the AbstractScheduler classes which concrete scheduler implementations extend. You are provided with the implementation of a First-Come, First-Served scheduler (see FcfsScheduler.java) in the provided IntelliJ project.
An output file looks as follows:

You can copy and paste the content of this file into any spreadsheet program in order to perform further analysis of this output data or use an appropriate language for that (e.g. R, Matlab, Python etc). We assume that the unit of time is ms throughout this coursework. The simulator logs the events that it executes to the terminal as follows (the number before the colon is the point in time when the event happens):
0: CREATE process 1
10: CREATE process 2
15: BLOCK process 1
20: UNBLOCK process 1
25: CREATE process 3
65: TERMINATE process 2
80: BLOCK process 1
85: UNBLOCK process 1
85: TERMINATE process 3
100: TERMINATE process 1
Your Implementation
As part of this project you will need to write Java code for:
1. calculating the performance metrics (as defined in the lectures) by completing the corresponding functions in the file Process.java.
turnaround time of the process: getTurnaroundTime()
waiting time: getWaitingTime()
response time: getResponseTime()
Remark: These functions are called by the simulator when a process terminates to produce the output file. You will be able to compute CPU utilisation and throughput, separately, by analysing the output data.
2. the following scheduling algorithms by completing the corresponding .java files. You will have to override some methods from the AbstractScheduler class -- read carefully their documentation in the source code:
Round Robin (RRScheduler.java) - Read the timeQuantum from the parameters. The scheduler is non-preemptive*.
Ideal Shortest Job First (IdealSJFScheduler.java) - You can use the getNextBurst() method to get the duration of the next burst for each process. The scheduler is non-preemptive.
Multi-level feedback queue with Round Robin (FeedbackRRScheduler.java) - The easiest way to compute a multi-level queue is to use a priority queue where priorities correspond to the levels (lower number means higher priority). Implement the following feedback: a process is demoted if it used its full time slice. The scheduler is preemptive.
Shortest Job First using exponential averaging (SJFScheduler.java) - Read the initialBurstEstimate ( 0) and alphaBurstEstimate ( ) from the parameters. For each process, use exponential averaging to estimate the duration of the process' next burst (which will then define the priority of the process) from its previous burst durations. You can use the getRecentBurst() method to get the duration of the most recent CPU burst of a process. The scheduler is non-preemptive.
You may add debug output to your implementation. Make sure that you print to System.out only.
Remark: Note that there are placeholders, as TODO comments, in the code, where you are expected to add code. You may have to create new or override existing methods as well - all abstract methods in the AbstractScheduler class must be overridden, otherwise your code won't compile. The implementation of the schedulers should be based on the material discussed in the lectures, where they are clearly defined. Do NOT alter the structure of the given classes but only add code where deemed necessary.
*Important: here we say that the RR scheduler is non-preemptive which contradicts what was presented in the lecture. This is because the simulator considers as preemptive a scheduler that will preempt a running process only when a process (new or previously blocked) appears in the ready queue, but not when the allocated time quantum is consumed by a process. Dealing with completed time quanta is done at a different point in the code (setRunning() in the BurstProcess class). The RR scheduler will therefore be dealt with as non-preemptive here, as described above.
Your Experiments
Using the simulator and the schedulers you developed, set up three experiments to investigate three different aspects of scheduling algorithms. You are free to choose which aspects you target - it is important that you clearly explain in your report what the specific purpose of each experiment is and which conclusions your draw from the experimental data that you gather.
General questions of interest are for instance:
How does the process characteristics affect the choice of a good scheduling algorithm?
What is the influence of the workload?
What is the effect of the scheduling algorithm parameters?
How does the cost for running the scheduler affect performance?
Remarks: You will have to adjust the workload (CPU utilisation) of your input data by finding appropriate combinations of parameter values for the input generator. Hint: The CPU time of the idle process (process ID 0) tells you something about the CPU utilisation. It is important to present averaged results over several input data sets created using different random seed values. Note that we ask you to investigate specific aspects related to the given schedulers, so the experiments should be designed in a way that each experiment includes all schedulers. Running one experiment (e.g. by changing a specific parameter) using three schedulers does not mean that you are running three experiments!
Your Report
The report should have the following format:
Introduction.
Describe what you are trying to do in this experiment.
Methodology. Describe the experimental setup.
Describe the experiments you have performed. For each experiment, clearly state:
othe parameters you used to generate the input data (all of them, even if you only alter a subset of these for an experiment)
othe parameters you used to run the simulator (all of them, even if you only alter a subset of these for an experiment)
othe corresponding names of input and output files in your submission
Discuss the metrics you have chosen to use and the rationale behind your selection
Discuss how you validated that your experiments produce reasonable results
Results. Present your results in such a way that the reader can draw direct comparisons between schedulers. Use graphs to visualise your results. Tables are also acceptable but graphs are preferable.
Discussion. Explain how your experimental results support or challenge your hypotheses. Every claim must be supported by evidence - explicitly refer to graphs and tables in the Results section.
Threats to validity. Mention any reservations, caveats or biases that may have affected the outcome of your experiments.
Conclusions. Summarise what you have achieved and which insights you gained.
There is no lower or upper word limit. Be as concise as possible and as verbose as necessary. As a rough guide, the Introduction and Methodology sections should be one page long. The Results section should be 2 - 4 pages long (most of which should be graphs and tables). The remaining sections should be around one page in total.
Submission
Submission is on Canvas. You should submit a single .zip file (named cand_num.zip, where cand_num is your candidate number) with the following contents:
report.pdf - the report as discussed above (in pdf format)
os-coursework1/
oexperimentk (for $k = 1 ... 3)
all parameter property files for the simulator used in experiment k
all parameter property files for the input generator used in experiment k
all input files (.in) generated for experiment k
all output files (.out) produced in experiment k
osrc/
all .java files that were contained in os-coursework1.zip, including the 5 files that you modified.
run.sh or run.bat: a script to automatically reproduce the files in output/ from the files in input/ and corresponding parameters.prp files for each experiment
You will not receive any marks for your submission if your code does not compile. You will receive a penalty of 10 marks if your project does not respect the above structure, or if the run.sh or run.bat files cannot reproduce your output files.
It should be straightforward to write a simple script that automatically runs all three experiments, and it would be useful for you as well e.g. for testing purposes. See hereLinks to an external site. on how to write a shell script and hereLinks to an external site. on how to write a bat script for windows.
Marking Criteria
There is a total of 100 marks that will be distributed as follows:
Your Implementation [55/100]
1. Performance metrics [9/55]
Turnaround time [3/9]
Waiting time [3/9]
Response time [3/9]
2. Scheduling algorithms [46/55]
Round Robin [8/46]
Ideal Shortest Job First [10/46]
Multi-level feedback queue with Round Robin [13/46]
Shortest Job First using exponential averaging [15/46]
You get zero marks for your implementation if your code does not compile or files are missing.
Your Experiments and Your Report [45/100]
General form of report (e.g. structure, use of language) [6/45]
Experiment 1 [13/45]
Scope and objectives well-defined [4/13]
Parameters and setup explained [3/13]
Results visualised [3/13]
Results discussed [3/13]
Experiment 2 [13/45]
Scope and objectives well-defined [4/13]
Parameters and setup explained [3/13]
Results visualised [3/13]
Results discussed [3/13]
Experiment 3 [13/45]
Scope and objectives well-defined [4/13]
Parameters and setup explained [3/13]
Results visualised [3/13]
Results discussed [3/13]
You will receive a penalty of 10 marks if your input files and output files are not in the submission archive. Note that by the character of the assignment it is very unlikely that any two submissions use the same set of input files.
Plagiarism and Collusion
The coursework you submit is supposed to have been produced by you and you alone. This means that you should not:
work together with anyone else on this assignment
give code for the assignment to other students
request help from external sources
do anything that means that the work you submit for assessment is not wholly your own work, but consists in part or whole of other people’s work, presented as your own, for which you should in fairness get no credit
use any generative AI tool for generating source and/or text. Note that we will use tools that can detect plagiarised code, which means that it is very likely to find out about ChatGPT-generated code very easily.
If you need help ask your tutor. The University considers it misconduct to give or receive help other than from your tutors, or to copy work from uncredited sources, and if any suspicion arises that this has happened, formal action will be taken. Remember that in cases of collusion (students helping each other on assignments) the student giving help is regarded by the University as just as guilty as the person receiving help, and is liable to potentially receive the same penalty. Also bear in mind that suspicious similarities in student code are surprisingly easy to spot and sadly the procedures for dealing with it are stressful and unpleasant. Academic misconduct also upsets other students, who do complain to us about unfairness. So please don’t collude or plagiarise.