Assignment 6: Design and Implement a CPU Profiler (Part 1)

Introduction

This project aims to design and implement a CPU profiling tool. The tool will be developed as a single kernel module that, when loaded, tracks statistics for each task on the system, such as total CPU time and the number of times a task is scheduled in and out. The module will display profiling results using the proc file system. This project is divided into two parts (A6 and A7) but will use and update the same kernel module code created in Part 1 (A6).

Recommended Background Reading

• Kprobes: documentation, examples
• x86_64 calling convention: documentation
• stack trace: source code, example
• spinlock: API
• Jenkins hash: API
• Time measurement (rdtsc): API
• Symbol look up: API

Part 1: Counting per task scheduling

[40 points] In part 1, you will design a kernel module that counts how many times a task has been scheduled onto the CPU. To achieve this, you will use Kprobes, a debugging tool in the Linux kernel that allows you to break at any kernel address. Kprobes can be configured to trigger when a specific function is executed, transferring control to an event handler routine.

Part 1.1. Setup procfs

[10 points] The results of the profiler tool should be displayed using the /proc file system. The first step is to create a /proc file for the profiler.

Tasks:

• Write a kernel module named perftop;
• perftop should create a /proc file named perftop;
• cat /proc/perftop should display "Hello World".

Deliverables:

• Load your perftop kernel module;
• Invoke cat /proc/perftop;
• Add a screenshot of the output from the above execution.

Part 1.2. Setup Kprobes

[15 points] Next, we will count the number of times the proc file we created in Part 1.1 (i.e., /proc/perftop) is opened using Kprobes.

Tasks:

• Understand the API for using Kprobes;
• Kprobes should call an event handler every time cat /proc/perftop is invoked;
• The event handler should increment a counter;
• The counter should be displayed by cat /proc/perftop.

Deliverables:

• Load your updated perftop kernel module;
• Invoke cat /proc/perftop 3 times;
• Add the screenshot of the three executions in the same window.

Part 1.3. Count the number of times a PID is scheduled in

[15 points] Next, we will count the times a PID has been scheduled. This will now track all PIDs on your Linux system.

Tasks:

• Setup a hash table with key as PIDs and value as the number of times that a specific PID has been scheduled;
• Setup a Kprobes hook on pick_next_task_fair function;
• Using the register calling convention, get the pointer of task_struct;
• Using the task_struct, extract the associated PID of the task;
• If the PID already exists in your hash table, then increment the value; otherwise, create a new hash table entry and set the value to 1;
• Modify the open function of the proc file to print (with cat /proc/perftop) the PIDs and their corresponding values (the number of times that PID was scheduled).

Deliverables:

• Load perftop module
• Invoke cat /proc/perftop
• Add screenshot of the output
• Upload the source code tarball