xv6-signals-scheduler-os

Implementation of signal handling and custom scheduling in xv6. Features include signal delivery (SIGINT, SIGBG, SIGFG, SIGCUSTOM), a new process creation model with custom_fork and scheduler_start, a scheduler profiler for turnaround/waiting/response times, and a dynamic priority boosting scheduler with tunable α, β parameters.

xv6 Signals and Scheduler Project

📌 Overview

This project extends the xv6 operating system to enhance process management through:

• Signal handling for keyboard interrupts (Ctrl+C/B/F/G).
• A custom scheduler with new system calls.
• A scheduler profiler to measure performance metrics.
• A priority boosting scheduler with tunable parameters.

It demonstrates low-level systems programming, OS kernel modification, and performance optimization.

🚀 Features Implemented

🔹 Signal Handling in xv6

• Ctrl+C → SIGINT : Kills user processes (pid > 2).
• Ctrl+B → SIGBG : Suspends user processes.
• Ctrl+F → SIGFG : Resumes suspended processes.
• Ctrl+G → SIGCUSTOM : Invokes registered user-space signal handler if available.

🔹 Custom Scheduler Extensions

• custom_fork(start_later, exec_time)
  • Creates a process with deferred execution and limited run-time.
• scheduler_start()
  • Starts execution of all processes created with start_later = true.

🔹 Scheduler Profiler

• Reports per-process:
  • Turnaround Time (TAT)
  • Waiting Time (WT)
  • Response Time (RT)
  • Context Switches (#CS)

🔹 Priority Boosting Scheduler

• Dynamic priority model:
  πi(t) = πi(0) − α·Ci(t) + β·Wi(t)

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• Avoids starvation by boosting waiting processes.
• Tunable parameters α, β set in Makefile.

⚙️ Implementation Details

• Modified kernel files: proc.c, proc.h, syscall.c, trap.c, etc.
• Added system calls for signals and custom scheduling.
• Updated keyboard interrupt handler to generate signals.
• Integrated profiling counters into process structures.
• Implemented dynamic priority evaluation in the scheduler loop.

🧪 Testing

• CPU-bound Fibonacci test for signal handling.
• Parent-child processes for background/foreground control.
• Scheduler profiler validation using controlled workloads.
• Priority boosting effects compared for CPU-bound vs I/O-bound tasks.

▶️ How to Run

1. Clone xv6 repository with this project code.
2. Build and run inside QEMU:

make clean
make qemu
Run test programs (test1, test2, test_sched) to validate functionality.

Observe kernel logs for profiler and priority outputs.

📊 Results
Verified correct signal handling (Ctrl+C/B/F/G).

Scheduler profiler reports consistent metrics for TAT, WT, RT, #CS.

Priority boosting prevents starvation in I/O-heavy workloads.