Priority Scheduling

In Morinaga OS, optimizing system performance is crucial, especially when running resource-intensive applications. One effective method is adjusting the niceness of processes to prioritize critical tasks. This section explains how to change the niceness of a process, handled by a user-space daemon called Watson running under X11.

Understanding Niceness

In Unix-like operating systems, niceness is a value that influences process scheduling priority. A lower niceness value means higher priority. Adjusting niceness allows the system to allocate more CPU time to important processes.

Watson: Managing Process Priorities

Watson is a background process that monitors the active window in the X11 environment. It adjusts the niceness of the currently focused application to improve responsiveness. Here's how Watson operates:

1. Detects the active window using X11 APIs.
2. Retrieves the process ID (PID) associated with the window.
3. Adjusts the niceness of the process using system calls.

Implementation Details

Below is a simplified Python script illustrating how Watson can adjust process niceness:

import time
import subprocess
import os

def get_active_window_pid():
    # Use xprop to get the active window ID
    window_id = subprocess.check_output(['xprop', '-root', '_NET_ACTIVE_WINDOW']).decode()
    window_id = window_id.strip().split()[-1]

    # Use xprop to get the PID of the window
    pid = subprocess.check_output(['xprop', '-id', window_id, '_NET_WM_PID']).decode()
    pid = pid.strip().split()[-1]
    return int(pid)

def adjust_niceness(pid):
    # Reset niceness of all processes
    subprocess.call(['renice', '0', '-u', os.getlogin()])
    # Set niceness of the active process to -10
    subprocess.call(['renice', '-10', '-p', str(pid)])

def main():
    previous_pid = None
    while True:
        try:
            active_pid = get_active_window_pid()
            if active_pid != previous_pid:
                adjust_niceness(active_pid)
                previous_pid = active_pid
            time.sleep(1)
        except Exception as e:
            print(f"Error: {e}")
            time.sleep(1)

if __name__ == "__main__":
    main()

Note: This script requires appropriate permissions to adjust process priorities. It should be run with the necessary privileges or capabilities.

Running Watson at Startup

To ensure Watson runs automatically:

1. Create a systemd service file /etc/systemd/system/watson.service with the following content:

[Unit]
Description=Watson Priority Manager
After=graphical.target

[Service]
Type=simple
ExecStart=/usr/local/bin/watson.py
User=root
Environment=DISPLAY=:0

[Install]
WantedBy=graphical.target

2. Enable and start the service:

sudo systemctl enable watson.service
sudo systemctl start watson.service