CPU-Scheduling

1. AG Scheduling Algorithm

AG Scheduling (Adaptive General Scheduling) is a CPU scheduling algorithm that dynamically combines FCFS, Priority, and Shortest Job First (SJF) based on the execution phase of each process.

Each process is assigned a static time slice called Quantum.

The execution of a process is divided into three phases:

1. FCFS Phase – Non-preemptive execution for a fraction of its quantum.
2. Priority Phase – Preemptive execution based on priority for the next fraction of its quantum.
3. SJF Phase – Preemptive execution based on remaining burst time for the rest of its quantum.

---

Process Execution Rules

1. Quantum Usage:

   • The process runs according to its current phase (FCFS → Priority → SJF).
   • Quantum is updated based on whether the process completes or is preempted.

2. Scenarios:

   Scenario 1: The running process used all its quantum and still has remaining burst:

   • Move to end of ready queue.
   • Increase quantum by 2.

   Scenario 2: Process executed during Priority phase and was preempted:

   • Move to end of ready queue.
   • Increase quantum by ceil(remainingQuantum / 2).

   Scenario 3: Process executed during SJF phase and was preempted:

   • Move to end of ready queue.
   • Increase quantum by remaining quantum.

   Scenario 4: Process completed before using all its quantum:

   • Set quantum to 0.

---