Operating System CPU Scheduling Basics Quiz

CPU Scheduling

• The main responsibility of the CPU scheduler is to allocate the CPU time to processes.
• The CPU scheduler makes scheduling decisions under the following conditions:
  • When a process switches from running to waiting state
  • When a process switches from waiting to ready state
  • When a process terminates

Dispatcher Role

• The role of the dispatcher in CPU scheduling is to:
  • Context switch (i.e., switch the CPU to another process)
  • Perform process switching
  • Save the state of the previously running process
  • Restore the state of the newly scheduled process

Scheduling Types

• Non-preemptive scheduling occurs when the operating system does not interrupt a process while it is executing.
• CPU-I/O burst cycle: A process executes a CPU burst (uses the CPU), then performs I/O operations, and then repeats this cycle during its execution.

CPU Utilization

• The maximum CPU utilization obtained with multiprogramming is typically 90% or higher.

First-Come, First-Served (FCFS) Scheduling

• Optimization criterion: Minimize average waiting time.
• Average waiting time under the FCFS policy:
  • Increases as the process arrival order changes
  • May be significantly affected by a high variation in process CPU-burst times
• Main disadvantage of the FCFS scheduling algorithm: It can cause convoy effect (many I/O-bound processes waiting for a CPU-bound process).
• Main advantage: Simple to implement.
• In a dynamic situation with one CPU-bound process and many I/O-bound processes, the FCFS scheduling algorithm may cause the CPU-bound process to monopolize the CPU.
• In a dynamic situation with many I/O-bound processes, the FCFS scheduling algorithm may cause many I/O-bound processes to wait for the completion of a CPU-bound process.