CS 3733 Operating Systems

• Performance criteria for CPU schedulers
  • Fairness
  • Efficiency = CPU Utilization
  • Throughput = number of processes completed per unit time.
  • Turnaround Time = Time to execute a process from submission to termination.
  • Waiting Time
  • Response Time = Time between submission of a request to the first response.
  • Response Time Variance

• Scheduling algorithms for short term schedulers
  • First-Come-First Served (FCFS) is managed by a strict FIFO queue.
  • Shortest-Job-First (SJF) take the job which is shortest and run it next.
  • Non-preemptive Priority Scheduling
  • Preemptive Priority Scheduling
  • Round Robin Scheduling
  • Multi-Level Queues Classify jobs or processes and maintain separate queues for each class of processes. This can be managed in one of two ways:
    • Prioritize the queues and also take processes from the highest priority queues first.
    • Time-slice among queues. In this approach, each queue gets a an opportunity for a fixed share of the CPU time.
  • Multi-Level Feedback Queues defined by the following elements:
    • The number of queues.
    • The scheduling algorithm for each queue.
    • A method for determining when to upgrade a process to a higher priority queue.
    • A method of determining when to demote a process to a lower priority queue.
    • A method of determining which queue a process will enter when it needs service.