Lecture Operating systems: Lesson 17 - Dr. Syed Mansoor Sarwar

Lecture Operating systems: Lesson 17 - Dr. Syed Mansoor Sarwar. The main topics covered in this lesson include: multilevel queues and multilevel-feedback-queue scheduler, multi-level queues scheduling, multi-level feedback queues scheduling, UNIX System V scheduling, algorithm evaluation, . | Operating Systems Lecture 17 Syed Mansoor Sarwar Agenda for Today Review of previous lecture Multi-level queues scheduling Multi-level feedback queues scheduling UNIX System V scheduling Algorithm evaluation Recap of lecture 28 April 2022 Copyright Virtual University of Pakistan Review of Lecture 16 Shortest-Job-First is optimal Round-Robin scheduling Multi-level queues scheduling 28 April 2022 Copyright Virtual University of Pakistan Multilevel Queues 28 April 2022 Copyright Virtual University of Pakistan Multilevel Feedback Queues A process can move between the various queues aging can be implemented this way. Multilevel-feedback-queue scheduler defined by the following parameters Number of queues Scheduling algorithms for each queue 28 April 2022 Copyright Virtual University of Pakistan Multilevel Feedback Queues Method used to determine when to upgrade a process Method used to determine when to demote a process Method used to determine which queue a process will enter when that process needs service 28 April 2022 Copyright Virtual University of Pakistan Multilevel Feedback Queues 28 April 2022 Copyright Virtual University of Pakistan UNIX System V Scheduling Algorithm Multilevel feedback priority queues with round robin within each queue Quantum 1 second Priorities are divided into two groups bands Kernel Group User Group 28 April 2022 Copyright Virtual University of Pakistan UNIX System V Scheduling Algorithm Priorities in the Kernel Group are assigned in a manner to minimize bottlenecks processes waiting in a lower-level routine get higher priorities than those waiting at relatively higher-level routines. 28 April 2022 Copyright Virtual University of Pakistan UNIX System V Scheduling Algorithm In decreasing order of priority the bands are Swapper Block I O device control processes File manipulation Character I O device control processes User processes 28 April 2022 Copyright Virtual University of Pakistan UNIX System V Scheduling Algorithm Priorities of .