Multi Level Queue Scheduling (MLQ)

Multi Level Queue Scheduling (MLQ)

· Multilevel queue scheduling classifies the processes according to their types for example, a multilevel queue scheduling algorithm makes a common.

· In this scheduling ready queue is divided into various queue that are called sub queues. A subqueue is a distinct operational queue

· The process are permanently assigned to subqueues, generally based on some property of the process such as memory size,priority or process type

· Each subqueue has its process sucheduling algorithm. For example interactive process at the foreground may use round robin scheduling while batch jobs at the background may use the FCFS method

· For example, consider a system with four different queues

1. System processes

2. Interactive processes

3. End-user processes

4. Interactive processes

· In this example, each queue has absolute priority absolute over low priority queues. No process in a batch queue could run unless the queue for system process and interactive processes were all empty.

· If an interactive process entered the ready queue while a batch process was running the batch process would be preempted. For example,solaries 2 operating system uses this form of algorithm

Example Problem :
Consider below table of four processes under Multilevel queue scheduling.Queue number denotes the queue of the process.

Priority of queue 1 is greater than queue 2. queue 1 uses Round Robin (Time Quantum = 2) and queue 2 uses FCFS.

Below is the gantt chart of the problem :

At starting both queues have process so process in queue 1 (P1, P2) runs first (because of higher priority) in the round robin fashion and completes after 7 units then process in queue 2 (P3) starts running (as there is no process in queue 1) but while it is running P4 comes in queue 1 and interrupts P3 and start running for 5 second and after its completion P3 takes the CPU and completes its execution.

Advantages:

The processes are permanently assigned to the queue, so it has advantage of low scheduling overhead.

Disadvantages:

Some processes may starve for CPU if some higher priority queues are never becoming empty.
It is inflexible in nature.

Comments

Defination of OS(operating system) and its concepts

What do you mean by operating system? Definition : An operating system is a program that act as an interface between the user of a computer and the Computer hardware. Operating system is a first program that gets loaded into the memory through a process called booting. Concepts of operating system : · The purpose of operating system is to provide an environment in which a user can execute program in a convenient and efficient manner. · Operating system is an integrated set of program that ma...

Scheduler

Scheduler Scheduling Objectives Here, are important objectives of Process scheduling Maximize the number of interactive users within acceptable response times. Achieve a balance between response and utilization. Avoid indefinite postponement and enforce priorities. It also should give reference to the processes holding the key resources Process Scheduling handles the selection of a process for the processor on the basis of a scheduling algorithm and also the removal of a process from the processor. It is an important part of multiprogramming in operating system. Process scheduling involves short-term scheduling, medium-term scheduling and long-term scheduling. Details about these are given as follows − Long-Term Scheduling Long-term scheduling involves selecting the processes from the storage pool in the secondary memory and loading them into the ready queue in the main memory for execution. This is handled by the long-term scheduler or job scheduler. The long-term s...

Multi user Operating System

Multi user operating system · In a multi-user operating system, multiple number of user can access different resources of a computer at a same time. · The access is provided using a network that consists of various personal computer attached to a mainframe computer system. diagram of multi -user operating system · The various personal computer can send and receive information to mainframe computer system. · The example of multi-user OS are UNIX, windows 2000,novell netware. sing...

Exokernel architecture

Exokernel architecture Most of us know what kernels are and how do they work to make programmers’ lives easier. But, how many of us know what exokernels are? I hope you will be able to get a brief introduction on this terminology through this blog. Let’s start with a brief introduction on kernel. What is a kernel? A kernel is the foundational layer of an operating system that functions at a basic level, communicating with hardware and managing resources, such as CPU and the memory. It works as an interface between the user application and the hardware. There are two main types of kernel 1. Micro kernel 2. Monolithic Kernel 1. Monolithic architecture 2. Layerd archtecture . 3. Virtual machine architecture 4. Exokernel architecture 5. Client server architecture 6. Micro kernel architecture Now let’s head into our main focus. What is an Exokern...

CPU Scheduling

CPU Scheduling What is CPU Scheduling? CPU Scheduling is a process of determining which process will own CPU for execution while another process is on hold. The main task of CPU scheduling is to make sure that whenever the CPU remains idle, the OS at least select one of the processes available in the ready queue for execution. The selection process will be carried out by the CPU scheduler. It selects one of the processes in memory that are ready for execution. Types of CPU Scheduling Here are two kinds of Scheduling methods: Preemptive Scheduling In Preemptive Scheduling, the tasks are mostly assigned with their priorities. Sometimes it is important to run a task with a higher priority before another lower priority task, even if the lower priority task is still running. The lower priority task holds for some time and resumes when the higher priority task finishes its execution. Non-Preemptive Scheduling In this type of scheduling method, the CPU has been allocated to ...

Easytolearn

Search This Blog