Summary :- Distributed Process Scheduling

Prepared BY:-

JAYA KALIDINDI

Summary of chapter 5

A System performance model Static process scheduling Dynamic load sharing and balancing Distributed process implementation Real time scheduling

A system performance model[2]

Depicts the relationship among algorithm, scheduling and architecture to describe the Inter process communication

Basically three types of model are there:

Precedence process model(DAG)

Directed edges represent the precedence relationship

Communication process model

In this model processes co-exist and Communicate synchronously.

Edges in this model represent the need of communication between the processes

Disjoint process model:

In this processes run independently and completed in finite time.

Processes are mapped to the processors to maximize the utilization of processes and minimize the turnaround time of the processes.

N- Number of processes- Efficiency Loss when implemented on a real machine.RC-relative concurrencyRP-relative processing requirement

Speed up depends on: Design and efficiency of the scheduling algorithm. Architecture of the system

Speed up

Static Process Scheduling

Is used to find optimal solution to the problem.

There are two extreme cases of work assignment.

mapping of processes is done before execution of the processes. once process started it stays at the processor until completion of the process. And never preempted.

Decentralized and non –Adaptive are the drawbacks of Static process scheduling.

Dynamic load sharing and Balancing

Load balancing can be defined as a technique to distribute work between many computers processes or any other resources to get optimal resource utilization.

controller reduces the process idling through load sharing ie,by joining the shortest queue and equalizing queue sizes by load balancing.

Further, processes can be allowed to move from longer queue to shorter queue through load Redistribution.

Sender Initiated Algorithm

It is activated by a sender process that wishes to off-load some of its computation by migration of processes from a heavily loaded sender to a lightly loaded receiver.

Transfer of process form a sender to reciever requires three basic decisions.

Transfer policy:-when does the node become the sender?

Selection Policy:-How does the sender choose a process for transfer?

Location Policy:-which node should be the target reciever?

Receiver initiated Algorithm:-

This are the pull models in which receiver can pull a process from others to its site for execution.

They are more stable than the sender initiated algorithm.

At high system load ,process migrations are few and a sender can be found easily.

Receiver initiated algorithms perform better than the sender initiated algorithms

Both the algorithms can be combined depending on RT and ST.

Distributed process implementation

Remote Service:-The message is interpreted as a request for a known service at the remote site

Three different software levels:-As remote procedure calls at the language level.As remote commands at the operating system level.As interpretive messages at the application level.

Distributed process Implementation

Depending on how the request messages are interpreted, there are three main application scenarios:

Remote Service The message is interpreted as a request for a known service

at the remote site.

Remote Execution The messages contain a program to be executed at the

remote site.

Process Migration The messages represent a process being migrated to a

remote site for continuing the execution.

Remote Execution

The purpose of remote service is to access the remote host unlike remote service remote process maintains the view of originating system.

Some Implementation issues:-

load sharing algorithms.

Location independence.

System heterogeneity.

Protection and security.

Load-Sharing Algorithm

1.1. Each process server are responsible to maintain the load Each process server are responsible to maintain the load information.information.

2.2. The list of hosts participating are broadcasted.The list of hosts participating are broadcasted.

1.1. The selection procedure is by a centralized broker process.The selection procedure is by a centralized broker process.

2.2. Once a remote host is selected-Once a remote host is selected-

1.1. The client process server indicates the resource The client process server indicates the resource requirements to the process server at the remote site.requirements to the process server at the remote site.

2.2. If the client is authenticated and its resource If the client is authenticated and its resource requirements can be met, the server grants permission requirements can be met, the server grants permission for remote execution.for remote execution.

3.3. The transfer of code image follows, and the server The transfer of code image follows, and the server creates the remote process and the stub.creates the remote process and the stub.

4.4. The client initializes the process forked at the remote The client initializes the process forked at the remote site.site.

Location Independence

Process created by remote execution requires coordination to accomplish common task.

So it is necessary to support logical views for the processes.

Each remote process is represented by an agent process at the originating host.

It appears as though the process is running on a single machine.

System heterogeneity

If remote execution is invoked on heterogeneous host , then it is necessary to re-compile the program.

Overhead Issue.

Solution:Use canonical machine-independent

intermediate language for program execution.

Process Migration

The message represents a process being migrated to the remote site for continuing execution.

Process migration facility

State and context transfer:-It transfers the computation state information and communication state information

Real Time Scheduling:-

The systems which insures that certain actions are taken within specified time constraints are called real time systems.

Can be classified as: Static vs dynamic Premptive vs non-premptive Global vs Local

Rate Monotonic

It’s easy to implement.Sorts the tasks by the lengths of their

periods.It also makes very good priority

assignments.Rate monotonic is an optimal priority

assignment algorithm.

Deadline Monotonic:-In real time system some tasks need to complete execution a short time after being requested.

Earliest Deadline First:-this is applies dynamic priority scheduling to achieve better CPU utilization .

Real time Synchronization:-A set of tasks that cooperate to achieve a goal will need to share information and resources or other words synchronize with other tasks.

References:-

[1].http://en.wikipedia.org/wiki/

[2]. Randy Chow, Theodore Johnson, “Distributed Operating Systems & Algorithms”, Addison Wesley.(all diagrams)

[3].Dejan S. Milojicic Fred Douglis Yves Paindaveine Richard Wheeler Songnian Zhou, “Process Migration” , ACM Computing Surveys (CSUR) Volume 32 ,  Issue 3  (September 2000)

[4]. S. Cheng, J.A. Stankovic and K. Ramamritham, ‘‘Scheduling Algorithms for Hard Real-Time Systems: A Brief Survey’’, page6-7 in Hard Real-Time Systems: Tutorial, IEEE (1988).

[5] .Distributed Process Scheduling. Advanced Operating Systems Louisiana State University Rajgopal Kannan. Issues in Distributed Scheduling .www.csc.lsu.edu/

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