Summary : Distributed Process Scheduling

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Summary - Distributed Process Scheduling

• Prepared BY-
• JAYA KALIDINDI

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Summary of chapter 5

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

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A system performance model2

• 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

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Communication process model

• In this model processes co-exist and
  Communicate synchronously.
• Edges in this model represent the need of
  communication between the processes

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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.

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Speed up

• N- Number of processes
• ?- Efficiency Loss when implemented on a real
  machine.
• RC-relative concurrency
• RP-relative processing requirement
• Speed up depends on
• Design and efficiency of the scheduling
  algorithm.
• Architecture of the system

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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.

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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.

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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?

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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.

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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.

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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.

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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.

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Load-Sharing Algorithm

• Each process server are responsible to maintain
  the load information.
• The list of hosts participating are broadcasted.
• The selection procedure is by a centralized
  broker process.
• Once a remote host is selected-
• The client process server indicates the resource
  requirements to the process server at the remote
  site.
• If the client is authenticated and its resource
  requirements can be met, the server grants
  permission for remote execution.
• The transfer of code image follows, and the
  server creates the remote process and the stub.
• The client initializes the process forked at the
  remote site.

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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.

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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.

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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

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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

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Rate Monotonic

• Its 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.

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• 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.

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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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