processscheduling

8/18/2019 ProcessScheduling

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Chapter 9Uniprocessor Scheduling

Operating Systems:

Internals and Design Principles, 6/E

William Stallings

Patricia Roy

Manatee Community College, Venice, FL

©!!", Prentice #all


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$im o% Scheduling

& $ssign processes to 'e e(ecuted 'y the

processor)s*

&Response time

& +hroughput

& Processor e%%iciency


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+ypes o% Scheduling


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Scheduling and Process State

+ransitions


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Leels o% Scheduling


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Long-+erm Scheduling

& .etermines /hich programs are admitted

to the system %or processing

&Controls the degree o% multiprogramming& More processes, smaller percentage o%

time each process is e(ecuted


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Medium-+erm Scheduling

& Part o% the s/apping %unction

& 0ased on the need to manage the degree

o% multiprogramming


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Short-+erm Scheduling

& 1no/n as the dispatcher

& 2(ecutes most %re3uently

& 4no5ed /hen an eent occurs 6 Cloc5 interrupts

6 478 interrupts

6 8perating system calls 6 Signals


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Short-+erm Scheduling Criteria

& User-oriented

6 Response +ime

& 2lapsed time 'et/een the su'mission o% a re3uest

until there is output

& System-oriented

6 2%%ectie and e%%icient utili:ation o% the

processor


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Short-+erm Scheduling Criteria

& Per%ormance-related

6 ;uantitatie

6 Measura'le such as response time and

throughput


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Scheduling Criteria


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Scheduling Criteria


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;ueuing .iagram


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Priorities

& Scheduler /ill al/ays choose a process o%

higher priority oer one o% lo/er priority

& Use multiple ready 3ueues to

representmultiiple leels o% priority

& Lo/er-priority may su%%er staration

6 $llo/ a process to change its priority 'ased

on its age or e(ecution history


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Priority ;ueuing


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.ecision Mode

&


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.ecision Mode

& Preemptie

6 Currently running process may 'e interrupted

and moed to the Ready state 'y the

operating system

6 $llo/s %or 'etter serice since any one

process cannot monopoli:e the processor %or

ery long


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Process Scheduling 2(ample


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First-Come-First-Sered

& 2ach process =oins the Ready 3ueue

& When the current process ceases to

e(ecute, the longest process in the Ready

3ueue is selected


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First-Come-First-Sered

& $ short process may hae to /ait a ery

long time 'e%ore it can e(ecute

& Faors CPU-'ound processes

6 478 processes hae to /ait until CPU-'ound

process completes


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Round Ro'in

& Uses preemption 'ased on a cloc5


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Round Ro'in

& Cloc5 interrupt is generated at periodic

interals

& When an interrupt occurs, the currently

running process is placed in the ready

3ueue

6


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2%%ect o% Si:e o% Preemption

+ime ;uantum


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2%%ect o% Si:e o% Preemption

+ime ;uantum


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;ueuing .iagram


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Shortest Process


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Shortest Process


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2(ponential Smoothing

Coe%%icients


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Use 8% 2(ponential $eraging


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Use 8% 2(ponential $eraging


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Shortest Remaining +ime

& Preemptie ersion o% shortest process

ne(t policy

& Must estimate processing time


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#ighest Response Ratio


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Feed'ac5

& Penali:e =o's that hae 'een running

longer

& .on>t 5no/ remaining time process needs

to e(ecute


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Feed'ac5 Scheduling


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Scheduling Policies


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Scheduling Policies


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Comparison o% Scheduling

Policies


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Formulas


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Simulation Result %or Waiting

+ime


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Fair-Share Scheduling

& User>s application runs as a collection o%

processes )threads*

& User is concerned a'out the per%ormance

o% the application

&


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Fair-Share Scheduler


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+raditional U


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0ands

& .ecreasing order o% priority

6 S/apper

6 0loc5 478 deice control

6 File manipulation

6 Character 478 deice control

6 User processes

2 l % + diti l U


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2(ample o% +raditional U

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