real time and fault tolerance

7/25/2019 Real Time and Fault Tolerance

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UNIT 1STRUCTURE OF REAL TIMESYSTEM

Performance Measure of Real

time System

Task Assignments

Fault Tolerant Scheduling

Real Time Vs General purpose

Data Bases

Data Bases for ard Real Time

System

Real Time "ommunicationRoll No: 15


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Real Time System

It is one that must proess in!ormation

"ro#ue a response $ithin a spei%e# time

Fault TolerantE&:

Real'time OS are s)stems that respon#

to input imme#iatel)*The) are use# !or suh tas+s as na,i&ation-

.e%nition

Real Time an# Fault Tolerane


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Real Time System

Comman# an# ontrol s)stems-

proess ontrol s)stems-

/i&ht ontrol s)stems-spae station-

spae'0ase# #e!ense s)stems


Eample


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Other eamples o! real'time s)stems inlu#e:

omputer &ames

tra2 li&ht ontrol

proess ontrol in !atories 3e*&* hemial plants-!oo# pro#ution4

/oo# $arnin&

autopilots in airra!t


Eample


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Real time an also re!er to e,ents simulate# 0) a

omputer at the same spee# that the) $oul# our in

real li!e*

In &raphis animation-

!or eample- a real'time pro&ram $oul#

#ispla) o0ets mo,in& aross the sreen at the same

spee# that the) $oul# atuall) mo,e*



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For #esi&nin& a real'time s)stem- $e nee#:

6 Spei%ation lan&ua&es 7 per!ormane measures

8 that are apa0le o! epressin& timin& re9uirements

6 Means 0) $hih

8 To pre#it the eeution times o! pro&rams 3tas+- o0-

proess4

8 To mo#el the relia0ilit) o! so!t$are an# har#$are

8 To assi&n tas+s to proessors an# she#ule them

8 ) $hih the s)stem an 9ui+l) reo,er

!rom the !ailure o! an in#i,i#ual omponent



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Types #f Real Time System

;ar# Real'Time S)stems

Missin& a #ea#line an ause a si&ni%ant loss to

the appliation*

Eamples: Fl)'0)'$ire- po$er'plant*

So!t Real'Time S)stems

Missin& a #ea#line auses the 9ualit) o! ser,ie to

#e&ra#e- 0ut nothin& terri0le happens

Eamples:


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ard VS Soft Real Time system

som0o#)=&mail*om


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Performance Measure of Real time System

Real time s)stem use# !or ritial appliations


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S)stem A an# ha,e s)stem response times $ith the

pro0a0ilit) #ensit) !untions sho$n in %& 0elo$*

S)stem A is more pre#ia0le than s)stem an# sli&htl)

slo$er

Eample>



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Properties of Performance Measures

?oo# "er!ormane measure must:

som0o#)=&mail*om

1* Represent an e2ient eno#in& o! rele,ant

in!ormation

@* "ro,i#e an o0eti,e 0asis !or the ran+in& o! an#i#ate

ontrollers !or a &i,en appliation*

* "ro,i#e o0eti,e optimiBation riteria !or #esi&n

* Represent ,eri%a0le !ats*


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Traditional Performance Measures

Relia0ilit)

A,aila0ilit)

Throu&hput

Capait) Relia0ilit)

Follo$in&:



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Performa$ility

Impro,es tra#itional measures 0)

1* Epliitl)

@* Formall) aountin& !or the !at the per!ormane o! a

real time omputer shoul# tie# to the onse9uent

per!ormane o! the proess that it ontrols*

* Controlle# proess

* "er!orma0ilit) o! the real time omputer is #e%ne# as

the pro0a0ilit) that the omputer s)stem $ill allo$

eah aomplishment le,el to 0e met*



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ierarchical Vie% of Performa$ility

Impro,es tra#itional measures 0)



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Eah ,ie$ is #ri,en 0) the re9uirements o! the one

a0o,e it an# reei,es input !rom the one 0elo$ it*

Eah ,ie$ is more #etaile# than the one a0o,e it*

"er!orma0ilit) ta+es the operatin& en,ironment into

aount in


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Dualities o! "er!orma0ilit):

6


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&ST'MAT'(G PR#GRAM R)( T'M&S

Soure o#e: Soure o#e that is are!ull) tune# an#

optimiBe# ta+es less time to eeute*

Compiler:The ompiler maps the soure'le,el o#e into

a mahine'le,el pro&ram* The eeution time $ill

#epen# on the nature o! the mappin&*

Mahine arhiteture: Man) aspets o! the mahine

arhiteture ha,e an eGet on the eeution time that

is #i2ult to 9uanti!) eatl)*

Operatin& s)stem

.epen#s on the !ollo$in& !ators:



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Task Times*

6 Response time:

8 Time 0et$een tas+ release# to atual #eli,ere#

6 Dueue time:

8 At 0uGer

6 En#'to'en# #ela):

8 .ela) o! appliations

6 "athHeeution #ela):



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'deal Tool



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Task Assignment

The purpose o! real'time omputin& is to eeute-

0) the appropriate #ea#lines- its ritial ontrol

tas+s*

Alloatin& an# she#ulin& tas+s on proessors

Inlu#es



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"ontinue

The alloationHshe#ulin& pro0lem an 0e state# as

!ollo$s*

?i,en a set o! tas+s

Tas+ pree#ene onstraints

Resoure re9uirements

Tas+ harateristis

.ea#lines*



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)niprocessor Task Scheduling

Eah tas+ is perio#i

"erio#s o! #iGerent tas+s ma) 0e #iGerent

orst'ase tas+ eeution times are +no$n

Relati,e #ea#line o! a tas+ is e9ual to its perio#

No #epen#enies 0et$een tas+s: the) are in#epen#ent

Onl) resoure onstraint onsi#ere# is eeution time

No ritial setions

"reemption osts are ne&li&i0le

Tas+s must 0e omplete# !or output to ha,e an) ,alue

Initial Assumptions:



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Standard Scheduling Algorithms

Rate'Monotoni 3RM4 Al&orithm:

Stati priorit)

;i&her'!re9uen) tas+s ha,e hi&her priorit)

Earliest'.ea#line First 3E.F4 Al&orithm:

.)nami priorit)

Tas+ $ith the earliest a0solute#ea#line has

hi&hest priorit)

Inlu#es



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Fault Tolerant Scheduling

Fault'tolerane is the a0ilit) o! a s)stem to maintain its

!untionalit)- e,en in the presene o! !aults*

The three 0asi notions are fault- failure- an# error:

The !ollo$in& ausal relationship:

'' !ault '' error '' !ailure '' !ault '' ***

Intro#ution



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Fault'tolerant she#ulin&

Shoul# 0e a0le to run one or more opies o! eah

,ersion o! a tas+ #espite the !ailure o! up to n

proessor

The approah ta+en: &host opies o! tas+s

Em0e##e# into the she#ule

Nee# not to i#ential to the primar) opies



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Real Time


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A0solute onsisten) is aura)* The #ata returne# in response to

a 9uer) must 0e lose to the results epete#*

Relati,e onsisten) means that !or multiple #ata- the #ata must

ha,e 0een ollete# reasona0l) lose to one another*

A$solute Vs Relati+e "onsistency



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(eed for Response Time predicta$ility

There are man) !ators that aGet the response time

pre#ita0ilit)

The re9uirement to meet the ACI. properties $illentail a o,erhea#*

.ata0ases are o!ten 9uite lar&e to %t in the mainmemor) an# there!ore rel) mainl) on the #is+ 0ase#s)stems*

Transation aess are #ata #epen#ant* Thetransation to #e#ut an amount !rom a #ata0ase$hih has lo$er 0alane is !aster $hereas the hi&her0alane lea#s to slo$ness*

Transation ma) suGer $ith a #ela) in aessin& aReal Time an# Fault Tolerane


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Data Bases for ard Real Time System

.isa#,anta&es o! lient ser,er: time onsumin& .ata0ases !or real time s)stems are meant !or the use o!

0oth har# an# so!t s)stems*

Sine har# real time s)stems nee#s strit timin&

onstraints- on,entional #is+ 0ase# #ata0ases are notsuita0le

ut so!t real time s)stems ma+es use o! #is+ 0ase#

s)stems throu&h FCFS* There shoul# 0e some solution !or ;ar# Real time

s)stems $ith hi&h per!ormane an# &uarantee# responsetime onstraints*

M.ARTS 3Multiproessor .ata0ase Arhiteture !or RealReal Time an# Fault Tolerane


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It is a main memor) #ata0ase 3the entire #ata0ase resi#es on themain memor)4

O0et oriente# #ata0ase 3CJJ elements4

Supports epliit #elaration o! real time onstraints an# semanti

onstraints $ithin the appliation o#e*

The a0o,e are the onstraints $hih an 0e inlu#e# in theappliation o#e #iretl) $ithout the reompilation o! the M.ARTS

li0rar)*

Supports #iret- onurrent- share# memor) #ata aess*

Features



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Real'time ommuniations

Real'time ommuniations 3RTC4 is an) mo#eo! teleommuniation in $hih all users an ehan&ein!ormation *

Teleommuniations that our $ithout transmission#ela)s*

RTC is nearl) instant $ith minimal laten)*

RTC #ata an# messa&es are not store# 0et$eentransmission an# reeption*

RTC is &enerall) a peer'to'peer- rather than

0roa#astin& or multiastin&- transmission*

Conept



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Communiation Me#ia T)pes



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RTC #ata transmission mo#es are as !ollo$s:

;al! .uple:

Ours 0i#iretional - 0ut not simultaneousl)on a sin&le arrier or iruit

Full .uple:

Ours 0i#iretional an# simultaneousl) on a sin&learrier or iruit

Transmission Mo#es



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Internet

Lan# lines Mo0ileHell phones

instant messa&in& 3IM4

Internet rela) hat


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Eamples o! RTC inlu#e



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TA(, -#)

real time and fault tolerance

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