operating systems - cs604 power point slides lecture 18

7/25/2019 Operating Systems - CS604 Power Point Slides Lecture 18

1/30

perating

Systems

Lecture 18

Syed Mansoor Sarwar


2/30

January 27, 2016 Copyright Virtua !ni"ersity o# $a%istan

Agenda for Today

&e"iew o# pre"ious ecture

!'() Syste* V scheduing

+gorith* e"auation

$rocess synchroniation

&ecap o# ecture


3/30


4/30


"ery second, the priority nu*/er o# a

those processes that are in the *ain

*e*ory and ready to run is updated /yusing the #oowing #or*ua

Priority# = (RecentCPU Usage)/2 + Thr. Pri.+ nice

hreshod priority and nice "aues areaways positi"e to pre"ent a user #ro*

*igrating out o# its assigned group

UNIX System

Sc!edu"ing A"gorit!m


5/30


i*e

0

1

2

3

4

5

$riority

60

75

67

63

76

68

C$!Count

0160

30

30

1

!"6!33

16

$+

$riority

60

60

75

67

63

76

C$!Count

0

0

1

60

30

30

1

!"6!

33

$

$riority

60

60

60

75

67

63

C$!Count

0

0

01

60

30

30

1

!

$C

UNIX System #$amp"e


6/30


Round Ro%in Sc!edu"ing

and &rocess &riorities

+

7ig

her$riority

60

+

+

+

+ + runs #irst

1

4

2 3

5 6


7/30


A"gorit!m #va"uation

+naytic "auationhe agorith* and so*e syste*

wor%oad are used to produce a

#or*ua or nu*/er which gi"es theper#or*ance o# the agorith* #or that

wor%oad

9eter*inistic *odeing

:ueuing *odes

(*pe*entation


8/30


'eterministic (ode"ing

$redeter*ined wor%oad andper#or*ance o# each agorith* #or

that wor%oad !se o# ;antt charts

Si*pe and #ast


9/30


$rocess +rri"a i*e urst i*eP

1 00 7

P2

20 4

P3 40 1

P4

50 4

;antt chart

+"erage waiting ti*e = >? @ 1 @ 0 @2AB4 = 3

P3

P2

42 110

P4

5 7

P2

P1

16

P1

'eterministic (ode"ing


10/30


)ueuing (ode"ing

Co*puter syste* "iewed as anetwor% o# .ueues and ser"ersready .ueue, (B .ueue, e"ent

.ueues, C$!s, (B de"icecontroers, etc

n$%t&+rri"a and ser"ice rates

'%t$%t&C$! utiiation, a"erage

.ueue ength, a"erage

waiting ti*e, D


11/30


)ueuing (ode"ing

itte*s or,%an = EF G

wheren= a"erage .ueue ength

-= a"erage arri"a rate

= a"erage waiting ti*e in a

.ueue


12/30


)ueuing (ode"ing

Let the a"erage Ho/ arri"a rate /e 05+gorith* +"erage Gait

i*e

G=tw

+"erage :ueueLength>nA

ICIS 46 23

SJI 36 18

S&I 32 16

&& >.=1A 70 35

&& >.=4A 60 30


13/30


)ueuing (ode"ing

Co*picated *athe*atics9istri/utions >$oisson, uni#or*,

e


14/30


Simu"ation

$rogra**ing *ode #or theco*puter syste*

Gor%oad generated /yassu*ing so*e distri/ution and

a rando* nu*/er generator, or

/y coecting data #ro* the

actua syste*


15/30


Simu"ation

Characteristics


16/30


Simu"ation


17/30


Imp"ementation

est

Most e


18/30


&rocess

Sync!roni*ationConcurrent access to shared

data *ay resut in data

inconsistencyMaintaining data consistency

re.uires *echanis*s to ensurethat cooperating processesaccess shared data

se.uentiay


19/30


+ounded,+uffer &ro%"em

hare atade#ine !II&KS( 10

typede# struct

N ite*O

ite* /u##erP!II&KS(QOint in= 0, o%t= 0O

int co%nter= 0O


20/30


Pro%cer $rocessite* ne1A whie >counter == !II&KS(A O

/u##erPinQ = nein @ 1A R !II&KS(O

counter@@ON



21/30


ite* ne1A

whie >counter == 0A O

neout @ 1A R !II&KS(O counter--O

N


Cons%,er $rocess


22/30


counter++T in asse*/y anguage

' R1 co%nter

4C R1

' co%nter R1

counter--T in asse*/y anguage' R2 co%nter

5C R2



23/30


(# /oth the producer and consu*eratte*pt to update the /u##er

concurrenty, the *achine anguage

state*ents *ay get interea"ed

(nterea"ing depends upon how the

producer and consu*er processes

are schedued



24/30


7ss%,e counteris initiay . 'neinterea8ing o9 state,ents is&

$ro%cer& ' R1 co%nter (R1 = ) 4C R1 (R1 = 6)cons%,er& ' R2 co%nter (R2 = ) 5C R2 (R2 = :)$ro%cer& ' co%nter R1 (co%nter = 6)

cons%,er&' co%nter R2 (co%nter = :)

The 8a%e o9 co%nt ,ay ;e either : or 6


25/30


Race Conition he situation

where se"era processes access

and *anipuate shared data

concurrenty, the #ina "aue o# the

data depends on which process#inishes ast

&rocess

Sync!roni*ation


26/30


Critica ection + piece o# code

in a cooperating process in which

the process *ay updates shareddata >"aria/e, #ie, data/ase, etcA

Critica ection Pro;e,Seriaie e


27/30


o9t


28/30


o >

critica section

re,iner section

?


29/30


Recap of Lecture

!'() Syste* V scheduing

+gorith* e"auation

$rocess synchroniation

&ecap o# ecture


30/30

perating

Systems

Lecture 18

Syed Mansoor Sarwar

operating systems - cs604 power point slides lecture 18

Documents