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Introduction to Solaris

Developed in 1987 by AT&T and Sun Microsystems

!ompatible "it# SPA$! arc#itecture

%penSolaris "as t#e %pen Source version o t#e Solaris operating system"#ic# #as been discontinued ater %racle too' over in ()1)

%S amily* +ni,

Programmed in * ! Deault +I* -.%M/

Mi,ed Source0 %nly certain eatures are open source

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Process

T#e most basic abstraction provided by an %perating System

A process is an e,ecutable obect located at p#ysical memory pages

/very process #as its o"n uni2ue integer number called Process ID

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Solaris 3ernel T#reads

A thread is an independent lo" o control t#at operates "it#in t#e sameaddress space as ot#er independent lo"s o control "it#in a process

Solaris is a multi0t#read %perating System4 t#at is every tas' perormed ise,ecuted li'e a 'ernel t#read

%n a single processor4 multit#reading is generally implemented by time0division multiple,ing 5as in multitas'ing6* t#e processor s"itc#es bet"een

dierent t#reads T#is conte,t s"itc#ing generally #appens re2uently enoug#t#at t#e user perceives t#e t#reads or tas's as running at t#e same time

%n a multiprocessor or multi0core system4 t#reads can be truly concurrent4"it# every processor or core e,ecuting a separate t#read simultaneously

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Advantages o T#reads in Solaris

T#e main beneit o t#reads 5as compared to multiple processes6 is t#at t#econte,t s"itc#es are muc# c#eaper t#an t#ose re2uired to c#ange current

processes

/ven "it#in a single0processor environment4 multiple t#reads are

advantageous because one t#read may be able to progress even t#oug#anot#er t#read is bloc'ed "#ile "aiting or a resource

T#reads also #ave private resources 5program counter4 stac'4 register conte,t4etc6

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ig#t"eig#t Processes

A lig#t"eig#t process can be considered as t#e s"appable portion o a 'ernelt#read A lig#t0"eig#t process 5P6 is a means o ac#ieving multitas'ing

A P runs in user space on top o a single 'ernel t#read and s#ares itsaddress space and system resources "it# ot#er Ps "it#in t#e same process

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ombie Processes

 #en a process dies4 it becomes a :ombie process A :ombie process ordeunct process is a process t#at #as completed e,ecution but still #as an

entry in t#e process table

.ormally4 t#e parent perorms a "ait56 and cleans up t#e PID

3illing t#e parent or rebooting "ill also clean up :ombies

T#e correct ans"er is to i, t#e buggy parent code t#at ailed to perorm t#e"ait56 properly

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Managing System Processes

ps0 c#ec's status o all active processes T#e ollo"ing inormation is reported "#en tcommand is e,ecuted

!urrent status o t#e process

Process ID

Parent process ID

+ser ID

Sc#eduling class

Priority

Address o t#e process

Memory used

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pldd0 ists t#e dynamic libraries t#at are lin'ed into a process

pmap0 Prints t#e address space map o eac# process

pstop0 stops t#e process

p"d,0 Displays t#e current "or'ing directory or a process

ptree0 Displays t#e process trees t#at contain t#e process

p'ill0 To 'ill a process in case it gets stuc' in an ininite loop

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Process Scheduling0Priority Model

T#e Solaris 'ernel is ully preemptible T#is means t#at all t#reads4

including t#e t#reads t#at support t#e 'ernel;s o"n activities4 can be

deerred to allo" a #ig#er0 priority t#read to run

 Solaris recogni:es 17) dierent priorities4 )01

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Sc#eduling classes in Solaris

TS (timeshare): T#is is t#e deault class or processes and t#eirassociated 'ernel t#reads Priorities "it#in t#is class range )0>94 and

are dynamically adusted in an attempt to allocate processor

resources evenly

IA (interactive): T#is is an en#anced version o t#e TS class t#atapplies to t#e in0ocus "indo" in t#e -+I Its intent is to give e,tra

resources to processes associated "it# t#at speciic "indo" i'e TS4IA;s range is )0>9

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FSS (fair-share scheduler): T#is class is s#are0based rat#er t#anpriority0 based T#reads managed by ?SS are sc#eduled based on t#eir

associated s#ares and t#e processor;s utili:ation ?SS also #as a range

)0>9

FX (fixed-priorit): T#e priorities or t#reads associated "it# t#isclass are i,ed 5In ot#er "ords4 t#ey do not vary dynamically over t#e

lietime o t#e t#read6 ?@ also #as a range )0>9

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S!S (sstem): T#e SS class is used to sc#edule 'ernel t#readsT#reads in t#is class are BboundB t#reads4 "#ic# means t#at t#ey run

until t#ey bloc' or complete Priorities or SS t#reads are in t#e 94 so an $T t#read "ill

preempt a system t#read $eal time processes cannot be preemptedby any ot#er process4 t#ereore it usually re2uires administrative

privileges to run It is normally not advisable to create a $T process

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Implementation o Time Slicing or TS

and IA

TS and IA sc#eduling classes implement an adaptive time slicing

sc#eme t#at increases t#e priority o I=%0bound processes at t#e

e,pense o compute0bound processes T#e e,act values t#at are used

to implement t#is can be ound in t#e dispatc# table

To e,amine t#e TS dispatc# table4 run t#e command

dispadmin 0c TS 0g

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T#e ollo"ing values are reported in t#e dispatc# table*

ts#$uantum* T#is is t#e deault lengt# o time assigned to a process "it# t#especiied priority

ts#t$exp* T#is is t#e ne" priority t#at is assigned to a process t#at uses itsentire time 2uantum

ts#slpret* T#e ne" priority assigned to a process t#at bloc's beore using its

entire time 2uantum

ts#max%ait* I a t#read does not receive !P+ time during a time interval otsCma,"ait4 its priority is raised to tsCl"ait

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Modiying t#e dispatc# table

dispadmin can be used to edit t#e dispatc# table to aect t#e decay opriority or compute0bound processes or t#e gro"t# in priority or I=%0bound

processes

 In particular4 tsCma,"ait and tsCl"ait can prevent !P+ starvation4 and

raising tsCt2e,p slig#tly can slo" t#e decline in priority o !P+0boundprocesses

In any case4 t#e dispatc# tables s#ould only be altered slig#tly at eac# step int#e tuning process4 and s#ould only be altered at all i you #ave a speciic

goal in mind

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Time Slicing or ?SS

In ?SS4 t#e time 2uantum is t#e lengt# o time t#at a t#read is allo"ed to runbeore it #as to release t#e processor T#is can be c#ec'ed using

dispadmin 0c ?SS 0g

 T#e +A.T+M is reported in ms 5T#e output o t#e above command displayst#e resolution in t#e $/S parameter T#e deault is 1))) slices per second6 It

can be adusted using dispadmin as "ell

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T#undering Eerd

#en a resource is reed4 all t#reads a"aiting t#at resource are

"o'en T#is results in a ootrace to obtain access to t#at obectF one

succeeds and t#e ot#ers return to sleep5bloc'ed state6 T#is can lead

to "asted over#ead or conte,t s"itc#es T#is is called a Bt#undering

#erdB problem

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Issues "it# $eal Time processes

$eal time processes also loc' all t#eir pages in memory T#is can causeproblems on a system t#at is underconigured or t#e amount o memory t#at

is re2uired

 Since real time processes run at suc# a #ig# priority4 system daemons maysuer i t#e real time process does not permit t#em to run

 #en a real time process or's4 t#e ne" process also in#erits real time

privileges T#e programmer must ta'e care to prevent unintendedconse2uences oops can also be #ard to stop4 so t#e programmer also needs

to ma'e sure t#at t#e program does not get caug#t in an ininite loop

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$eerences

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