Lecture 1: Course Overviewcseweb.ucsd.edu/classes/su09/cse120/lectures/Lecture1.pdf · Recap: Role...

Lecture1:CourseOverviewCSE120:PrinciplesofOpera;ngSystems

UCSanDiego:SummerSessionI,2009FrankUyeda

GoalsforToday

•  Introduc;ontocourse:–  Personnel,policiesandadministra;on

•  Providehigh‐leveloverviewofcoursematerial–  Specificgoals

•  Defineanopera;ngsystem–  Iden;fyitsrole

•  Iden;fythehardwaremechanismsavailabletotheOpera;ngSystem

•  Note:someslidecontentandimagesareadaptedfromAlvinAuYoung,GeoffVoelker,AlexSnoeren(UCSanDiego)andAnthonyJoseph(UCBerkeley)

Lecture1:Courseoverview

WhoamI?

•  PhDcandidateinCSEdepartment–  UCSDundergrad(Warrencollege)andUCSDgraduatestudent

– WorkingwithProfessorGeorgeVarghese&AminVahdatinSystemsandNetworkinggroup

–  Conductresearchandpublishpapersinarea

•  Iamfascinatedbythistopic,andwouldliketosharemyexcitementforitwithyou.


BasicInforma;on

•  Instructor:FrankUyeda–  E‐mail:[email protected]–  OfficeHours:Tues2‐4p,CSE2126

•  Orbyappointment

•  TA:MatusTelgarsky–  E‐mail:[email protected]–  OfficeHours:Wed?

•  Mee;ng;mes:–  Lecture:MWF,4p‐5:50p,Center201–  Discussion:Thursday@??–  FinalExam:Saturday,August1,3pm


DiscussionSec;on

•  Survey:Whenwouldyouliketohavediscussionsec;on?– Thursday11a–12p– Thursday12p–1p– Thursday1p–2p


PurposeofthisCourse

•  Goalistohelpyouunderstandstructureanddesignofmodernopera;ngsystems:–  Lecturesandreadingstodis;llinforma;on–  Homeworksetsandprogrammingprojectstoreinforceideas

•  Attheendofthecourseyoushouldbeableto:–  Iden;fycommondesignchallengesforanOS–  Understandtradi;onalmechanismsandpoliciesusedtoaddressthesechallenges

–  Hypothesizehowchangesintechnologywillimpactexis;ngOSmechanismsorpolicies


Prerequisites

•  Courses–  CSE100(DataStructures),CSE101(Algorithms)required

–  CSE141(notrequiredbutuseful)•  Programming–  Java‐basedprojects.CSE100shouldbeadequate.

•  Hoursperweek–  Studentsaveraged12hours/weekinregularterm(CAPEevalua;ons)

–  ≈24hours/weekinsummer?


Homework

•  Purpose–  Reinforceconceptsthroughprac;ce(therearechallengingconceptsinthisclass)

•  Threehomeworkassignments–  AssignmentsdueonMonday’satthebeginningofclass.

–  Nolateassignments–  Collabora;onencouraged,butmustbecompletedindividually

–  Allanswersmustbelegible–ifwecan’treadit,youdon’tgetcredit.


PeerWise

•  Submitpoten;altestques;onsandanswers.•  Readandrateques;onssubmikedbyothers.•  hkp://peerwise.cs.auckland.ac.nz/

•  Assignment:–  Submit1ques;onandreview10others.–  DueeveryTuesdayandThursday@11:59pm.

•  Iwillshowsomeofthebest/worstques;onsinclass.•  Atleastoneques;onsubmikedthroughPeerWisewillshowupontheFinal!


Projects

•  Purpose– Hands‐onexperience:implemen;ngismuchtrickierthandiscussingconcepts.

•  Nachos–  Instruc;onal‐basedOpera;ngSystemdevelopedatUCBerkeley(TomAnderson),runningonmachinesimulator

–  You’llexpandNachosin3projectcomponents.–  Significantpor;onofcourse(very;meconsuming)– Nolateassignmentsaccepted(3slipdaysallowed)


Projects(2)

•  Roughoutline:–  Project1:Concurrencyandsynchroniza;on–  Project2:Mul;programming–  Project3:VirtualMemory

•  Groups–  Projectsmaybedoneonyourownorwithapartner.–  Youwillhavethesamepartnerforthewholecourse.

–  Pleaseiden;fyyourpartnerearlyandno;fymeviaemail.


Exams

•  Midterm–  Date:Wednesday,7/17/09,4p‐5:20p

–  Loca;on:Center201

•  Final–  Date:Saturday,8/01/08,3p‐6p–  Loca;on:Center201

•  Make‐uppolicy–  Onlyunderextreme,university‐approvedcircumstances


ClassResources

•  ClassWebpage–  hkp://www.cs.ucsd.edu/classes/su09/cse120–  announcementsandscheduleupdates

•  Messageboard–  hkp://webct.ucsd.edu–  Forumtodiscussissuerelatedtotheprojects.

•  Textbooks–  (Required)Silberschatz,GalvinandGagne,Opera&ngSystemsConcepts,7thedi;on,WileyandSons•  Bookstorecurrentlycarriesthe8thedi;on(thisisfine,too).

–  (Op;onal)Tanenbaum,ModernOpera&ngSystems,3rdedi;on,Pren;ceHall


ClassResources(2)

•  Labs–  YoushouldhaveaccesstoaLinuxaccountandlabmachinesinbasementofEBU3B

•  Youarefreetoworkfromhome–  NachosworksonEclipse/Windows– WewillgradeonLinuxmachines,somakesurecoderunsonlabmachinesaswell


Grading

•  Homeworkassignments(15%)•  PeerWisepar;cipa;on(5%)•  Programmingprojects(30%)•  Midtermexam(20%)•  Finalexam(30%)

•  Gradeswillassignedonastraightscale:– A:>90;B:>80;C:>70;etc…–  +’sand–’sgivenatthediscre;onofinstructor


CommonCSE120Pitalls

•  Don’tspend;meonthehomework–  It’sonly15%ofmygrade

–  Conceptsmayseemeasy,butactuallyrequiresignificantprac;cetofullyunderstand

– Masteryofconceptscomeinhandyforprojectsandexams

•  Putofftheproject–  I’vegotbe=erthingstodo,ormypartnerwilldoit–  Hardlyanybodyfinishesthemearly–tes;ngalonewillrequiresignificant;me

–  Project‐relatedques;onsmayendupontheexam


CommonCSE120Pitalls(2)

•  Don’taskques;ons–  Idon’twanttolookstupid– MatusandIareheretohelp–  Chancesaremanyotherpeoplehavethesameques;on

–  Puungoffques;onswilljustcreatemoreques;ons


ModernComputerSystems


Telema;cssystems

Cellphonesandhandhelddevices

Gamingconsoles

Sensornodes

Routers

ComputerOrganiza;on


CPUVideo

controllerUSB

controllerDisk

controller

Memory

MonitorScanner

Keyboard

Printer

Diskdrive

WhatistheOpera;ngSystem?

Systembus

WhatisanOpera;ngSystem?


Applica;ons

Opera;ngSystems

Hardware

)

VM

TheOSis“allthecodeyoudidn’thavetowrite”toimplementyourapplica;ons.

WhatisanOpera;ngSystem?


Applica;ons

Opera;ngSystems

Hardware

Games(CSE125)Compilers(CSE130,131)Databases(CSE132A,B)WebApps(CSE134A,B)…

PrinciplesofOpera5ngSystems(CSE120)AdvancedOpera;ngSystems(CSE121))

Architecture(CSE141/L)DigitalSystems(CSE140/L)

TheOSis“theprogramthatisalwaysrunning”.

WhyStudyOpera;ngSystems?

•  Understandwhatyouuse– Whichopera;ngsystemisrightforme?– MycomputerisslowandI’mnotsurewhy!–  AmIprotectedagainstworms,viruses,andothersecurityvulnerabili;es?

•  Learnthepastbeforeyoucreatethefuture–  Pervasiveabstrac;ons(e.g.,threadsandsynchroniza;on)–  Evolu;onofOSeshavefollowedadvancesintechnology

•  Developexperiencedevelopingcomplexsystem–  Largesystemwithmanymovingparts(HW,SW)– Manydesigngoals(efficiency,flexibility,security,…)


CourseContent

•  RoleofanOpera;ngSystem•  ConcurrencyandSynchroniza;on

– Whatarethechallengestosupportmul;tasking?•  CPUScheduling

– WhogetstheCPUandwhendotheygetit?•  MemoryManagement

–  Howdoprogramssharefinitememory?•  FileSystemsandStorageManagement

–  Howisdatastoredandwhathappenswhenthingsfail?•  Selec;onofSpecialTopics(;mepermiung)

–  Security,VirtualMachineMonitors,…..


Midterm

RoleofanOpera;ngSystem


Applica;ons

Opera;ngSystems

Hardware

)

VM

Provideabstrac;onstoeaseapplica;ondevelopment



Applica;ons

Hardware

VM

Provideabstrac;onstoeaseapplica;ondevelopment

1.Userinputdata

2.CPUcomputesnextframe

3.Renderimageonmonitor

•  Anapplica;onneedstobeabletotalktoeachdevice:– Whatifaresourceisbusy/fails?– Whatifthehardwarechanges?

•  Everyapplica;onwillbeextremelycomplex–  Redundant,error‐pronecode–  Notportable(hardwarelimita;ons)



Applica;ons

Opera;ngSystems

Hardware

)

VM

Managesresourceaccessamongapplica;ons

•  OSschedulesresourceaccess–  Significantperformanceimpact–  Flexiblesharingpolicies

•  OScanprovideprotec;onmechanisms–  Privacy(filepermissions)–  Flexiblepolicies(groups)

•  OScanprovidecoordina;onmechanisms–  Communica;on(pipes,cut+paste)–  Synchroniza;on(monitors,

semaphores)

Recap:RoleofanOpera;ngSystem

•  Provideabstrac;ons•  Manageresources•  Asaresult:

–  Hardtoproperlydefineboundaries–  OSesbecomingincreasinglycomplex

Breakfor5Minutes

•  WhatbelongsintheOpera;ngSystemvs.Applica;ons?– Getuserinputfromperipheraldevice

•  OS–centralmanagementfordevicedriversandcommoninterfaceexposedtouserprograms

– Setthesystem;me/date•  OS‐allotherprograms/userssharethisvalue.

– Renderawebpage•  Dependswhoyouask!


WhatIsn’tanOpera;ngSystem?

•  UnitedStatesvMicrosoz(2000)– MicrosozbundledIEwithWindows–  USDOJbringsan;‐trustcaseagainstMicrosoz

•  Outcome–  Basicques;on:isbrowserpartoftheOS?–  CSacademicstes;fied“no”–  Seklement

•  MicrosozmustshareAPIwiththird‐partycompanies

Difficulttodefineboundaries


0.00

10.00

20.00

30.00

40.00

50.00

60.00

WindowsNT3.1

WindowsNT3.5

WindowsNT3.51

WindowsNT4.0

Windows2000 WindowsXP WindowsServer

WindowsVistaBeta

1993 1994 1995 1996 1999 2001 2003 2006

Source:LarryO’Brien,knowing.net(2008)

SLOC(m

illions)

OSesbecomingincreasinglycomplex


0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

WindowsNT3.1

WindowsNT3.5

WindowsNT3.51

WindowsNT4.0

Windows2000

RedHatLinux6.2

Debian2.2WindowsXP

RedHatLinux7.1

WindowsServer

MacOSX WindowsVistaBeta

1993 1994 1995 1996 1999 2000 2000 2001 2001 2003 2005 2006

Sources: debian‐coun;ng,escet.urjc.es(2002),SteveJobsWWDCkeynote(2006)

SLOC(m

illions)

OSesbecomingincreasinglycomplex

HardwareSupport

•  Whydoweneedtodiscusshardware?–  KeygoaloftheOSistoprovideresourcesharing.– WithgoodOSdesign,applica;onscanbeoblivioustoHWdetails(abstrac;on).

–  TheOSstandsbetweentheHWandtheapplica;ons,soitmustconsidertherequirementsofboth.

HardwareSupport

•  Earlyprocessorsofferedlikleinthewayofprotec;on–  Aprocesscouldaccessanymemoryloca;on–  Aprocesscouldaccessanyhardwaredevice–  Couldimplementprotec;oninsozware,butreallyslow…

•  HardwarefeaturesevolvetomeetneedsofOS– Ex.TLB,Testandsetinstruc;on,Noexecutebit

TypesofHardwareSupport

•  Protec;on–  OSwantstocontrolhardwareaccess–  OSwantstokeeppar;culardata(registers,memory)privateandisolated

•  Eventhandling–  OSneedstobeawareofexternalevents–  OSneedsawaytorespondtoexternalevents

•  Performanceimprovements–  Commonlyusedthreadsynchroniza;onprimi;ves

– Memoryaccess/Diskaccessspeed‐ups

Laterinthecourse

Protec;on

•  Hardwarefeatures–  Protec;onlevels,privilegedinstruc;ons(CPU)–  VirtualMemory(MMU)

•  Whatdoweneedtoprotect?– Directaccesstopar;culardevices,suchasstoragedevices,orinput/outputperipherals.(why?)

– Memorystate,suchaspagetableentries,TLBentries–  Specialopera;ons,suchaschangingprotec;onlevel,interrupthandling,hal;ngthemachine

Markpar;cularinstruc;onsasprivileged

Suppor;ngPrivilegedInstruc;ons

•  Hardware(CPU)offersprotec;onlevels–  Processorsactuallyprovidemanylevels:x86architecture

supportsatleastfourmodes(“rings”)–  Linuxandmostopera;ngsystemsusetwomodes:userand

kernelmode

•  HowdoesanOSorCPUuseprotec;onlevels?–  ThereisaspecialregisterontheCPUindica;ngthemode–  CPUchecksmodebitwhenexecu;ngprivilegedinstruc;ons

– Userprogramsexecuteinusermode– OSexecutesinkernelmode

•  Fornow,thinkofthekernelasequivalenttoanOS

UserandKernelMode

•  Privilegedinstruc;onscanonlybeexecutedwhileinkernelmode– Whichinstruc;onsareprivileged?

•  Examplesofprivilegedinstruc;ons:– Manipula;ngmemorystate,directaccesstoHW

•  Examplesofnon‐privilegedinstruc;ons– Anythingthatcan’tbotherotherprograms/apps/processes

•  Whydon’twejustmakeeveryinstruc;onprivileged?

UnixOrganiza;on

UserMode

KernelMode

Hardware

Applica;ons

StandardLibs

Example:MemoryProtec;on

•  Remember:OSmustprotectprogramsfromeachotherandprotectitselffromprograms

•  We’vetalkedabouttheCPU,butwhataboutMemory?–  Containsalotofprogramstate– MemoryManagementUnit(MMU)providesprotec;on

•  Baseandlimitregisters,segments,pagetables,TLB,VirtualMemory

•  Manipula;onofthesestructuresareprotected

–  Thepar;cularsofthesestructureswillmakemoresensewhenwetalkaboutmemorymanagement

Events

•  Aneventisanunnaturalchangeincontrolflow–  Eventscanstoporchangecurrentexecu;onpath–  Eventscanchangemachinestate(protec;onlevel,registers,etc…)

•  Kerneldefinesahandlerforeacheventtype–  Eventhandlersruninkernelmode–  Eventsaretheonlyentryintothekernel

Events

•  Twotypesofevents–  Interrupts:causedbyexternalevent–  Excep;ons:causedbyaninstruc;on

•  Eventscanbe:–  Unexpected–  Deliberate


Unexpected Deliberate

Excep5on(sync) Fault Syscalltrap

Interrupt(async) Interrupt SozwareInterrupt

Interrupts

•  AsignalissenttotheOSonaphysicalwire(Interrupt‐requestline)

•  Hardwareinterrupts–  Generallytheseeventsareasynchronous–  e.g.,Networkpacketarrival,DMAcomple;on

•  Hardware/SozwareTimers–  Specialtypeofevent–  AllowOStoregaincontrol(why?)

HandlingInterrupts

•  Polling–  Kernelbusy‐waitsforsignal

•  Note:textbookusesslightlydifferentdefini;onanddis;nguishesitcompletelyfromIRQ

–  Canbeinefficientdependingonfrequency

•  InterruptHandler–  Interruptcausesprocessortotrapintokernel–  Kernelinvokesappropriateinterrupthandler–  Interrupthandlersavesprocessstate,processesinterrupt,restoresstateandreturns

IssueswithInterrupts

•  Whatifaninterruptoccurswhileinaninterrupthandler?–  Canmaskinterrupts(seeNachos)–  Interruptpriority(supportdifferentpolicies)

•  Whatcangowrong?–  Faultydriver

•  Ininterruptchaining,OSquerieseachdriver’sinterrupthandler•  Falseposi;vecancreatefloodofinterrupts

–  Badstate(LiveLock)•  Receiverlive‐lock:toomanypacketscreatetoomuchoverhead,noprogresscanbemade

–  Possiblesolu;ons•  Disableinterrupts•  Pollingmode

Excep;ons

•  Traps–  Systemcallorexecu;onofaprivilegedinstruc;on–  Note:textbookcallsthisa“sozwareinterrupt”

•  Faults–  e.g.,Pagefaults,segmenta;onfault,dividebyzero

–  SimilartoJavaExcep;onhandling–  Notneededforcorrectness,butaperformanceop;miza;on

SystemCalls

•  Applica;oninvokesasystemcalltoexecuteaprivilegedopera;on– Raisesanexcep;on,whichinvokeskernelhandler– Passesparameterstohandler

•  PredefinedSystemCallcode,anyotherarguments…

– Kernelhandlerdoestherest•  savescallercontext(state)•  callspropersystemcallrou;ne•  restorescalledstateandreturns

SystemCallexample:read()1.Userapp:read(file_reference,buffer_addr,n_bytes)

Userspace

Kernelspace

n_bytes

buffer_addr

file_reference

Userstack 2.Pushargumentsontostack

3.CallLibraryprocedureforread()readsyscallcode

inregister

4.Traptokernel

5.KernelHandler 6.readsyscallhandler

7.returntocaller

8.Returnfromread()call

SystemCalls(2)

•  Howdoesthekernelreturnparameterstousermode?– Whatisfile_referenceinread()syscall?

•  Ifit’sthefilename,thenkernelhastoresolvefilenameandlocatefileeach;me

– Whatifkerneljustpasses“address”or“pointer”tothefile?•  Userwouldbereferencingakernelobject(bad)

–  Unixsolu;on:filedescriptors•  Anobjecthandleuniquetoaprocess(literallyaninteger)•  Essen;allyacapabilitytousearesource

Excep;ons

•  Traps–  Systemcallorexecu;onofaprivilegedinstruc;on–  Note:textbookcallsthisa“sozwareinterrupt”

•  Faults–  e.g.,Pagefaults,segmenta;onfault,dividebyzero

–  SimilartoJavaExcep;onhandling–  Notneededforcorrectness,butaperformanceop;miza;on

Faults

•  SomefaultsarefixedsilentlybytheOS– Processresumeswithoutknowledgeoffault– Faulthandlerhandlesinstruc;onresump;on

•  Otherfaultsneedtobehandledbyapplica;on–  Insteadofreturningcontrolfromthefaul;nginstruc;on,OSfaulthandlerreturnscontroltoauser‐levelhandler

– Applica;onsregisteruser‐levelhandlerswithOS•  Unixsignals• WindowsNTAsynchronousProcedureCalls

Faults(2)

•  Fatalfaults–  FaultsthatarenothandledbyOSoruserapplica;on

•  corefilescontainprocessstateforcrashedcprograms

–  ThistypeoffaultwithinthekernelresultsinanOScrash(WindowsBSOD,Unixkernelpanic)

NextTime

•  ReadChapters1and2(thislecture),3,13.1‐13.5(next)

•  Startthinkingaboutprojectgroups.– UseWebCTdiscussionboardtofindpartners.

•  HomeworkandProjectwillbepostedtomorrow.•  FirstPeerWiseques;on&reviewsdueonThursday.

•  CheckWebsiteforcourseannouncements–  hkp://www.cs.ucsd.edu/classes/su09/cse120


Lecture 1: Course Overviewcseweb.ucsd.edu/classes/su09/cse120/lectures/Lecture1.pdf · Recap: Role...

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