11/21/17

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CS61C:GreatIdeasinComputerArchitecture(MachineStructures)

Lecture24:MoreI/O:DMA,Disks,Networking

Instructors:Krste Asanović &RandyH.Katzhttp://inst.eecs.berkeley.edu/~cs61c/fa17

11/21/17 Fall2017 -- Lecture#24 1

Review:AddressTranslationandProtection

• Every instruction and data access needs address translation and protection checks

Good VM design should be fast (~one cycle) and space efficient

Physical Address

Virtual Address

AddressTranslation

Virtual Page No. (VPN) offset

Physical Page No. (PPN) offset

ProtectionCheck

Exception?

Kernel/User Mode

Read/WriteMiss

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Review:HierarchicalPageTables

Level 1 Page TablePage size 10b à1024 x 4096B Level 2

Page Tables12b à 4096B

Data Pages

page in primary memory page in secondary memory

Root of the CurrentPage Table

p1

p2

Virtual Address

(ProcessorRegister)

PTE of a nonexistent page

p1 p2 offset01112212231

10-bitL1 index

10-bit L2 index

Phys

ical

Mem

ory

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Review:TranslationLookasideBuffers(TLB)Address translation is very expensive!

In a two-level page table, each reference becomes three memory accesses

Solution: Cache some translations in TLBTLB hit Þ Single-Cycle TranslationTLB miss Þ Page-Table Walk to refill

VPN offset

V D tag PPN

physical address PPN offset

virtual address

hit?

(VPN = virtual page number)

(PPN = physical page number)

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VM-relatedEventsinPipeline

• HandlingaTLBmissneedsahw orsw mechanismtorefillTLB– Usuallydoneinhardware

• Handlingapagefault(e.g.,pageisondisk)needsprecise trapsosoftwarehandlercaneasilyresumeafterretrievingpage

• Protectionviolationmayabortprocess

PCInst TLB

Inst. Cache D Decode E M

Data TLB

Data Cache W+

TLB miss? Page Fault?Protection violation?

TLB miss? Page Fault?Protection violation?

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AddressTranslation:PuttingitallTogetherVirtual Address

TLBLookup

Page TableWalk

Update TLBPage Fault(OS loads page)

ProtectionCheck

PhysicalAddress(to cache)

miss hit

the page is Ï memory Î memory denied permitted

ProtectionFault

hardwarehardware or softwaresoftware

SEGFAULTWhere?6Fall2017-- Lecture#2411/21/17

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Review:I/O

• “MemorymappedI/O”:Devicecontrol/dataregistersmappedtoCPUaddressspace

• CPUsynchronizeswithI/Odevice:– Polling– Interrupts

• “ProgrammedI/O”:– CPUexecslw/sw instructionsforalldatamovementto/fromdevices– CPUspendstimedoingtwothings:

1. Gettingdatafromdevicetomainmemory2. Usingdatatocompute

11/21/17 Fall2017 -- Lecture#24 7

RealityCheck!

• “MemorymappedI/O”:Devicecontrol/dataregistersmappedtoCPUaddressspace

• CPUsynchronizeswithI/Odevice:– Polling– Interrupts

• “ProgrammedI/O”: DMA– CPUexecslw/sw instructionsforalldatamovementto/fromdevices– CPUspendstimedoing2 things:

1. Gettingdatafromdevicetomainmemory2. Usingdatatocompute

11/21/17 Fall2017 -- Lecture#24 8

Outline

• DirectMemoryAccess• Review:Disks• Networking• StorageAttachmentEvolution• RackScaleMemory• AndinConclusion…

11/21/17 Fall2017 – Lecture#24 9

Outline

• DirectMemoryAccess• Disks• Networking• StorageAttachmentEvolution• RackScaleMemory• AndinConclusion…

11/21/17 Fall2017 – Lecture#24 10

What’sWrongwithProgrammedI/O?

• Notidealbecause…1. CPUhastoexecutealltransfers,couldbedoingotherwork2. Devicespeedsdon’talignwellwithCPUspeeds3. Energycostofusingbeefygeneral-purposeCPUwheresimpler

hardwarewouldsuffice• UntilnowCPUhassolecontrolofmainmemory• 5%ofCPUcyclesonGoogleServersspentinmemcpy()andmemmove()libraryroutines!**Kanev etal.,“Profilingawarehouse-scalecomputer,”ICSA2015,(June2015),Portland,OR.

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PIOvs.DMA

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DirectMemoryAccess(DMA)

• AllowsI/Odevicestodirectlyread/writemainmemory• NewHardware:theDMAEngine• DMAenginecontainsregisterswrittenbyCPU:

– Memoryaddresstoplacedata– #ofbytes– I/Odevice#,directionoftransfer– unitoftransfer,amounttotransferperburst

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OperationofaDMATransfer

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[FromSection5.1.4DirectMemoryAccessinModernOperatingSystemsbyAndrewS.Tanenbaum,HerbertBos,2014]

DMA:IncomingData

1. Receiveinterruptfromdevice2. CPUtakesinterrupt,beginstransfer

– InstructsDMAengine/devicetoplacedata@certainaddress3. Device/DMAenginehandlethetransfer

– CPUisfreetoexecuteotherthings

4. Uponcompletion,Device/DMAengineinterrupttheCPUagain

11/21/17 Fall2017 -- Lecture#24 15

DMA:OutgoingData

1. CPUdecidestoinitiatetransfer,confirmsthatexternaldeviceisready

2. CPUbeginstransfer– InstructsDMAengine/devicethatdataisavailable@certainaddress

3. Device/DMAenginehandlethetransfer– CPUisfreetoexecuteotherthings

4. Device/DMAengineinterrupttheCPUagaintosignalcompletion

11/21/17 Fall2017 -- Lecture#24 16

DMA:SomeNewProblems

• WhereinthememoryhierarchydoweplugintheDMAengine?Twoextremes:– BetweenL1$andCPU:

• Pro:Freecoherency• Con:TrashtheCPU’sworkingsetwithtransferreddata

– BetweenLast-levelcacheandmainmemory:• Pro:Don’tmesswithcaches• Con:Needtoexplicitlymanagecoherency

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Outline

• DirectMemoryAccess• Disks• Networking• AndinConclusion…

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ComputerMemoryHierarchyOneofour“GreatIdeas”

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RackScaleMemory/Storage

Storage-CentricViewoftheMemoryHierarchy

FileSystemCache

StorageController

CacheEmbedded DiskController Cache

Magnetic Disk StorageDisk Array

Optical Disk Jukebox

Magnetic or Optical Tape Library

Shelved Magnetic or Optical Tape

Solid State Disk

RAM

On-Line

Near-Line

Off-Line

FileSystemCache

StorageController

CacheEmbedded DiskController Cache

Magnetic Disk StorageDisk Array

Optical Disk Jukebox

Magnetic or Optical Tape Library

Shelved Magnetic or Optical Tape

Solid State Disk

RAM

On-Line

Near-Line

Off-Line

11/21/17 Fall2017 -- Lecture#24 20

PreviousSlide!

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DRAM

FlashDisk

DiskDevicePerformance(1/2)

• DiskAccessTime=SeekTime+RotationTime+TransferTime+ControllerOverhead– SeekTime=timetopositiontheheadassemblyatthepropercylinder– RotationTime=timeforthedisktorotatetothepointwherethefirstsectorsoftheblockto

accessreachthehead– TransferTime=timetakenbythesectorsoftheblockandanygapsbetweenthemtorotatepast

thehead

Platter

Arm

Actuator

HeadSectorInnerTrack

OuterTrack

ControllerSpindle

11/21/17 Fall2017 -- Lecture#24 22

DiskDevicePerformance(2/2)

• Averagevaluestoplugintotheformula:• RotationTime:Averagedistanceofsectorfromhead?

– 1/2timeofarotation• 7200RevolutionsPerMinuteÞ 120Rev/sec• 1revolution=1/120secÞ 8.33milliseconds• 1/2rotation(revolution)Þ 4.17ms

• Seektime:Averageno.trackstomovearm?– Numberoftracks/3(seeCS186forthemath)– Then,seektime=numberoftracksmoved× timetomoveacrossonetrack

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Butwait!

• Performanceestimatesaredifferentinpractice• Moderndiskshaveon-diskcaches,whicharehiddenfromtheoutsideworld– Generally,whatlimitsrealperformanceistheon-diskcacheaccesstime

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FlashMemory/SSDTechnology

• NMOStransistorwithanadditionalconductorbetweengateandsource/drainwhich“traps”electrons.Thepresence/absenceisa1or0

• Memorycellscanwithstandalimitednumberofprogram-erasecycles.ControllersuseatechniquecalledwearlevelingtodistributewritesasevenlyaspossibleacrossalltheflashblocksintheSSD.

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Administrivia (1/2)• Project3.2(PerformanceContest)hasbeenreleased

– Upto5extracreditpointsforthehighestspeedups• Finalexam:

– 14December,7-10PM@TBA– ContactheadTA(StevenHo)aboutconflictsifyouhaven’tbeencontactedyet

– ReviewLecturesandBookwitheyeontheimportantconceptsofthecourse

• ReviewSessionFriDec8,5-8PM@TBA• ElectronicCourseEvaluationsstartingthisweek!Seehttps://course-evaluations.berkeley.edu

11/21/17 Fall2017 -- Lecture#24 26

Administrivia (2/2)• HW6party tonightnight (Nov21)inthe Woz from 5-8PM

• Nodiscussionsorlabsthisweek!– LabsresumeMondayafterThanksgiving

• Lab11dueinanylabbeforeDecember1• Lab13dueinanyOHbeforeDecember8

• Homework6duetomorrownight• Project4tobereleasedFridaylatest• Homework7tobereleasedMondayafterbreak11/21/17 Fall2017 -- Lecture#24 27

WinnersoftheProject3PerformanceCompetition!

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HappyBirthdayRAID:11/20/87

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RAID(RedundantArraysofInexpensiveDisks)coveredinnextTuesday’slecture!

HappyBirthdayInternet!11/21/69

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CS61cintheNews:Supercomputerina

FileDrawer“TheRaspberryPimodulesletdevelopersfigureouthowtowritethissoftwareandgetittoworkreliablywithouthavingadedicatedtestbedofthesamesize,whichwouldcostaquarterbilliondollarsanduse25megawattsofelectricity.”

GaryGrider,leaderoftheHighPerformanceComputingDivision

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PeerInstructionQuestion• Wehavethefollowingdisk:

– 15000Cylinders,1ms tocross1000Cylinders– 15000RPM=4ms perrotation– Wanttocopy1MB,transferrateof1000MB/s– 1ms controllerprocessingtime

• Whatistheaccesstimeusingourmodel?

DiskAccessTime=SeekTime+RotationTime+TransferTime+ControllerProcessingTime

A B C D

10.5 ms 9 ms 8.5ms 11.5ms

11/21/17 Fall2017 -- Lecture#24 33

Outline

• DirectMemoryAccess• Disks• Networking• StorageAttachmentEvolution• RackScaleMemory• AndinConclusion…

11/21/17 Fall2017 – Lecture#24 34

Networks:TalkingtotheOutsideWorld

• OriginallysharingI/Odevicesbetweencomputers– E.g.,printers

• Thencommunicatingbetweencomputers– E.g.,filetransferprotocol

• Thencommunicatingbetweenpeople– E.g.,e-mail

• Thencommunicatingbetweennetworksofcomputers– E.g.,filesharing,www,…

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• History– 1963:JCRLicklider,whileatDoD’s ARPA,writesamemodescribingdesiretoconnectthecomputersatvariousresearchuniversities:Stanford,Berkeley,UCLA,...

– 1969:ARPAdeploys4“nodes”@UCLA,SRI,Utah,&UCSB

– 1973RobertKahn&Vint CerfinventTCP,nowpartoftheInternetProtocolSuite

• Internetgrowthrates– Exponentialsincestart!

TheInternet(1962)www.computerhistory.org/internet_history

www.greatachievements.org/?id=3736en.wikipedia.org/wiki/Internet_Protocol_Suite

“Lick”

Vint Cerf“Revolutions like this don't

come along very often”

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• “SystemofinterlinkedhypertextdocumentsontheInternet”

• History– 1945:Vannevar Bushdescribeshypertextsystemcalled“memex”inarticle

– 1989:SirTimBerners-LeeproposedandimplementedthefirstsuccessfulcommunicationbetweenaHypertextTransferProtocol(HTTP)clientandserverusingtheinternet.

– ~2000Dot-comentrepreneursrushedin,2001bubbleburst

• Today:Accessanywhere!

TheWorldWideWeb(1989)en.wikipedia.org/wiki/History_of_the_World_Wide_Web

Tim Berners-LeeWorld’s First web

server in 1990

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Sharedvs.Switch-BasedNetworks

• Sharedvs.Switched:• Shared:1atatime(CSMA/CD)• Switched: pairs(“point-to-point”connections)communicateatsametime

• Aggregatebandwidth(BW)inswitchednetworkismanytimesthatofshared:• Point-to-pointfastersincenoarbitration,simplerinterface

Node Node Node

Shared

CrossbarSwitch

Node

Node

Node

Node

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WhatMakesNetworksWork?• Links connectingswitchesand/orrouters toeachotherandtocomputersordevices

Computer

networkinterface

switch

switch

switch

• Abilitytonamethecomponentsandtoroutepacketsofinformation-messages- fromasourcetoadestination

• Layering,redundancy,protocols,andencapsulationasmeansofabstraction(61Cbigidea)

11/21/17 Fall2017 -- Lecture#24 39

SoftwareProtocoltoSendandReceive• SWSendsteps

1:ApplicationcopiesdatatoOSbuffer2:OScalculateschecksum,startstimer3:OSsendsdatatonetworkinterfaceHWandsaysstart

• SWReceivesteps3:OScopiesdatafromnetworkinterfaceHWtoOSbuffer2:OScalculateschecksum,ifOK,sendACK;ifnot,deletemessage (senderresendswhentimerexpires)

1:IfOK,OScopiesdatatouseraddressspace,&signalsapplicationtocontinue

11/21/17 Fall2017 -- Lecture#24 40

Header Payload

Checksum

TrailerCMD/Address/DataNetID NetID Len ACK

INFO

Dest Src

NetworksarelikeOgres

https://www.youtube.com/watch?v=_bMcXVe8zIs

11/21/17 Fall2017 -- Lecture#24 41

Protocols for Networks of Networks?Whatdoesittaketosendpacketsacrosstheglobe?• Bitsonwireorair• Packetsonwireorair• Deliverypacketswithinasinglephysicalnetwork• Deliverpacketsacrossmultiplenetworks• Ensurethedestinationreceivedthedata• Createdataatthesenderandmakeuseofthedataatthereceiver

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Lotstodoandatmultiplelevels!

Useabstraction tocopewithcomplexityofcommunication

•Networksarelikeogres onions•Hierarchyoflayers:

- Application(chatclient,game,etc.)- Transport(TCP,UDP)- Network(IP)- DataLinkLayer(ethernet)- PhysicalLink(copper,wireless,etc.)

ProtocolforNetworksofNetworks?

11/21/17 Fall2017 -- Lecture#24 43

ProtocolFamilyConcept• Protocol:packetstructureandcontrolcommandstomanagecommunication

• Protocolfamilies(suites):asetofcooperatingprotocolsthatimplementthenetworkstack

• Keytoprotocolfamilies isthatcommunicationoccurslogically atthesameleveloftheprotocol,calledpeer-to-peer…

…butisimplementedviaservicesatthenextlowerlevel• Encapsulation:carryhigherlevelinformationwithinlowerlevel“envelope”

11/21/17 Fall2017 -- Lecture#24 44

Dear Bill,

Your days are numbered.

--Steve

• CEO A writes letter to CEO B– Folds letter and hands it to assistant

• Assistant:– Puts letter in envelope with CEO B’s full name– Takes to FedEx

• FedEx Office– Puts letter in larger envelope– Puts name and street address on FedEx envelope– Puts package on FedEx delivery truck

• FedEx delivers to other company

Inspiration …

11/21/17 Fall2017 -- Lecture#24 45

CEO

Aide

FedEx

CEO

Aide

FedExLocationFedex Envelope(FE)

The Path of the Letter

Letter

Envelope

SemanticContent

Identity

“Peers”oneachsideunderstandthesamethingsNooneelseneedsto

Lowestlevelhasmostpackaging

11/21/17 Fall2017 -- Lecture#24 46

ProtocolFamilyConcept

Message Message

TH Message TH Message TH TH

Actual Actual

Physical

Message TH Message THActual ActualLogical

Logical

Eachlowerlevelofstack“encapsulates”informationfromlayerabovebyaddingheaderandtrailer

11/21/17 Fall2017 -- Lecture#24 47

MostPopularProtocolforNetworkofNetworks

• TransmissionControlProtocol/InternetProtocol(TCP/IP)• ThisprotocolfamilyisthebasisoftheInternet,aWAN(wideareanetwork)protocol– IPmakesbestefforttodeliver– Packetscanbelost,corrupted– TCPguaranteesdelivery– TCP/IPsopopularitisusedevenwhencommunicatinglocally:evenacrosshomogeneousLAN(localareanetwork)

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Message

TCP/IPPacket,EthernetPacket,Protocols

• Applicationsendsmessage

TCP data

TCP HeaderIP Header

IP DataEH

Ethernet Hdr

Ethernet Hdr• TCPbreaksinto64KiBsegments,adds20Bheader

• IPadds20Bheader,sendstonetwork

• IfEthernet,brokeninto1500Bpacketswithheaders,trailers

11/21/17 Fall2017 -- Lecture#24 49 5011/21/17 Fall2017 - Lecture#20

Outline

• DirectMemoryAccess• Disks• Networking• StorageAttachmentEvolution• RackScaleMemory• AndinConclusion…

11/21/17 Fall2017 – Lecture#24 51

StorageAttachmentEvolution

Host

OS

Disk Interface (DI)

AllocationTable

Disk, Cylinder,Track,

Sector

LAN

Host

Host

HostNetwork

FileServer

OS

NetworkInterface

(NI)

NetworkInterface

(NI)

NetworkInterface

(NI)

File Name, Offset, LengthDirectAttachment

NetworkServerAttachment

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StorageAttachmentEvolution

DiskStorage

Subsystem

WorkStation

MainFrame

MainFrame

ChannelInterface

OSOSLUN,

Offset,Length

LUNToPHY

LAN

Host

Host

Host

NetworkFile

Server

OS

NetworkInterface

(NI)

NetworkInterface

(NI)

NetworkInterface (NI)

Network-attachedStorage (NAS)

OSOS

File Name, Offset, Length

Disk, Cylinder,Track, Sector

11/21/17 Fall2017 -- Lecture#24 53

NetworkAttached

ChannelAttached

OpticalDisk

StorageSubsystem

SAN

MainFrame

DiskStorage

Subsystem

TapeStorage

Subsystem

ChannelInterface

LAN

Host

Host

Host

NetworkInterface

(NI)

NetworkInterface

(NI)

NetworkInterface

(NI)

File Name, Offset, Length

FileServer

FileServer

FileServer

CI

LUN,Offset,Length

Gateway

WAN

Gateway

LAN SAN

MainFrame

FS DSS

Remote SAN

CI

CI

CI

LUN,Offset, Length

PHY Device,Cyl, Trk, Sector

StorageAttachmentEvolution

11/21/17 Fall2017 -- Lecture#24 54

StorageAreaNetworks(SAN)

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Outline

• DirectMemoryAccess• Disks• Networking• StorageAttachmentEvolution• RackScaleMemory• AndinConclusion…

11/21/17 Fall2017 – Lecture#24 55

StorageClassMemoryakaRack-ScaleMemory

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StorageClassMemoryakaRack-ScaleMemory

• Highbandwidthandlowlatencythroughasimplifiedinterfacebasedonmemorysemantics(i.e.,ld/st),scalablefromtenstoseveralhundredGB/secofbandwidth,withsub-100nanosecs load-to-usememorylatency

• Supportsscalablememorypoolsandresourcesforreal-timeanalyticsandin-memoryapplications(i.e.,map-reduce)

• Highlysoftwarecompatiblewithnorequiredchangestotheoperatingsystem

• Scalesfromsimple,lowcostconnectivitytohighlycapable,rackscaleinterconnect

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StorageClassMemoryakaRack-ScaleMemory

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CheaperthanDRAMMoreexpensivethandiskNon-Volatileandfasterthandisk

StorageClassMemoryakaRackScaleMemory

• Systemmemoryisflatorshrinking– Memorybandwidthpercorecontinuestodecrease– Memorycapacitypercoreisgenerallyflat– MemoryischangingonadifferentcadencecomparedtotheCPU

• Dataisgrowing– Datathatrequiresreal-timeanalysisisgrowingexponentially– Thevalueoftheanalysisdecreasesifittakestoolongtoprovideinsights

• Industryneedsanopenarchitecturetosolvetheproblems– Memorytierswillbecomeincreasinglyimportant– Rack-scalecomposability requiresahighbandwidth,lowlatencyfabric– MustseamlesslyplugintoexistingecosystemswithoutrequiringOSchanges

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RemoteDirectMemoryAccess

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RemoteDirectMemoryAccess

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ConventionalNetworking

Cut-throughMemoryaccessOvernetwork

Outline

• DirectMemoryAccess• Disks• Networking• RackScaleMemory• And,inConclusion…

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“And,inConclusion…”

• I/Ogivescomputerstheir5senses• I/Ospeedrangeis100-milliontoone• DMAtoavoidwastingCPUtimeondatatransfers• Disksforpersistentstorage,beingreplacedbyflashandemerging“storageclassmemory”

• Networks:computer-to-computerI/O– Protocolsuitesallownetworkingofheterogeneouscomponents.GreatIdea:LayersandAbstraction

– Emergingclass:Rack-scale/Storage-classMemoryaccessibleoverRDMAorothernetworkinterconnect

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