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COMP9242

2010/S2 Week 7

Device Drivers

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Lecture outline

Part 1: Introduction to device drivers

Part 2: Overview of research on device driver reliability

Part 3: Device drivers research at ERO!

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User app

OS

driver driver driver driver

User app User app

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!o"e statistics

#$% of O! code is in device drivers

& 3'(()'$$$ out of ('**#'$$$ loc in Linu+ 2,-,2#

. ty/ical Linu+ la/to/ runs 02($'$$$ lines of ernel code'

includin 0#2'$$$ loc in 3- different device drivers

Drivers contain 3# ti"es "ore bus /er loc than the rest ofthe ernel

#$% of O! failures are caused by driver bus

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Part 1: Introduction to device drivers

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O! archeoloy

he first 456 device drivers: I7O libraries for the I89#$* batch /rocessin syste" 1*;)level view

#us inter"ace

interna$ $oic

reister "i$e

8/O #us

e'terna$ !ediu!

8/O

dev

ice

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I7O devices in a ty/ical desto/ syste"

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P?I bus overview

P?I bus& ?onventional P?I

Develo/ed and standardised in early *$Cs

32 or -( bit shared /arallel bus

@/ to --9B 4;33987s6

& P?I> @/ to 1339B 41$--987s6

& P?I E+/ress

?onsists of serial /2/ lins

!oftware>co"/atible with conventional P?I

@/ to 1-=87s /er device

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P?I bus overview: "e"ory s/ace

CPU

MPC8

contro$$er

Dev1 Dev

Dev1 Dev2 Dev

Dev2

P%+sica$ address space S3

PC8 !e!or+ space

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P?I bus overview: D9.

CPU

MPC8

contro$$er

Dev1 Dev

Dev1 Dev2 Dev

Dev2


PC8 !e!or+ space

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P?I bus overview: D9.

CPU

MPC8

contro$$er

Dev1 Dev

Dev1 Dev2 Dev

Dev2


PC8 !e!or+ space

8OMMU

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D9. descri/tors

M

Device

Driver

Per!anent DM !appins

Set up durin driver initia$isationData !ust #e copied to/"ro! DM #u""ers

M

Device

Driver

Strea!in !appins

Created "or eac% trans"erData is accessed inp$ace

DM descriptors

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P?I bus overview: interru/ts

CPU

MPC8

contro$$er

Dev1 Dev

Dev1 Dev2 Dev

8;

contro$$er

Dev2


PC8 !e!or+ space

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P?I bus overview: confi s/ace

P?I confiuration s/ace

& @sed for device enu"eration and confiuration& ?ontains standardised device descri/tors

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P?I bus overview: I7O s/ace

I7O s/ace

& obsolete

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Fritin a driver for a P?I device

Reistration

& ell the O! which P?I device IDCs the driver su//orts

Instantiation

& Done by the O! when it finds a driver with a "atchin ID

Initialisation

& .llocate P?I resources: "e"ory reions' IRGCs

& Enable bus "asterin

Power "anae"ent

& Pre/are the device for a transition into a low>/ower state

& Restore device confiuration durin wae>u/

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Fritin a driver for a P?I device

Interru/t handler

& Return .!.P to re>enable interru/tsH /erfor" heavy>weiht/rocessin in a se/arate thread

D9.

& Per"anent "a//ins: disable cachin

& !trea"in "a//ins: "ay reuire bounce buffers& Returns buffer address in the bus address s/ace

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@!8 bus overview

@!8 bus& Bost>centric

& Distributed>syste">style architecture

& Bot /lu

& Power "anae"ent

8us>/owered and self>/owered devices& @!8 1,+

@/ to 129b7s

& @!8 2,$

@/ to ()$9b7s

& @!8 3,$ @/ to (,)=b7s

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@!8 bus overview

US #us

contro$$er

oot %u#

Device 1 Device 2

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I7O devices in a ty/ical desto/ syste"

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Driver stacin

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Driver stacin

=CP/8P stack

>??772

@t%ernet

driver

%ardAstartA'!itpkt3

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Driver stacin

=CP/8P stack

>??772

@t%ernet

driver

US @

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Driver stacin

=CP/8P stack

>??772

@t%ernet

driver

US @

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Driver stacin

=CP/8P stack

>??772

@t%ernet

driver

US @

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Driver fra"ewor desin /atterns

=%e driver pattern =%e #us pattern

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Driver fra"ewor software architecture

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Guestions5

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Part 2: Overview of research on device driverreliability

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!o"e statistics

#$% of O! code is in device drivers

& 3'(()'$$$ out of ('**#'$$$ loc in Linu+ 2,-,2#

. ty/ical Linu+ la/to/ runs 02($'$$$ lines of ernel code'includin 0#2'$$$ loc in 3- different device drivers

Drivers contain 3# ti"es "ore bus /er loc than the rest ofthe ernel

#$% of O! failures are caused by driver bus

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@nderstandin driver bus

Driver failures

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@nderstandin driver bus

Driver failures

& 9e"ory access violations

& O! /rotocol violations

Orderin violations

Data for"at violations

E+cessive use of resources e"/oral failure

& Device /rotocol violations

Incorrect use of the device state "achine

Runaway D9.

Interru/t stor"s& ?oncurrency bus

Race conditions

Deadlocs

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@ser>level device drivers

@ser>level drivers

& Each driver is enca/sulated inside a se/arate hardware/rotection do"ain

& ?o""unication between the driver and its client is based on IP?

& Device "e"ory is "a//ed into the virtual address s/ace of thedriver

& Interru/ts are delivered to the driver via IP?Cs

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@ser>level drivers in J>ernel O!s

pp$ication=CP/8PDriver

8PC8PC

DM

User $and

Berne$

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pp$ication=CP/8PDriver

8PC8PC

8PC

8;

User $and

Berne$

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pp$ication

=CP/8PDriver

8PC

et "i$ter

User $and

Berne$

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pp$icationDriver

8PC

=CP/8P

User $and

Berne$

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Driver /erfor"ance characteristics

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Driver /erfor"ance characteristics

I7O throuh/ut

& ?an the driver saturate the device5

I7O latency

& Bow does the driver affect the latency of a sinle I7O reuest5

?P@ utilisation

& Bow "uch ?P@ overhead does the driver introduce5

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I"/rovin the /erfor"ance of @LD

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I"/rovin the /erfor"ance of @LD

Fays to i"/rove user>level driver /erfor"ance

& !hared>"e"ory co""unication& Reuest ueuein

& Interru/t coalescin

I"/le"entin efficient shared "e"ory

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I"/le"entin efficient shared>"e"oryco""unication

Issues:

& Resource accountin& !afety

& .synchronous notifications

Consu!erProducer

User $and

Berne$ noti"ications

s%ared !e!or+

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Rbufs

Pro/osed in the Ke"esis "icroernel>based "ulti"edia O!

Consu!erProducer data reion

r(ro

ror(re)uest descriptors

response descriptors

%ead pointer

tai$ pointer

%ead pointer

tai$ pointer

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Early i"/le"entations

9ichian er"inal !yste" 1*#$Cs/ersonality J>ernel>based "ulti>server O!

& Bih IP? overhead

& Eventually' "oved drivers bac into the ernel

L3 1*)#>1**3ernel>based O!

& Bih IP? overhead& I"/roved IP? desin: 2$>fold /erfor"ance i"/rove"ent

& Ko data on driver /erfor"ance available

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9ore recent i"/le"entations

!aw"ill 02$$$ti"e O!

& 01$$% ?P@ overhead due to user>level drivers

Alue 1**-s/ace distributed L(>based O!

& Low>overhead user>level I7O de"onstrated for a dis driver

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?urrently active syste"s

Research

& seL(

& 9IKI3

& Ke+us

?o""ercial

& OL(

& GK

& =reenBills IKE=RIM

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@ser>level drivers in a "onolithic O!

pp$icationDriver

=CP/8P

User $and

inu' Berne$

en es$ie et a$- User$eve$ device drivers: c%ieved per"or!ance* 2006

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pp$icationDriver

=CP/8P

User $and

inu' Berne$


send3

read3

Me!!apped 8/O

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pp$icationDriver

=CP/8P

User $and

inu' Berne$


recv3

8;

read3

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pp$icationDriver

=CP/8P

User $and

inu' Berne$


pciA!apAxxx3 s+sca$$PC8 #us address

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Perfor"ance

& @/ to #% throuh/ut deradation

& @/ to 1#% ?P@ overhead

& .ressive use of interru/t rate li"itin /otentially affects

latency 4not "easured6,

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Koos

. co"/lete device>driver reliability solution for Linu+:

& Aault isolation& Aault detection

& Recovery

inu' kerne$

readon$+ "or t%e driver3

Driver

PCECop+in/rep$ication

EC%eckin

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Koos



& Recovery

inu' kerne$

readon$+ "or t%e driver3

Driver

PCECop+in/rep$ication

EC%eckin

Driver

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K

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Koos



& Recovery

Proble"s

& he driver interface in Linu+ is not well defined, Koos "ustsi"ulate the behaviour of hundreds of ernel and driver entry/oints,

Perfor"ance

& 1$% throuh/ut deradation

& )$% ?P@ overhead

Ni t li ti d l l d i

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Nirtualisation and user>level drivers

Direct I7O

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Nirtualisation and user>level drivers

Paravirtualised I7O

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Paravirtualised I7O in en

>en %+pervisor

Driver do!ain Guest do!ain

net"rontnet#ack

Driver

8/O c%anne$s

=>t' #u"

"ree #u"

> r' #u"r' packet

en I7O channels are si"ilar to rbufs' but use a sinlecircular buffer for both reuests and co"/letions and rely on

"a//in rather than sharin

I7O h l

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en I7O channels

P i t li d I7O i

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Paravirtualised I7O in en

Perfor"ance overhead of the oriinal i"/le"entation: 3$$%

& Lon critical /ath 4increased instructions /er /acet6

& Biher L8 and cache "iss rates 4"ore cycles /er instructions6

& Overhead of "a//in

O/ti"isations

& .void "a//in on the send /ath 4the driver does not need tosee the /acet content6

& Re/lace "a//in with co/yin on the receive /ath

& .void unalined co/ies

& O/ti"ised i"/le"entation of /ae "a//in

& ?P@ overhead down to *#% 4worst>case receive /ath6

Other driver reliability techniues

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I"/le"entin drivers usin safe lanuaes

& Qava O!s: affeO!' Q

Every /rocess runs in a se/arate /rotection do"ain with a/rivate hea/, Process boundaries are enforced by thelanuae runti"e, ?o""unication is based on sharedhea/s,

& Bouse 4Basell O!6 8are>"etal Basell runti"e, he ernel and drivers are in

Basell,

@ser /rora"s can be written in any lanuae,

& !afeDrive

E+tends ? with /ointer ty/e annotations enforced via staticand runti"e checin

unsigned n;

struct e1000 buffer * count(n) bufinfo;


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I"/le"entin drivers usin safe lanuaes

& !inularity O!

he entire O! is i"/le"ented in !in

Every driver is enca/sulated in a se/arate software>isolated/rocess

Processes co""unicated via "essaes sent across channels

!in /rovides "eans to s/ecify and statically enforcechannel /rotocols


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!tatic analysis

& !L.9' 8last' ?overity

& =eneric /rora""in faults

Release acuired locsH do not acuire a loc twice

Do not dereference user /ointers

?hec /otentially K@LL>/ointers returned fro" routine

& Driver>s/ecific /ro/erties

if a driver calls another driver that is lower in the stac'then the dis/atch routine returns the sa"e status that wasreturned by the lower driver

drivers "ar I7O reuest /acets as /endin while ueuin

the"& Li"itations

9any /ro/erties are beyond reach of current tools or aretheoretically undecidable 4e,,' "e"ory safety6

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Guestions5

07 drivers

Documents