Red Hat LINUX VIRTUAL SERVER 4.7 - ADMINISTRATION Dokumentacja Pobierz pdf (Strona 18)

Installing and Configuring Linux Guest Operating Systems

Theideaofguest‐hostinteractionisnotanewconcept.IthaslongbeenapartofVMwareproductsintheform

ofVMwareTools.Forexample:

 TheVMwareSVGAdriversharesdatastructureswiththehypervisortoallowfasterscreenupdates.

 TheVMwarehigh‐performancevirtualEthernetdriver,vmxnet,sharesdatastructureswiththe

hypervisortoreduceCPUoverhead.

 TheVMware“balloondriver”isusedbythehypervisortocontroltheguestoperatingsystem’smemory

usage.

 TheVMwareToolsserviceenablestimesynchronizationbetweenhostandguest.

Whilesuchguest‐hostcommunicationprovidesimprovedperformanceandcanbeclassifiedas

paravirtualization,noneoftheseexamplesinvolvechangestotheunderlyingguestoperatingsystemkernel.

However,inordertoparavirtualizetheCPUandthememorymanagementunit,changes

totheguest

operatingsystemkernelarerequired.Open‐sourceoperatingsystems,suchasLinux,allowustomakesuch

changes.

Virtual Machine Interface

Earlyparavirtualizationrequiredoperatingsystemsandapplicationstobecertifiedonmanydifferent

kernels—somefornativehardwareandotherstorunonahypervisor.Also,thelackofastandardguest‐host

interfaceledtofrequentinterfacechanges,whichinturncausedversiondependenciesbetweentheguest

operatingsystemkerneland

thehypervisor.Inordertoaddresstheseissues,VMwareproposedanew

guest‐hostinterface,calledVirtualMachineInterface,whichdefinesasetofhypercallsanoperatingsystem

canusetocommunicatewiththehypervisor.Fordetails,seetheParavirtualizationAPIVersion2.5

specification.Foralink,see“Resources”on

page 19.

ThestandardizedinterfaceprovidedbyVMIallowstheguestoperatingsystemkernelandthehypervisorto

evolveindependently.TheVMIspecificationalsomakesitpossibleforothervendorstoenabletheir

hypervisorstosupportguestoperatingsystemsthatuseVMI.

VMIwasdesignedtoabstractnativehardware.Thisfeature,called

transparentparavirtualization,allowsa

VMI‐enabledkerneltorunbothonnativehardwareandonhypervisorsthatsupporttheinterfacewithno

additionalmodificationtotheoperatingsystemkernel.

VMIcodeisincludedin32‐bitLinuxmainlinekernels2.6.22andabove.TheUbuntuLinuxdistribution

includesVMIsupportinversion

7.04(FeistyFawn)andlater.NovellincludesVMIsupportinSUSELinux

EnterpriseServer10SP2.ToenableVMI,see“AppendixC:EnablingVMIinaLinuxKernelandinESX3.5”

onpage 22.

VMI Performance Benefits

TheVMwareimplementationofVMIoffersanumberofperformanceandresource‐utilizationbenefits:

 Thesyscallentryandexitpathisfaster.Thisspeedsupsyscall‐dominatedworkloads.

 VMI‐enabledLinuxkernelsbydefaultuseanalternatetimerinterruptmechanismthatresultsinreduced

physicalCPUconsumption,especiallywhenthevirtualmachineisidle,andinmoreaccurate

timekeeping,evenwhenrunningmanyvirtualmachines.

 Becausetheguestkernelcommunicatestothehypervisoritsintenttoperformmemorymanagementunit

(MMU)‐relatedoperations,MMUvirtualizationoverheadisreduced.Dependingontheworkload,this

canhavevaryingperformancebenefits.

 SMPvirtualmachinesrunningVMI‐enabledoperatingsystemsusesharedshadowpagetables.Asa

resulttheyhavelessmemoryspaceoverheadthanthoserunningnon‐VMI‐enabledoperatingsystems.

Formoreinformationonshadowpagetables,seethepaper“ESXServerArchitectureandPerformance

Implications.”Foralink,see“Resources”

onpage 19.

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