Linux 系统流程和性能管理 2.docx
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Linux 系统流程和性能管理 2.docx
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Linux系统流程和性能管理2
Systemperformance
Foranysystem,continuedcustomersatisfactionandpurchasingdecisions
dependstronglyonperformance.Partofthejobofthesystemadministratoris
performanceanalysis:
Tounderstandthesystembehaviorandidentifytheusage
ofresources.
Thissectionprovidesinformationonconcepts,tools,andtechniquesfor
assessingandtuningtheperformanceofAIXonRS/6000systems.Topics
coveredincludeassessmentofCPUuse,memoryuse,diskI/O,and
communicationsI/O.Theconcepts,tools,andtechniquesdiscussedinthis
sectionarenotintendedtobeatotallist,and,assuch,youareencouragedto
seekadditionalinformationfromtheappropriateAIXproductdocumentation.
Systemdynamicsandworkload
Anaccurateandcompletedefinitionofthesystem'sworkloadiscriticalto
predictingorunderstandingitsperformance.Adifferenceinworkloadcancause
farmorevariationinthemeasuredperformanceofasystemthandifferencesin
CPUclockspeedorRAMsize.Theworkloaddefinitionmustincludenotonlythe
typeandrateofrequeststothesystembutalsotheexactsoftwarepackagesand
in-houseapplicationprogramstobeexecuted.
Wheneverpossible,normalusageofexistingapplicationsshouldbeobservedto
getauthentic,real-worldmeasurementsoftheratesatwhichusersinteractwith
theirworkstationsorterminals.
Makesurethatyouincludetheworkloadthatyoursystemisdoingbehindthe
scenes.Forexample,ifyoursystemcontainsfilesystemsthatareNFS-mounted
andfrequentlyaccessedbyothersystems,handlingthoseaccessesisprobably
asignificantfractionoftheoverallworkloadeventhoughyoursystemisnot
officiallyaserver.
Systemdynamics
Itisnotenoughtohavethemostefficientprograms.Inmanycases,theactual
programsbeingrunareoutsideofthecontrolofthepersonwhoisresponsibleformeetingtheorganization'sperformanceobjectives.Oncetheapplication
programshavebeenacquiredorimplementedasefficientlyaspossible,further
improvementintheoverallperformanceofthesystembecomesamatterof
systemtuning.Themaincomponentsthataresubjecttosystem-leveltuningare:
FixeddiskTheLogicalVolumeManager(LVM)controlsthe
placementoffilesystemsandpagingspacesonthedisk,
whichcansignificantlyaffecttheamountofseeklatency
thesystemexperiences.ThediskdevicedriverscontroltheorderinwhichI/Orequestsareactedon.
RealmemoryTheVirtualMemoryManager(VMM)controlsthepoolof
freereal-memoryframesanddetermineswhenandfrom
whomtostealframestoreplenishthepool.
RunningthreadTheschedulerdetermineswhichdispatchableentity
shouldreceivecontrolnext.InAIXthedispatchableentitychangesfromaprocesstoathread.
CommunicationsI/ODependingonthetypeofworkloadandthetypeof
communicationslink,itmaybenecessarytotuneoneor
moreofthecommunicationsdevicedrivers,TCP/IP,or
NFS.
Classesofworkloads
Workloadstendtofallnaturallyintoasmallnumberofclasses.Thetypesthat
followaresometimesusedtocategorizesystems.However,sinceasingle
systemisoftencalledupontoprocessmultipleclasses,workloadseemsmore
aptinthecontextofperformance.
WorkstationAworkloadthatconsistsofasingleusersubmittingworkthrough
thenativekeyboardandreceivingresultsonthenativedisplayof
thesystem.Typically,thehighest-priorityperformanceobjective
ofsuchaworkloadisminimumresponsetimetotheuser'srequests.
MultiuserAworkloadthatconsistsofanumberofuserssubmittingwork
throughindividualterminals.Typically,theperformance
objectivesofsuchaworkloadareeithertomaximizesystem
throughputwhilepreservingaspecifiedworst-caseresponse
timeortoobtainthebestpossibleresponsetimeforafairly
constantworkload.
ServerAworkloadthatconsistsofrequestsfromothersystems.For
example,afile-serverworkloadismostlydiskread/write
requests.Inessence,itisthedisk-I/Ocomponentofamultiuser
workload(plusNFSorDFSactivity);so,thesameobjectiveof
maximumthroughputwithinagivenresponse-timelimitapplies.
Otherserverworkloadsconsistofcompute-intensiveprograms,
databasetransactions,printjobs,andsoon.
Whenasinglesystemisprocessingworkloadsofmorethanonetype,theremust
beaclearunderstandingbetweentheusersandtheperformanceanalystasto
therelativeprioritiesofthepossiblyconflictingperformanceobjectivesofthe
differentworkloads.
Generalperformanceandavailabilityguidelines
Therearesomebasicguidelinesthatcanhelpwiththeconfigurationofsystems,
dependingontheirintendeduse.Theseareoutlinedbrieflyasfollows:
∙Multi-threadedapplicationsbenefitthemostfrommultipleCPUs.
∙I/OintensiveapplicationsbenefitthemostfrommultipleI/Oadaptersand
manydiskdrives.
∙Additionalmemoryisneverdisadvantageous.
∙Dataavailabilitycanbeincreasedbyusinghardwareorsoftwaremirroring.
∙Whenintendingtohaveabackupserverforuseincaseofafailureinthe
primaryserver,itshouldbeasidenticaltotheprimaryserveraspossible,
preferablyanexactduplicate.
Overviewofsystemperformance
TheAIXBaseOperatingSystemcontainsanumberofmonitoringandtuning
toolsthathavehistoricallybeenpartofUNIXsystemsorarerequiredtomanage
theimplementation-specificfeaturesofAIX.TheBOSfunctionsandcommands
thataremostimportanttoperformanceanalystsare:
iostatReportsCPUandI/Ostatistics.
vmstatReportsvirtual-memoryactivityandothersystemstatistics.
netstatDisplaysthecontentsofnetwork-relateddatastructures.
psDisplaysthestatusofprocesses.
lsattrDisplaystheattributesofdevices.
lslvDisplaysinformationaboutalogicalvolumeorthelogicalvolume
allocationsofaphysicalvolume.
nfsstatDisplaysstatisticsaboutNetworkFileSystem(NFS)andRemote
ProcedureCall(RPC)activity.
niceRunsacommandathigher-orlower-than-normalpriority.
noDisplaysorsetsnetworkoptions.
reniceChangesthepriorityofoneormoreprocesses.
reorgvgReorganizesthephysical-partitionallocationwithinavolumegroup.
sarCollectsandreportsorrecordssystem-activityinformation.
schedtuneSetsparametersforCPUschedulerandVirtualMemoryManager
processing.
svmonCapturesandanalyzesasnapshotofvirtualmemory.
timePrintstheelapsedexecutiontimeandtheuserandsystem
processingtimeattributedtoacommand.
tprofReportsCPUusageforindividualprogramsandthewholesystem.
traceRecordsandreportsselectedsystemevents.
Inthefollowingsection,asubsetofthesefunctionsandcommandsisdiscussed.
BaseOperatingSystemtools
Thefollowingcommandsarethefocusthroughoutthissection.
_vmstat
_iostat
_netstat
_sar
Usingthevmstatcommand
Thevmstatcommandsyntaxisasfollows:
vmstat[-f][-i][-s][PhysicalVolume...][Interval[Count]]
Thevmstatcommandreportsstatisticsaboutkernelthreads,virtualmemory,
disks,traps,andCPUactivity.Reportsgeneratedbythevmstatcommandcan
beusedtobalancesystemloadactivity.Thesesystem-widestatistics(amongall
processors)arecalculatedeitherasaveragesforvaluesexpressedas
percentages,orassums.ThePhysicalVolumeparametercanbeusedtospecifyonetofournames.
Transferstatisticsaregivenforeachspecifieddriveintheorderspecified.This
countrepresentslogicalandphysicalrequeststothephysicaldevice.Itdoesnot
implyanamountofdatathatwasreadorwritten.Severallogicalrequestscanbe
combinedintoonephysicalrequest.
Ifthevmstatcommandisinvokedwithoutflags,thereportcontainsasummaryofthevirtualmemoryactivitysincesystemstartup.Ifthe-fflagisspecified,the
vmstatcommandreportsthenumberofforkssincesystemstartup.The
PhysicalVolumeparameterspecifiesthenameofthephysicalvolume.
TheIntervalparameterspecifiestheamountoftimeinsecondsbetweeneach
report.Thefirstreportcontainsstatisticsforthetimesincesystemstartup.
Subsequentreportscontainstatisticscollectedduringtheintervalsincethe
previousreport.IftheIntervalparameterisnotspecified,thevmstatcommand
generatesasinglereportandthenexits.
TheCountparametercanonlybespecifiedwiththeIntervalparameter.Ifthe
Countparameterisspecified,itsvaluedeterminesthenumberofreports
generatedandthenumberofsecondsapart.IftheIntervalparameterisspecified
withouttheCountparameter,reportsarecontinuouslygenerated.ACount
parameterofzero(0)isnotallowed.
Thekernelmaintainsstatisticsforkernelthreads,paging,andinterruptactivity,
whichthevmstatcommandaccesses.Thediskinput/outputstatisticsare
maintainedbydevicedrivers.Fordisks,theaveragetransferrateisdetermined
byusingtheactivetimeandnumberoftransfersinformation.Thepercentactive
timeiscomputedfromtheamountoftimethedriveisbusyduringthereport.
Keyflagsforthevmstatcommand
Examples
Thefollowingaresomeexamplesusingthevmstatcommand.
1.Todisplayasummaryofthestatisticssinceboot,entervmstat.Asample
outputfollows:
2.Todisplayfivesummariesat2-secondintervals,entervmstat25.Asample
outputfollows:
Thefirstsummary(lineoneofthereport)containsstatisticsforthetimesince
boot.
Note:
Boththe-fand-sflagscanbeenteredonthecommandline,butthe
systemwillonlyacceptthefirstflagspecifiedandwilloverridethesecond
flag.
FlagDescription
-fReportsthenumberofforkssincesystemstartup.
-iDisplaysthenumberofinterruptstakenbyeachdevicesincesystem
startup.
-sWritestostandardoutpu
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