Android Performance Case Study, Falcon Pro

2/23/2015 AndroidPerformanceCaseStudy,FalconPro

http://www.curiouscreature.com/docs/androidperformancecasestudy1.html 1/25

AndroidPerformanceCaseStudybyRomainGuywww.curiouscreature.org

FalconProIrecentlyinstalledFalconPro,anewTwitterclient,onmyNexus4.IreallyenjoyusingthisapplicationbutInoticedafewhiccupshereandtherewhileusingitanditseemedthatscrollingthemaintimelinedidnotyieldaperfectlystableframerate.IdugalittlebitwithsomeofthetoolsandtechniquesIuseeverydayatworkandIwasabletoquicklyfindsomeofthereasonswhyFalconProdoesnotbehaveaswellasitcan.



Mygoalinthisarticleistoshowyouhowyoucantrackdownandfixperformanceissuesinanapplication,evenifyoudonthaveitssourcecode.AllyouneedisacopyofthelatestAndroid4.2SDKthenewADTbundlemakessetupabreeze.Iwouldhighlyrecommendyoudownloadtheapplicationtoapplythetechniquesdescribedhereonyourown.FalconProisunfortunatelyforyouapaidapplicationandIwillthereforeprovidelinkstovariousfilesyoucandownloadtofollowmyanalysis.

AwordaboutperformanceAndroid4.1putfocusonperformancewithProjectButteranditbroughtnewperformanceanalysistools,suchassystrace.Android4.2doesnotofferanythingassignificantassystracebutoffersacoupleofusefuladditiontoyourtoolbox.Youwilldiscoveroneofthesenewtoolslaterinthisarticle.

Performanceanalysisisoftenacomplextaskthatrequiresalotofexperienceandadeepknowledgeofonestools,hardware,APIs,etc.Itisexperiencethatallowedmetoperform



theanalysispresentedhereinonlyafewminutesyoucanseeithappeninrealtimeonmyTwitterstreamonDecember1st.Itwilllikelytakeyouafewtriesbeforeyoufeelateasewiththiskindofwork.

ConfirmingmysuspicionsOneofthemostimportantthingstorememberaboutperformanceworkistoalwaysusemeasurementstovalidateyouractions.EventhoughitseemedobvioustomethatFalconProwassufferingfromframeratedropsonaNexus4,Ineededtomakesure.IthereforeinstalledtheapplicationonaNexus7which,whilepowerful,offersadifferentperformanceprofilethanNexus4.Nexus7offersanotherinterestingadvantageforperformanceanalysisthatwelltalkaboutlater.

InstallingtheapplicationonNexus7didnotmakeadifferenceandIcouldstillseeframeratedrops.Itevenseemedslightlyworse.TomeasuretheproblemIdecidedtouseaProfileGPUrendering,atoolintroducedinAndroid4.1.YoucanfindthistoolintheDeveloperoptionssectionoftheSettingsapplication.

IfDeveloperoptionsisnotavailableonyourdevicerunningAndroid4.2,gototheAboutphoneorAbouttabletsectionandtaptheBuildnumberitematthebottom7times.



Withthisoptionturnedon,thesystemwillkeeptrackofthetimeittooktodrawthelast128framesofeverywindow.TousethistoolyoumustnowkillyourapplicationafutureversionofAndroidwillgetridofthisrequirement.

Methodology:unlessspecifiedotherwise,everymeasurementinthisanalysisisdonebyslowlyscrollingthemaintimelineupanddownbyafewpixelsatatime,revealingatmostoneextralistitem.

Afterlaunchingtheapplicationandscrollingthemaintimeline,Iranthefollowing



commandfromaterminal:

$adbshelldumpsysgfxinfocom.jv.falcon.pro

IntheresultinglogsyouwillfindasectionentitledProfiledatainms.Thissectioncontains,foreachwindowbelongingtotheapplication,atableof3columns.Tousethisdata,simplycopythetableinyourfavoritespreadsheetprogramandgenerateastackedcolumnschart.Thechartbelowistheresultofmymeasurement(theoriginalspreadsheetcanbeviewedonline.)

Eachcolumngivesanestimateofhowlongeachframetakestorender:

1. DrawisthetimespentbuildingdisplaylistsinJava.ItindicateshowmuchtimeisspentrunningmethodssuchasView.onDraw(Canvas).

2. ProcessisthetimespentbyAndroids2Drenderertoexecutethedisplaylists.ThemoreViewsinyourhierarchy,themoredrawingcommandsmustbeexecuted.

3. Executeisthetimeittooktosendaframetothecompositor.Thispartofthegraphisusuallysmall.

Reminder:torendersmoothlyat60fps,eachframemusttakelessthan16mstocomplete.

Timeinmsperframe

ExecuteProcessDraw

0

7

14

21

28



AboutExecute:ifExecutetakesalongtime,itmeansyouarerunningaheadofthegraphicspipeline.Androidcanhaveupto3buffersinflightandifyouneedanotheronetheapplicationwillblockuntiloneofthesebufferesisfreedup.Thiscanhappenfortworeasons.ThefirstoneisthatyourapplicationisquicktodrawontheDalviksidebutitsdisplayliststakealongtimetoexecuteontheGPU.Thesecondreasonisthatyourapplicationtookalongtimetoexecutethefirstfewframesoncethepipelineisfullitwillnotcatchupuntiltheanimationisdone.Thisissomethingwe'dliketoimproveinafutureversionofAndroid.

Thechartobviouslyconfirmsmysuspicions:whiletheapplicationmostlyperformswell,itsometimesdropsaframe.

TakingacloserlookEventhoughthedatawegatheredshowsthattheapplicationsometimestakestoolongtodraw,itdoesnttellthewholestory.Theframeratecanalsobeaffectedbyunscheduledormischeduledframes.Forinstance,ifanappalwaysdrawsinlessthan16msbutsometimesperformslongtasksbetweenframes,itwillsometimesmissaframe.

SystraceistheeasiesttooltocheckwhetherFalconProissufferingfromthisissue.Thistoolisasystemprofilerwithverylowoverhead.Itstimingsarereasonablyaccurateandgiveyouanoverviewofwhattheentiresystemisdoing,includingyourapplication.

Toenablesystrace,gotoDeveloperoptionsandselectEnabletraces.Adialogappears,lettingyouchoosewhattypeofeventsyouwanttoprofile.WeareonlyinterestedinGraphicsandView.

Note:donotforgettoturnoffProfileGPUrendering.



Tousesystrace,openaterminalandfromthedirectorytools/systraceintheAndroidSDK,runsystrace.py:



$./systrace.py

Bydefault,thetoolwillcaptureeventsfor5seconds.Isimplyscrolledthemaintimelineupanddown.TheresultingtraceisastandaloneHTMLdocument.

Tip:tonavigateasystracedocument,usetheWASDkeystopanandzoom.Wwillzoominonthemousecursor.

Asystracedocumentshowsalotofveryinterestinginformation.Forinstance,itshowsyouwhetheraprocessisscheduled,andonwhichCPU.Ifyouzoominonthelastrow,called10440:m.jv.falcon.proyoucanseewhattheapplicationwasdoing.IfyouclickononeoftheperformTraversalsblocksyoucanseehowlongtheapplicationspentdrawingaframe.

WhilemostoftheperformTraversalsarebelowthe16msthreshold,sometakemoretime,thusconfirmingthemeasurementspreviouslyobtained(zoominatthe935msmarkertoseesuchablock.)

Moreinterestingly,youcanseethattheapplicationsometimesmissesaframebecauseitdoesntmanagetoscheduleadrawoperation.Zoominatthe270msmarkertofindadeliverInputEventblocktaking25ms.Thisblocksindicatesthattheapplicationspent25msprocessingatouchevent.SincetheapplicationisusingaListView,thisislikelyduetoaproblemintheadapterbutwellgetbacktothislater.

Systracewasusefultonotonlyconfirmthattheapplicationisspendingtoomuchtimedrawing,butalsotohelpusfindanotherpotentialperformancebottleneck.Itisaveryusefultoolbutithasitslimitations.Itonlyprovideshighleveldataandwemustturntoothertoolstounderstandwhatistrulygoingon.

VisualizingoverdrawDrawingperformanceissuescanhavemanyrootcausesbutacommononeisoverdraw.Overdrawhappenseverytimetheapplicationasksthesystemtodrawsomethingontopofsomethingelse.Thinkaboutthesimplestapplicationpossible:awindowwithawhitebackgroundandasinglebuttonontopofit.Whenthesystemdrawsthebutton,itdrawsovertheexistingwhitebackground.Thatsoverdraw.

Overdrawisinevitablebuttoomuchoverdrawcanbeanissue.Deviceshavelimitedmemorybandwidthandifoverdrawcausesyourapplicationtorequiremorebandwidth



thanavailable,performancewilldegrade.Theamountofoverdrawyoucanreasonablyaffordvariesfromdevicetodevice.

Agoodruleofthumbistoaimforamaximumoverdrawof2xthismeansyoucandrawthescreenonce,thendrawtwiceagainontop,paintingeachpixel3timestotal.

Thepresenceofoverdrawalsousuallyindicatesotherproblems:toomanyviews,complexhierarchy,longerinflationtimes,etc.

Androidoffers3toolstohelpidentifyandfixoverdraw:HierarchyViewer,TracerforOpenGLandShowGPUoverdraw.ThefirsttwocanbefoundinADTorthestandalonemonitortool.ThelasttoolispartofDeveloperoptions.

ShowGPUoverdrawpaintsthescreenindifferentcolorstoindicatewhereoverdrawoccurs,andhowmuch.TurnitonnowanddontforgettokillyourapplicationafutureversionofAndroidwillremovethisrequirement.



BeforewelookatFalconPro,letsseewhattheSettingsapplicationlookslikewithShowGPUoverdrawturnedon.



Itiseasytointerprettheresultsifyourememberthemeaningofeachcolor:

Nocolormeansthereisnooverdraw.Thepixelwaspaintedonlyonce.Inthisexample,



youcanseethatthebackgroundisintact.

Blueindicatesanoverdrawof1x.Thepixelwaspaintedtwice.Largeblueareasareacceptable(iftheentirewindowisblue,youcangetridofonelayer.)

Greenindicatesanoverdrawof2x.Thepixelwaspaintedthreetimes.Mediumsizedgreenareasareacceptablebutyoushouldtrytooptimizethemaway.

Lightredindicatesanoverdrawof3x.Thepixelwaspaintedfourtimes.Smalllightredareasareacceptable.

Darkredindicatesanoverdrawof4xormore.Thepixelwaspainted5timesormore.Thisiswrong.Fixit.

BasedonthisinformationyoucanseethatSettingsisawellbehavedapplicationthatdoesnotrequireanyextrawork.Thereisalittlebitofredintheswitchesbutnothingworthourefforts.

Transparentpixels:lookcloselyatthepreviousscreenshots.Eachiconispaintedblue.Youcanseethatthetransparentpixelsofthebitmapscountagainstyouroverdraw.TransparentpixelsmustbeprocessedbytheGPUandcanbeexpensive.Androidusesoptimizationstoavoiddrawingtransparentpixelsinlayersand9patchessoyoushouldonlyworryaboutbitmaps.

OverdrawandtheGPU:therearetwotypeofmobileGPUarchitectures.Thefirstusesdeferredrendering,forinstanceImaginationTech'sSGXseries.ThisarchitectureallowstheGPUtodetectandfixoverdrawinspecificsituations(itdoesn'tworkifyouareblendingtransparentortranslucentpixels.)ThesecondarchitectureusesimmediaterenderingandcanbefoundinNVIDIA'sTegraGPUs.Thisarchitecturecannotoptimizeoverdrawforyou,whichiswhyIliketotestonNexus7.Therearemanyadvantagesanddisadvantagestobotharchitecturesbutit'sbeyondthescopeofthisarticle.Justknowthatbothworkreallywell.

LetsnowtakealookatFalconPro



Thereisalotofredinthatscreenshot!Whatisinterestinghoweveristhatthelistbackgroundisgreen.Thisshowstheresa2xoverdrawbeforetheapplicationevenstartsdrawingitscontent.Theproblemweseehereismostlikelyrelatedtohavingseveralfullscreenbackgrounds.Itisusuallytrivialtofix.

RemovingextraneouslayersToreduceoverdrawwemustfirstunderstandwhereitscomingfrom.ThisiswhereHierarchyViewerandTracerforOpenGLbeforeuseful.HierarchyViewerispartofADT(ormonitor)andcanbeusedtoinspectasnapshotoftheViewhierarchy.Itisespeciallyusefultodebuglayoutissuesbutcomesinhandyforperformanceworkaswell.

Important:HierarchyViewerwillonlyworkonnonsecuredevicesbydefault,suchasengineeringphonesandtabletsortheemulator.TouseHierarchyVieweronanyphoneaddViewServer,anOpenSourcelibrary,toyourapplication.

OpentheHierarchyViewerperspectiveinADT(ormonitor),thenselecttheWindowstab.Thewindowhighlightedinboldistheforegroundwindowonthedeviceandusuallytheoneyouwanttoinspect.ClickonitthenclicktheLoadbuttoninthetoolbar(itlookslikeatreeofbluesquares.)Loadingthetreecantakeawhilesobepatient.Whenthetreeisreadyyoushouldseesomethingsimilartothepicturebelow.



NowthattheViewhierarchyisloadedinthetoolwecanexportitasaPhotoshopdocument.Todoso,clickthesecondbuttoninthetoolbarthetooltipsaysCapturethewindowlayers[].AdobePhotoshopitselfisnotrequiredasthegenerateddocumentiscompatiblewithtoolssuchasPixelmator,TheGIMP,etc.ThePSDfileIgeneratedisavailablefordownload.

ThePhotoshopdocumentshowsonelayerperViewintheapplication.Eachlayerismarkedvisibleorinvisible,basedonthereturnvalueofView.getVisibility().EachlayerisnamedafteritsView,usingeithertheViewandroid:idifavailableoritsclassname.IoncestartedaddingsupportforgroupstorecreatetheViewtreeIshouldreallyfinishthisfeature.



Byinspectingthelistoflayers,wecanquicklyidentifyatleastonesourceofoverdraw:multiplefullscreenbackgrounds.Thefirstoneisthefirstlayer,calledDecorView.ThisviewisgeneratedbyAndroidandcontainsthebackgroundspecifiedinthetheme.Thisdefaultgradientisinvisibleintheapplicationsoitcanbesafelyremoved.

ScrollingupfromDecorViewyoucanseeaLinearLayoutcontaininganotherfullscreengradientbackground.ThisisthesameexactbackgroundasDecorViewsanditisthereforeunnecessary.TheonlyvisiblebackgroundthatmustremainbelongstotheViewcalledid/tweet_list_container.

Removingthewindowbackground:thebackgrounddefinedinyourthemeisusedbythesystemtocreatepreviewwindowswhenlaunchingyourapplication.Neversetittonullunlessyourapplicationistransparent.Instead,setittothecolor/imageyouwantorgetridoffromonCreate()bycallinggetWindow().setBackgroundDrawable(null).



FurtherreducingoverdrawThePhotoshopdocumentisusefultounderstandhowtheapplicationisbuiltbutitisalittlebitdifficulttousetogetridofsmalleroverdrawregions.WemustnowturntoTracerforOpenGL.OpentheperspectiveofthesamenameinADT(ormonitor)andclickthearrowiconinthetoolbar.EnterthepackagenameofyourappandthenameofthemainActivity,thenselectadestinationfileandclickTrace.

Wordofadvice:OpenGLtracescanbehugeandreallyslowtocapture.Tomakethemsmallerandcapturefaster,uncheckalltheDataCollectionOoptionsboxes.

Activityname:logcatwillshowthenameofthepackageandActivitywhenyoulaunchanapplication.ThisishowIknowwhattotypeinTracerforOpenGL.

Whentheapplicationisupandrunning,turnonthefirsttwooptions:

CollectFramebuffercontentsoneglSwapBuffers()



CollectFramebuffercontentsonglDraw*()

Thefirstoptionisusefultoquicklyfindtheframeyoureinterestedinwhilethesecondoptionallowsustoseeeachframebeingbuiltdrawingcommandbydrawingcommand.Thissecondoptioniskeytosolvingoverdrawproblems.

WiththesetwooptionsenabledIstartedscrollingthemaintimeline.Itwillnowtakealongtimetocaptureeachframe(30secondsisnotunexpected)soIrecommendyousimplydownloadthetraceIcaptured.YoucanopenthistracefileinTracerforOpenGLbyclickingthefirstbuttoninthetoolbar.

Onceloaded,atraceshowsyoueachGLcommandsenttotheGPUforeverycapturedframe.Ifyoudownloadedmytracefile,skiptoframe21.WhenaframeisselectedyoucanseewhatitlookslikeintheFrameSummarytab.Inaddition,youcanclickondrawingcommands,highlightedinblue,toseethecurrentstateoftheframeintheDetailstab.



Organization:theGLcommandsaregroupedbyView.TheyrecreatethesametreeyoucanseeinHierarchyVieweroryourXMLlayoutfiles.ThismakesitveryeasytounderstandwhatViewgeneratedaspecificoperation.

Byclickingsuccessivelyonthefirst3drawingcommandsyoucanseetheproblemalreadyidentifiedinPhotoshopafullscreenbackgroundisdrawn3times.

Wecanfindmoretooptimizebylookingfurtherdownthetrace.Whenatweet(listitem)isdrawn,anImageViewisusedtodrawtheavatar.TheImageViewfirstdrawsabackgroundthentheavataritself:



Ifyoulookcloselyyouwillnoticethatthebackgroundisonlyusedasaborderfortheimage.Thismeansthedarkpartinthecenteroftheavatarbackgroundcreatesoverdraw.Thatpieceofthe9patchisentirelycoveredbytheavatar.

Averysimplefixforthisproblemistomakethestretchablecenterpieceofthe9patchtransparent.Androids2Drendereroptimizesawaytransparentpiecesin9patches.Thissimplechangewillgetridofabitofoverdraw.

Interestingly,thesameexactproblemoccurswithinlinemedia.Avatarsaresmallsotheiroverdrawisnotabigdeal,butinlinemediacanoccupylargeareasofthescreen.Thefixisexactlythesame.



Futureoptimization:IwouldlikeAndroid's2Drenderingpipelinetobeabletoautomaticallydetectandcorrectoverdrawforyou.WehaveafewideasbutIcannotmakeanypromise.JustaswithbuiltinGPUoptimizations,thiswouldonlyworkwithfullyopaqueprimitives.

FlatteningtheviewhierarchyNowthatoverdrawis(mostly)takencareof,letsgobacktoHierarchyViewer.Byinspectingthetreewecantrytoidentifyunnecessaryviews.Removingviews,especiallyViewGroups,cannotonlyhelpimproveframeratebutalsomemoryconsumption,startuptime,etc.

AquicklookatFalconProsviewhierarchyisenoughtoidentifyseveralViewGroupswithasinglechild.TheseViewGroupsareoftenunnecessaryandeasytoremove.Atleasttwoofthenodesshowninthescreenshotbelowshouldberemoved.

Therearenumerousotherviewsthatcanberemovedfromthistree.Forinstance,eachtweetcontainsaRelativeLayoutcalledid/listElementBottom.Thislayoutcontainsthe



nameoftheauthor,hisTwitterhandle,thetimeelapsedsincethetweetwaspostedandanicon.ThenameandthehandlearetwoseparateTextViewinsteadofbeingjustonewithspanstousedifferentstyles.ThetimeandtheiconuseaTextViewandanImageViewthatcouldbecombinedinasingleTextView,usingTextViewscompounddrawables.

TheslideinmenuontheleftusesseveralgroupsofLinearLayout+TextView+ImageViewtodisplaylabelswithicons.EachoneofthesegroupscanbereplacedbyasingleTextView.

HowtoflattenyourUI:Iexplainthesetechniquesinmoredetailinmy2009GoogleI/OtalkentitledTurbochargeyourUI.

Whataboutinputevents?Rememberwhenwelookedatsystraceandfoundoutthattoucheventshandlingwassometimesslow?Itsnowtimetoaddressthisissueandthebesttoolatourdisposaltounderstandmoreaboutwhattheapplicationisdoingistraceview.

TraceviewisaDalvikprofilerwhichmeasureshowmuchtimetheapplicationspendscallingmethods.Toinvokeit,opentheDDMSperspectiveinADTormonitor,selectyourapplicationprocessintheDevicestab,thenclicktheStartmethodprofilingbutton(threearrowswitharedcircle.)

Afterenablingtracing,Iscrolledthemaintimelineupanddownandclickedthebuttonagaintofinishthetrace.Youcanalsodownloadmyowntrace.Theresultlookslikethescreenshotbelow.



Clickingonitem#21,ViewRootImpl.draw(),highlightsthetimespentdrawing.Thelastcolumnofthetablegivesyouanideaoftheaveragetimespentinthismethodandallitschildren.Ifyoulookcloselyatthetimeline,withthehighlights,youwillnoticegapsbetweensuccessiveframes.

Aneasywaytofigureoutwhatsgoinginduringthesegapsistozoominatthebeginningofonethemandclickthelargestcoloredblockyoucanfind.Youcanthenfollowtheparentchainuntilyoufindsomethingyourecognize.Inmycase,IfollowedacalltoPattern.compileImpl,takinganaverageof0.5ms,allthewayuptoDBListAdapter.bindView.

Obviouslytheapplicationrecompilesthesameregularexpressionoverandoveragain,everytimeanewitemisboundwhilescrollingthemaintimeline.TraceviewshowsthatbindViewtakes38msonaverageand56%ofthattimeisspentparsingHTMLtext.This



seemslikesomethingthatcouldbeachievedinthebackgroundinsteadofblockingtheUIthread.andofcourse,theregexshouldnotberecompiledeverytime.

Itsyourturn!Ikeptonelasttraceasanexercise.Theapplicationhastwoslideinmenusthatcanbeunveiledbyswipingthetimelineleftorright.ShowGPUoverdrawshighlightsanexcessiveamountofdrawingduringtheswipesandIusedTracerforOpenGLtocaptureseveralframesofaswipe.Downloadmytraceandseeifyoucanfigureoutwhatscausingtheoverdraw(gotoframe#34.)

Hints:theapplicationshouldusehardwarelayersbycallingView.setLayerType()tosimplifydrawing.Therearealsoextraneousbackgroundsthatcanbeoptimizedawaywithcleveruseof9patches.Clippingcouldalsobeveryhelpful.Finally,maybeaColorFiltersetonaPaintpassedtosetLayerType()couldhelpremovethelastdrawingcommand.

Ishowedyouvarioustoolsyoucanusetooptimizeyourapplications.Icouldspendalotoftimedescribingwhattechniquestousetosolveissuesidentifiedwiththesetoolsbutthisarticlewouldturnintoabook.CheckoutthereferencedocumentationoftheofficialAndroiddeveloperswebsiteandalltheGoogleI/OAndroidtalks(slidesandvideosareavailableonlineforfree.)

RomainGuywww.curiouscreature.org

Documents

Android Performance Case Study, Falcon Pro