Effec%ve Soware · 2018. 2. 8. · 6th March 2017 ESW – Lecture 3 3 JAVA Versions » first release 1996 by Sun Microsystems (later Oracle) » many different implementaons (GNU,

David Šišlák [email protected]

Effec%veSo*ware

Lecture3:Virtualmachine,byte-code,(de-)compilers,disassembler,profiling

6thMarch2017 ESW–Lecture3 2

Introduc%on–VirtualMachine

»  VirtualmachineexecuHonmodel•  sourcecode•  compiledVMbyte-code•  hybridrun-Hmeenvironment(plaJormdependentVMimpl.)

–  interpretedbyte-code–  compliedassembly-code(naHveCPUcode)–  automatedplaJormcapabilityopHmizaHons(e.g.useofSIMD)

»  byte-codevs.assembly-code•  (+)plaJormindependence(portable)–architecture(RISC/CISC,bits),OS•  (+)reflecHon–observe,modifyownstructureatrun-Hme•  (+)smallsize•  (-)slowerexecuHon–interpretedmode,compilaHonlatencies


JAVAVersions

»  firstrelease1996bySunMicrosystems(laterOracle)»  manydifferentimplementaHons(GNU,IBM,etc.)

»  languagechangesandimprovements•  1.4(2002)–assert,NIO•  5.0(2004)–generics,annotaHons,auto-boxing,enum,concurrency

uHls,varargs,foreach,profilingAPI•  6(2005)–basicjavascriptsupport,performanceandGC

improvements(G1,compressedpointers),compilerAPI•  7(2011)–invokedynamic,switchstrings,auto-closeable,GPUpipeline

API•  8(2014)–lambda,streams,improvedjavascriptsupport(baseon

invokedynamic),removedpermgen(metaspace/naHvemem.isused)•  9(2017?)–Ahead-of-TimeCompila6on(non-6eredvs.6eredAOT)

non-6eredAOTprovidepredictableperformance


Execu%onTimeComparison

»  TheComputerLanguageBenchmarksGame (hBp://benchmarksgame.alioth.debian.org/)

•  10differentalgs.(e.g.DNAmanipulaHon)


JAVAVirtualMachine–MemoryLayout


JAVAVirtualMachine–MethodArea

»  methodareasharedamongallthreads»  classdefiniHons

»  run-Hmeconstantpool»  fieldandmethoddata»  byte-codeformethodsandconstructors»  iniHalizaHonmethods(<clinit>,<init>)

»  naHvemethod»  implementaHonofnaHvemethods


JAVAVirtualMachine-Frame

»  frame»  eachthreadhasstackwithframes(outsideofheap,fixedlength)

StackOverflowErrorvs.OutOfMemoryError»  frameiscreatedeachHmemethodisinvoked(destroyedaeerreturn)»  framesizedeterminedatcompile-Hme(inclassfile)»  variables(long,doubleintwo)

»  {this}–instancecallonly!»  {methodparameters}»  {localvariables}

»  operandstack(anytype)»  LIFO

»  referencetorun-%meconstantpool(classdef)»  method+classisassociated


JAVAVirtualMachine–Stack-orientedBytecode

»  stack-oriented-stackmachinemodelforpassingparametersandoutput

(2+3)×11+1


JAVAVirtualMachine–Opcodes

»  opcode(1byte+variousparameters):»  loadandstore(aload_0,istore,aconst_null,…)»  arithmeHcandlogic(ladd,fcmpl,…)»  typeconversion(i2b,d2i,…)»  objectmanipulaHon(new,puJield,geJield,…)»  stackmanagement(swap,dup2,…)»  controltransfer(ifeq,goto,…)»  methodinvocaHon(invokespecial,areturn,…)–framemanipulaHon»  excepHonsandmonitorconcurrency(athrow,monitorenter,…)

»  prefix/suffix–i,l,s,b,c,f,danda(reference)»  variablesasregisters–e.g.istore_1(variable0isthisforinstancemethod)

VS.


JAVAVirtualMachine

»  usedtoimplementalsootherlanguagesthanJAVA»  Erlang->Erjang»  JavaScript->Rhino»  Python->Jython»  Ruby->Jruby»  Scala,Clojure–funcHonalprogramming»  others

»  byte-codeisverifiedbeforeexecuted:»  branches(jumps)arealwaystovalidlocaHons–onlywithinmethod»  anyinstrucHonoperatesonafixedstacklocaHon(helpsJITfor

registersmapping)»  dataisalwaysiniHalizedandreferencesarealwaystype-safe»  accesstoprivate,packageiscontrolled


JAVAVirtualMachine–Example1–SourceCode


JAVAVirtualMachine–ClassFileStructure


JAVAVirtualMachine–Example1–ClassFile


JAVAVirtualMachine–Example1–DisassembledConstants

»  javap–JAVAdisassemblerincludedinJDK


JAVAVirtualMachine–Example1–DisassembledFields


JAVAVirtualMachine–Example1–DisassembledMethod

»  geJield•  takes1reffromstack•  buildanindexintorunHmepoolofclassinstancebyreferencethis

»  areturn•  takes1reffromstack•  pushontothestackofcallingmethod


JAVAVirtualMachine–Example1–DisassembledConstructor


JAVAVirtualMachine–Example1–Decompiler

»  procyon–open-sourceJAVAdecompiler,supportJAVA8


JAVAVirtualMachine–Example2–SwitchSourceCode


JAVAVirtualMachine–Example2–SwitchBytecode


JAVAVirtualMachine–Example2–SwitchBytecode


JAVAVirtualMachine–Example2–CycleBytecode


JAVAVirtualMachine–SourceCodeCompila%on

»  sourcecodecompila%on(Source->Bytecode)»  bytecodeisnotbeqerthanyoursourcecode

»  invariantsinlooparenotremoved»  noopHmizaHonslike

»  loopunrolling»  algebraicsimplificaHon»  strengthreducHon

»  opHonalexternalobfuscatorbytecodeopHmizaHons-ProGuard•  shrinker–compactcode,removedeadcode•  opHmizer

–  modifyaccesspaqern(private,staHc,final)–  inlinebytecode

•  obfuscator–renaming,layoutchanges•  preverifier–ensureclassloading

Test yourself


JAVAVirtualMachine–BytecodeCompila%on

»  Just-in-%me(JIT)»  convertsbytecodeintoassemblycodeinrun-Hme»  lookOpenJDKsourcesforverydetailedinformaHon

»  adap%veop%miza%on(HeredcompilaHon)»  balancetrade-offbetweenJITandinterpreHnginstrucHons»  monitorsfrequentlyexecutedparts“hotspots”includingdataon

caller-calleerelaHonshipforvirtualmethodinvocaHon»  triggersdynamicre-compilaHonbasedoncurrentexecuHonprofile»  inlineexpansiontoremovecontextswitching»  opHmizebranches»  canmakeriskyassumpHon(e.g.skipcode)->

»  unwindtovalidstate»  deopHmizepreviouslyJITedcodeevenifcodeisalreadyexecuted


JAVAVirtualMachine–JITCompila%on

»  Just-in-Hme(JIT)–usuallyasynchronous(3C1,7C2threadsfor32cores)»  C1(client)–muchfasterthanC2

»  simplifiedinlining,usingCPUregistry»  window-basedopHmizaHonoversmallsetofinstrucHons»  intrinsicfuncHonswithvectoroperaHons(Math,arraycopy,…)

»  C2(server,d64)–high-endfullyopHmizingcompiler»  deadcodeeliminaHon,loopunrolling,loopinvarianthoisHng,commonsub-expressioneliminaHon,constantpropagaHon

»  fullinlining,fulldeopHmizaHon(backtolevel0)»  escapeanalysis,nullcheckeliminaHon,»  paqern-basedloopvectorizaHonandsuperwordpacking(SIMD)

»  %eredcompila%on–hybridadapHng(sinceJVM7,defaultinJVM8)»  on-stackreplacement(OSR)–opHmizaHonduringexecuHon

»  startatbytecodejumptargets(goto,if_)


AssemblyCode

»  reasonstostudyassemblycode(bothJavaandC/C++)•  educaHonalreasons

–  predictefficientcodingtechniques•  debuggingandverificaHon

–  howwellthecodelookslike•  opHmizecode

–  forspeed•  avoidpoorlycompiledpaqerns•  datafitsintocache•  predictablebranchesornobranches•  usevectorprogramingifpossible(SIMD)

»  256bitregisterswithAVX2sinceIntelSandyBridge»  512bitAVX-512sinceIntelKnightLanding(XeonPhi)

–  forsize•  primarilycodecacheefficiency


JAVAVirtualMachine–Example2–TieredCompila%on

»  -XX:+PrintCompilaHon(-XX:+PrintInlining)


JVM–Example2–daysInMonthAssemblyCode–Tier3

»  -XX:+UnlockDiagnosHcVMOpHons-XX:+PrintAssembly»  allexamplesareinJVM864-bitServer,IntelHaswellCPU,AT&Tsyntax%er3-C1withinvoca%on&backedgecounters+MethodDataOopcounter

because:count="256"iicount="256”hot_count="256”stackiniHalizaHon,invoca%oncounterinMDO(0xDC)+triggerC2

0x1ff8 >> 3 = 1024 invocations trigger tier 4 (C2)

month, year stacking banging technique, stack allocation, saving registers



ESI is month input

default jump



targetformonth=4,backedgecountertrackinginMDO(0x290):jumptarget,inlinedTLABalloca%onofIntegerobject:

no space in TLAB -> new TLAB + external allocation with header init returns after the inlined allocation

EBX=30 is retVal

RAX Integer instance address Object structure (64-bit JVM): -  header 12 or 16 Bytes -  object data super class first, type grouped

8B - mark word

4B / 8B – Klass ref.

… object data

Array object structure (64-bit JVM): -  header 16 or 20 Bytes -  sequence of array values

8B - mark word

4B / 8B – Klass ref.

sequence of values

4B – array length

0x10 Integer instance size

object initialization, header filed with prototype mark



inlinedIntegerconstructorwithsupers,invocaHoncountsinMDOs(0xDC) Integer::<init>,Number::<init>,Object::<init>

-currentlyinHer3(C1countersinMDO) invocation cnt of Integer::<init> in daysInMonth for inline

invocation cnt in Integer::<init> + trigger its C2

invocation cnt of Number::<init> in Int::<init> for inline

invocation cnt in Number::<init> + trigger its C2

invocation cnt of Object::<init> in Numb::<init> for inline

invocation cnt in Object::<init> + trigger its C2

RAX.value = EBX (retVal)



finalcleanupandreturn,RAXcontainsreturnvalue(pointertoIntegerinstance)»  safepoint–OopsinperfectlydescribedstatebyOopMap(GCmaps)

•  threadsaresuspended,Oopsafelymanipulatedexternallyandresumedaeer•  ininterpretedmode–betweenany2bytecodes•  inC1/C2compiled–endofallmethods(notin-lined),non-countedloopbackedge,

duringJVMrun-Hmecall•  parked,blockedonIO,monitororlock•  whilerunningJNI(donotneedthreadsuspension)•  globalsafepoint(allthreads)–stoptheworld

–  GC,printthreads,threaddumps,heapdump,getallstacktrace–  enableBiasedLocking,RevokeBias–  classredefiniHon(e.g.instrumentaHon),debug

•  localsafepoint(justexecu%ngthread)–  de-opHmizaHon,enable/revokebiaslocking,OSR

stack dealocation, reload register safepoint poll check


JVM–TimeToSafePoint(TTSP)

-XX:+PrintSafepointStaHsHcs-XX:+PrintGCApplicaHonStoppedTime-XX:PrintSafepointStaHsHcsCount=1

GetStackTraceoverheads:



%er4–C2–noprofilecountersbecause:count="5376"iicount="5376”hot_count="5376”

stackiniHalizaHon,uselookuptablejumpfortableswitch

default (>=12)

month, year



targetformonth=4Integer.<init>,Number.<init>,Object.<init>-iicount=“5376”->Inline(hot)op%mizedbranching,inlinedTLABalloca%on,inlinedconstructors,nonulling,cachingop%miza%on

EBP=30 is retVal

TLAB Integer object allocation, ref in RAX

MarkWord fetch from class and then store compressed OOP to Integer class

RAX.value = EBX (retVal)

final cleanup

RAX contains return value (pointer to Integer instance)



targetfordefaultclassIllegalArgumentExcepHonnoprofile->uncommon->reinterpretremapinputs,returnbacktoreinterpreterthendiscardHer3version


JVM–Example2–computeAssemblyCode–Tier4OSR

OSR@10–OnStackReplacementatbytecode10%er4–C2(beforetherewasHer3OSR@10because60416loopsandHer3)

because:backedge_count=”101376"hot_count=”101376”copy4localsonstackfromHer3OSR@10toregs

RSI compiled stack of tier 3 OSR @10


JVM–Example2–computeAssemblyCode–Tier4OSR

loopcriteriathenthereisinlinedHer4daysOfMonth(lookupjump)becausethecallishotendingwithaddiHonintoaccumulatororeinterpretonendofcyclejump(unstableif_bytecode),save3localstostack

EBX is local I; 0xF4240 = 1_000_000


JVM–Example2–computeAssemblyCode–Tier4

%er4–C2because:count=”2”backedge_count=”150528”

usecombinaHonoffullinline,deadcodeelimina%on,objectescape,loopinvarianthois%ng,strengthreduc%on

30_000_000

RAX contains return value (primitive int)


JavaVirtualMachine–Performance32vs64-bit

»  requireswarm-uptou%lizebenefitsofC2(orC1)»  compilerscannotdoallmagic->writebekeralgorithms

»  32-bitvs64bitsJVMs•  32-bit(max~3GBheap)

–  smallermemoryfootprint–  slowerlong&doubleoperaHons

•  64-bitmax32GBvirtualmemory(withdefaultObjectAlignmentInBytes)-  fasterperformanceforlong&double–  slightincreaseofmemoryfootprint–  compressedOOPsareslightlyslowerforreferencesuponusage–  compressedOOPslessmemory->lessfrequentGC->fasterprogram

•  64-bit>32GBvirtualmemory(largeheap)–  fastreferenceusage–  wasHngalotofmemory(48GB~32GBwithcompressedOOPs)


JavaVirtualMachine–CPUandMemoryProfiling

»  jvisualvm•  JVMmonitoring,troubleshooHngandprofilingtool•  includedinallJDKs•  profiledthreadlimit32

»  profiling•  CPU–Hmespentinmethods•  memory–usage,allocaHons

»  modes•  sampling

–  periodicsamplingofstacksofrunningthreadstoesHmateslowest–  noinvocaHoncounts,no100%accuracy(varioussamplingerrors)–  nobytecode(&assemblycode)modificaHons–  1-2%impacttostandardperformance

•  tracing(instrumetaHon)–  instrumentedbytecode->affectedperformance->affectedcompilerop%miza%ons


JVM–Example2–CPUTracingofdaysOfMonth

assemblycodeof%er4–C2(beforetherewasverycomplexHer3)inlineddaysInMonthrootMethodEntrytracking

749 Bytes of assembly code for each rootMethodEntry


JVM–Example2–CPUTracingofdaysOfMonth

addiHonalrootMethodEntryandrootMethodExittrackingsforInteger::<init>andNumber::<init>

inlinedrootMethodExitaeerIntegerinstance.value=retVal

313 Bytes of assembly code for each rootMethodEntry


JVM–Example2–CPUTracingOutcome


JVM–Example2–ProfilingPerformance

»  CPUtracingofcomputeresultsintomuchslowercode•  noobjectescapefromdaysInMonthcall•  noinvarianthoisHng•  nostrengthreducHon(fullloopremainsthere)

»  objectallocaHonissimilarwithtraceObjAllocinjectedcalls

»  recommendedapproach•  dosamplingfirst•  idenHfyperformanceboqlenecks(wheremostHmeisspent)

–  itcouldbeoutsideofJVM(e.g.latencyofexternalDB,filesystem)•  focuswithtracingjusttoidenHfiedparts


JVM–JavaMissionControl

jmc–JRockitJVM,includedincommercialJDKs,samplinginFlightrecorder


ApproachtoPerformanceTes%ng

»  testrealapplica%on–ideallythewayitisused•  microbenchmarks–measureverysmallunits

–  warm-up–tomeasurerealcode,notcompilersitself,biasedlocks•  keepinmindcaching

–  bewareofcompilers–useresults,reorderingofoperaHons–  synchronizaHon–mulH-threadedbenchmarks–  varypre-calculatedrightparametersaffecHngcomplexity–differentopHmizaHoninreality

•  macrobenchmarks–measureapplicaHoninput/output–  leastperformingcomponentaffectsthewholeapplicaHon

•  mesobenchmarks–isolaHngperformanceatmodularlevel»  understandthroughput,elapsedandresponse%me

•  outlierscanoccur–e.g.GC•  useexisHnggeneratorsthanwriHngown


ApproachtoPerformanceTes%ng

»  understandvariability–changesoverHme•  internalstate•  backgroundeffects–load,network•  probabilisHcanalysis–workswithuncertainty

»  testearly,testo*en–ideallypartofdevelopmentcycle•  ideallysomeproperlyrepeatedmesobenchmarking•  automatetests–scripted•  propertestcoverageoffuncHonalityandinputs•  testontargetsystem–differentcodeondifferentsystems

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Effec%ve Soware · 2018. 2. 8. · 6th March 2017 ESW – Lecture 3 3 JAVA Versions » first release 1996 by Sun Microsystems (later Oracle) » many different implementaons (GNU,