Memory Allocation and Access Patterns in Dynamic ... - STUPS Group

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1 INTRODUCTION 21 IntroductionOver the last years dynamic programming languages like Javascript, Python or Ruby havegained more and more attention. Reasons for the increased popularity are for examplethe dynamic typing of objects and the automatic memory management which comes withmost languages. These can speed up the development of software considerably. However,these benefits don’t come for free as they incur a certain overhead and deny severalstatic optimizations that are possible in other languages like Java or C. Therefore otheroptimizations have been introduced to minimize this overhead.One of these optimizations which is used by some virtual machines (VMs) is integer taggingthat tries to avoid boxing of integers. Boxing of primitive data-types is needed indynamic languages, since the type of an object must be determinable during runtime.Although used by several VMs, the influence of integer tagging on performance has notbeen evaluated in detail so far.The aim of this thesis is to analyse the performance impacts gained by integer taggingfor interpreters. Therefore an existing Smalltalk VM is extended by integer tagging andthe performance for different configurations of this VM is measured using benchmarks.The evaluation of the results is focused on interpreters, as VMs using just-in-time (JIT)compilation have different trade-offs.The implementation of integer tagging is described in Section 3. The idea of integercaching, an alternative optimization to reduce the memory footprint, and its implementationis described in Section 4. Section 5 describes some important additional optimizationsand modifications implemented for the SOM++ virtual machine. The performance of integertagging is then evaluated in Section 6. First the benchmarks and their characteristicsof integer usage are described. Then the benchmark results are evaluated. This sectionends with an short evaluation of integer caching and of integer tagging on x86 64 andARM based systems. Section 7 lists related research done on integer tagging. FinallySection 8 concludes this thesis.
2 BACKGROUND 32 Background2.1 SmalltalkSmalltalk is a dynamically typed, purely object-oriented programming language and afull development environment at the same time. It was created by the Learning ResearchGroup at Xerox PARC during the 1970s and made publicly available as Smalltalk-80 [1]in 1982.Smalltalk influenced a lot of other programming languages like Java, Objective-C andPython as well as Windows or Macintosh with its windowing system. Some of its keyconcepts are:• everything is an object (including integers, strings, bools and methods)• everything happens by sending messages• single inheritance• you can change everything, even running programsMajor Smalltalk implementations nowadays are Pharo 1 , Squeak 2 , Cincom Smalltalk 3 andGNU Smalltalk 4 . Figure 1 shows Pharo Smalltalk running unit tests.2.2 SOMIn this thesis the SOM++ virtual machine is used as basis. It is implemented in C++ [2]and part of the SOM (Simple Object Machine) virtual machine family [3], which all hostthe same Smalltalk dialect but are implemented in different languages. It was developedat the University of Århus and the Hasso-Plattner-Institute 5 in Potsdam with focus oneducation and research. Therefore their architecture and implementation were kept simple,which eases modifications to the VM and evaluation of their effects. SOM’s instructionset architecture for example consists of 16 bytecode instructions only, which are executedby a simple bytecode-interpreter [4].For the author’s bachelor thesis [5] SOM++, originally using a mark-sweep garbage collector,was extended by a copying and a generational garbage collector. The garbage collectorimplementation used can be chosen by setting compile-switches. The implementation andkey advantages/ disadvantages are explained briefly.mark-sweep garbage collector SOM++ uses a pretty straightforward implementationof the mark-sweep algorithm [6]. Allocation of objects is simply handed over tostdlib’s malloc. Reclamation of garbage is achieved in two steps. First all live objects1 http://www.pharo-project.org2 http://squeak.org3 http://www.cincomsmalltalk.com4 http://smalltalk.gnu.org5 http://hpi.uni-potsdam.de/hirschfeld/projects/som/
Page 1: INSTITUT FÜRINFORMATIKSoftwaretech
Page 4 and 5: AbstractInteger tagging is an optim
Page 8 and 9: 2 BACKGROUND 4Figure 1: Pharo Small
Page 10 and 11: 2 BACKGROUND 6Point...pos_xpos_y...
Page 12 and 13: 2 BACKGROUND 8010000000000100100100
Page 14 and 15: 3 TAGGING IMPLEMENTATION 103 Taggin
Page 16 and 17: 4 IMPLEMENTATION OF INTEGER CACHING
Page 18 and 19: 5 GENERAL OPTIMIZATIONS AND MODIFIC
Page 20 and 21: 6 EVALUATION 166 EvaluationIn order
Page 22 and 23: 6 EVALUATION 183.5e+06Allocation St
Page 24 and 25: 6 EVALUATION 20Figure 15: Histogram
Page 26 and 27: 6 EVALUATION 22800000700000Types of
Page 28 and 29: 6 EVALUATION 246.3 Evaluation of Be
Page 30 and 31: 6 EVALUATION 26is barely visible as
Page 32 and 33: 6 EVALUATION 28300Garbage collectio
Page 34 and 35: 6 EVALUATION 30the copying collecte
Page 36 and 37: 6 EVALUATION 3245004000SOM++ mark s
Page 38 and 39: 6 EVALUATION 342500SOM++ generation
Page 40 and 41: 6 EVALUATION 36Average execution ti
Page 42 and 43: 6 EVALUATION 38Average execution ti
Page 44 and 45: 8 CONCLUSION 408 ConclusionDuring t
Page 46 and 47: BIBLIOGRAPHY 42[16] Michael Haupt,
Page 48: LIST OF FIGURES 4431 SOM benchmarks

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