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Workerthread 1Workerthread 2Workerthread 3Workerthread 41.11.2 1.3 1.41.51.62.32.42.12.23.13.23.43.53.3TimeFigure 4.4: Execution plan for TM-style speculation: each block A.B stands forthe B th iteration in the A th loop invocation: iteration 2.1 overlaps with iterations2.2, 2.3, 2.4, 2.7, 2.8, thus its memory accesses need to be compared with theirs even thoughall these iterations come from the same loop invocation and are guaranteed to be independent.erty of each loop invocation while still allowing threads to execute past the barrier withoutstalling. Since all existing speculative barrier synchronization techniques [30, 40, 45] requirespecialized hardware support, we refer to these techniques collectively as hardwarebasedbarrier speculation (HWBS).The work of Martínez et al. [40] is representative of the HWBS techniques. In thiswork, all worker threads start executing non-speculatively and are allowed to update theshared memory concurrently. A worker thread becomes speculative once it exceeds thebarrier boundary while other worker threads are still executing before the barrier. Whena worker thread becomes speculative, it first executes a checkpoint instruction to back up54
the architectural register values. During the speculative execution, values updated by thespeculative thread are buffered in the cache and corresponding cache lines are marked asspeculative. Later, access to a speculative cache line by other threads will trigger an accessconflict. When that happens, the speculatively executing thread is squashed and resteeredto the checkpoint. Compared to execution models supported by TM, HWBS distinguishesspeculative and non-speculative threads to avoid unnecessary value buffering and violationchecking. Non-speculative worker threads can commit their writes concurrently withoutwaiting. As a result, HWBS is regarded as a better solution for a program pattern, wheretasks in the same loop invocation are independent while tasks from different invocationsmay depend on each other.Despite its effectiveness, HWBS requires specialized hardware to detect misspeculationand recover. Programs parallelized for commodity hardware cannot benefit from it. Thislimitation motivates us to design and implement the first software-only speculative barrierfor SPECCROSS, which aims at generating scalable parallel programs for commoditymulticore machines.4.1.3 Automatic cross-invocation parallelization with software-only speculativebarrierSPECCROSS is implemented to generate multi-threaded programs running on commoditymulti-core machines. SPECCROSS consists of three components: a parallelizing compiler,a profiling library and a runtime library. The parallelizing compiler automatically detectsand parallelizes a code region with many loop invocations. The profiling library determineshow aggressively to speculate and is the key to achieving high confidence speculation. Theruntime library provides support for speculative execution, misspeculation detection, andrecovery.SPECCROSS’s runtime library implements a software-only speculative barrier, whichworks as a light-weight substitution for HWBS on commodity hardware. This runtime55
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AUTOMATICALLY EXPLOITINGCROSS-INVOC
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techniques. Among twenty programs f
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in particular. Their professionalis
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ContentsAbstract . . . . . . . . .
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4.5.4 Load Balancing Techniques . .
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2.4 Sequential Loop Example for DOA
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4.5 Overview of SPECCROSS: At compi
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1.1 Limitations of Existing Approac
Page 18 and 19: advanced forms of parallelism (MPI,
Page 20 and 21: the graph stands for an iteration i
Page 22 and 23: 1.2 ContributionsFigure 1.5 demonst
Page 24 and 25: 1.3 Dissertation OrganizationChapte
Page 26 and 27: alias the array regular via inter-p
Page 28 and 29: 1 for (i = 0; i < M; i++){2 node =
Page 30 and 31: 1 cost = 0;2 node = list->head;3 Wh
Page 32 and 33: example which cannot benefit from e
Page 34 and 35: These techniques are referred to as
Page 36 and 37: unnecessary overhead at runtime.Tab
Page 38 and 39: Chapter 3Non-Speculatively Exploiti
Page 40 and 41: for a variety of reasons. For insta
Page 42 and 43: 12x11x10xDOMOREPthread Barrier9xLoo
Page 44 and 45: Algorithm 1: Pseudo-code for schedu
Page 46 and 47: Algorithm 2: Pseudo-code for worker
Page 48 and 49: 3.3 Compiler ImplementationThe DOMO
Page 50 and 51: to T i . DOMORE’s MTCG follows th
Page 52 and 53: Outer_Preheaderbr BB1ABB1A:ind1 = P
Page 54 and 55: Algorithm 3: Pseudo-code for genera
Page 56 and 57: Scheduler Function SchedulerSync Fu
Page 58 and 59: SchedulerWorker1 Worker2Worker3Work
Page 60 and 61: 3.5 Related Work3.5.1 Cross-invocat
Page 62 and 63: ations during the inspecting proces
Page 64 and 65: for (t = 0; t < STEP; t++) {L1: for
Page 66 and 67: sequential_func() {for (t = 0; t <
Page 70 and 71: library provides efficient misspecu
Page 72 and 73: Workerthread 1TimeFigure 4.6: Timin
Page 74 and 75: 4.2 SPECCROSS Runtime System4.2.1 M
Page 76 and 77: takes up to 200MB memory space.To d
Page 78 and 79: checkpoint, the child spawns new wo
Page 80 and 81: Operation DescriptionFunctions for
Page 82 and 83: Main thread:main() {init();create_t
Page 84 and 85: implemented in the Liberty parallel
Page 86 and 87: Algorithm 5: Pseudo-code for SPECCR
Page 88 and 89: CROSS, since SPECCROSS can be appli
Page 90 and 91: techniques.Synchronization via sche
Page 92 and 93: Source Benchmark Function % of exec
Page 94 and 95: applied to the outermost loop, gene
Page 96 and 97: 5.2 SPECCROSS Performance Evaluatio
Page 98 and 99: and the number of checking requests
Page 100 and 101: 8x7xno misspec.with misspec.Geomean
Page 102 and 103: This thesisPrevious workSpeedup (x)
Page 104 and 105: Program Speedup6x5x4x3x2xLOCALWRITE
Page 106 and 107: for DOMORE and SPECCROSS. Others (e
Page 108 and 109: programs and it achieves a geomean
Page 110 and 111: Bibliography[1] R. Allen and K. Ken
Page 112 and 113: [15] R. Cytron. DOACROSS: Beyond ve
Page 114 and 115: [31] T. B. Jablin, Y. Zhang, J. A.
Page 116 and 117: [47] A. Nicolau, G. Li, A. V. Veide
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[62] L. Rauchwerger and D. Padua. T
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national conference on Parallel Arc
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