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Algorithm 5: Pseudo-code for SPECCROSS Library Function Calls Insertion1: Input P arallelLoops: Doallable or Localwritable loops in a SPECCROSS code region2: Input CrossInvocationDeps: cross-invocation dependences3: for all Loop l ∈ P arallelLoops do4: blocks = getBasicBlocks(l)5: // get the loop preheader and header6: preheader = getLoopP reheader(l)7: header = getLoopHeader(l)8: // get the loop exit basic blocks9: loopExits = getLoopExitBlocks(l)10: // get the basic blocks containing the loop backedge11: backEdgeBlocks = getBackEdgeBlocks(l)12: // insert enter barrier13: insertP t = BeginningOfBlock(preheader);14: insertEnterBarrier(insertP t);15: // insert enter task16: insertP t = BeginningOfBlock(header);17: insertEnterT ask(insertP t);18: // insert exit task19: for all basic block block ∈ blocks do20: termInst = getT erminatorInst(block)21: inertP t = Before(termInst);22: if block ∈ loopExits then23: if isUnconditional(termInst) ‖ block ∈ backEdgeBlocks then24: insertExitT ask(insertP t);25: else26: insertInvokeExitT askW henExitT aken(insertP t);27: end if28: else if block ∈ backEdgeBlocks then29: if isUnconditional(termInst) then30: insertExitT ask(insertP t);31: else32: insertInvokeExitT askW henBackEdgeT aken(insertP t);33: end if34: end if35: end for36: end for37: // insert spec access38: for all Dependence dep ∈ CrossInvocationDeps do39: srcInst = getSrcInstruction(dep);40: dstInst = getDstinstruction(dep);41: srcAddress = getAddress(srcInst);42: dstAddress = getAddress(dstInst);43: insertP t = Before(srcInst);44: insertSpecAccess(insertP t);45: insertP t = Before(dstinst);46: insertSpecAccess(insertpt);47: end for72
4.4 SPECCROSS ProfilingSPECCROSS provides a profiling API to determine whether speculation is profitable or not.In order to detect dependences, the signature of each task is compared with signatures oftasks belonging to earlier epochs. After dependences are detected between two tasks, theprofiling function records the dependence distance between them. Dependence distance isdefined as the number of tasks between two conflicting tasks. After profiling, a minimumdependence distance is determined. If the minimum dependence distance is smaller than athreshold value, speculation will not be done. By default, the threshold value is set to beequal to the number of worker threads.If the dependence distance is large, it means the program has an access pattern suitablefor barrier speculation. To reduce the possibility of misspeculation, the minimumdependence distance is passed as an input parameter to the speculation runtime library. Atruntime, the leading thread stalls if it executes beyond this distance.4.5 Related Work4.5.1 Barrier Removal TechniquesBarrier synchronization is often inserted in parallel applications conservatively. Some barrierscan be removed using static analysis if there is no cross-thread data flow. Severalbarrier removal techniques are based on disproving cross-thread dependences [50, 72, 78].Other techniques restructure code to avoid the need for barrier synchronization. Zhao etal. [79] transform an inner DOALL loop to an outer DOALL loop in order to remove barriersbetween two consecutive parallel loop invocations. Ferrero et al. [22] aggregate smallparallel loops into large ones for the same purpose. All these barrier removal techniquesrely on static analysis to remove barriers. Compared to them, SPECCROSS is not limitedby the conservativeness of static analysis. These approaches are complementary to SPEC-73
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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
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advanced forms of parallelism (MPI,
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the graph stands for an iteration i
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1.2 ContributionsFigure 1.5 demonst
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1.3 Dissertation OrganizationChapte
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alias the array regular via inter-p
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1 for (i = 0; i < M; i++){2 node =
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1 cost = 0;2 node = list->head;3 Wh
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example which cannot benefit from e
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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 68 and 69: Workerthread 1Workerthread 2Workert
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 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
Page 118 and 119: [62] L. Rauchwerger and D. Padua. T
Page 120: national conference on Parallel Arc
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