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Aroon Nataraj, Matthew Sottile, Alan Morris, Allen D. Malony, Sameer Shende { anataraj, matt, amorris, malony, shende}@cs.uoregon.edu http://www.cs.uoregon.edu/research/tau Department of Computer and Information Science Performance Research Laboratory University of Oregon TAUoverSupermon (ToS) Low-Overhead Online Parallel Performance Monitoring
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France2 Acknowledgements LANL - Ron? ANL - cluster access? LLNL - cluster access? Funding Ack?
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France3 Outline Problem, Motivations & Requirements Our Approach - Coupling TAU and Supermon What is TAU? What is Supermon? And how we coupled them? The Rationale Experimentation Online monitored data visualized Performance / Scalability results investigated Work in progress and Future plans Related Work Conclusion
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France4 TAU Transport Substrate - Motivations Transport Substrate Enables movement of measurement-related data TAU, in the past, has relied on shared file-system Some Modes of Performance Observation Offline / Post-mortem observation and analysis least requirements for a specialized transport Online observation long running applications, especially at scale dumping to file-system can be suboptimal Online observation with feedback into application in addition, requires that the transport is bi-directional Performance observation problems and requirements are a function of the mode
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France5 TAU Performance System Tuning and Analysis Utilities (14+ year project effort) Performance system framework for HPC systems Integrated, scalable, flexible, and parallel Multiple parallel programming paradigms Parallel performance mapping methodology Portable (open source) parallel performance system Instrumentation, measurement, analysis, and visualization Portable performance profiling and tracing facility Performance data management and data mining Scalable (very large) parallel performance analysis Partners Research Center Jülich, LLNL, ANL, LANL, UTK
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France6 TAU Performance Observation Methodology Advocate event-based, direct performance observation Observe execution events Types: control flow, state-based, user-defined Modes: atomic, interval (enter/exit) Instrument program code directly (defines events) Modify program code at points of event occurrence Different code forms (source, library, object, binary, VM) Measurement code inserted (instantiates events) Make events visible Measures performance related to event occurrence Contrast with event-based sampling
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France7 TAU Performance System Architecture
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France8 TAU Performance System Architecture
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France9 User-level abstractions problem domain source code object codelibraries instrumentation executable runtime image compiler linkerOS VM instrumentation performance data run preprocessor Multi-Level Instrumentation and Mapping Multiple interfaces Information sharing Between interfaces Event selection Within levels Between levels Mapping Performance data is associated with high- level semantic abstractions
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France10 TAU Instrumentation Approach Support for standard program events Routines, classes and templates Statement-level blocks and loops Support for user-defined events Begin/End events (“user-defined timers”) Atomic events (e.g., size of memory allocated/freed) Selection of event statistics Support definition of “semantic” entities for mapping Support for event groups (aggregation, selection) Instrumentation selection and optimization Instrumentation enabling/disabling and runtime throttling
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France11 TAU Instrumentation Mechanisms Source code Manual (TAU API, TAU component API) Automatic (robust) C, C++, F77/90/95 (Program Database Toolkit (PDT)) OpenMP (directive rewriting (Opari), POMP2 spec) Object code Pre-instrumented libraries (e.g., MPI using PMPI) Statically-linked and dynamically-linked Executable code Dynamic instrumentation (pre-execution) (DyninstAPI) Virtual machine instrumentation (e.g., Java using JVMPI) TAU_COMPILER to automate instrumentation process
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France12 TAU Measurement Approach Portable and scalable parallel profiling solution Multiple profiling types and options Event selection and control (enabling/disabling, throttling) Online profile access and sampling Online performance profile overhead compensation Portable and scalable parallel tracing solution Trace translation to EPILOG, VTF3, and OTF Trace streams (OTF) and hierarchical trace merging Robust timing and hardware performance support Multiple counters (hardware, user-defined, system) Measurement specification separate from instrumentation
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France13 TAU Measurement Mechanisms Parallel profiling Function-level, block-level, statement-level Supports user-defined events and mapping events TAU parallel profile stored (dumped) during execution Support for flat, callgraph/callpath, phase profiling Support for memory profiling (headroom, leaks) Tracing All profile-level events Inter-process communication events Inclusion of multiple counter data in traced events Compile-time and runtime measurement selection
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France14 TAU-over-MRNET (ToM) Project MRNET as a Transport Substrate in TAU (Reporting early work done in the last week.)
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France15 Requirements Improve performance of transport NFS can be slow and variable Specialization and remoting of FS-operations to front-end Data Reduction At scale, cost of moving data too high Sample in different domain (node-wise, event-wise) Control Selection of events, measurement technique, target nodes What data to output, how often and in what form? Feedback into the measurement system, feedback into application Online, distributed processing of generated performance data Use compute resource of transport nodes Global performance analyses within the topology Distribute statistical analyses easy (mean, variance, histogram), challenging (clustering)
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France16 Approach and First Prototype Measurement and measured data transport are separate No such distinction in TAU Created abstraction to separate and hide transport TauOutput Did not create a custom transport for TAU Use existing monitoring/transport capabilities Supermon (Sottile and Minnich, LANL) Piggy-backed TAU performance data on Supermon channels Correlate system-level metrics from Supermon with TAU application performance data
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France17 Rationale Moved away from NFS Separation of concerns Scalability, portability, robustness Addressed independent of TAU Re-use existing technologies where appropriate Multiple bindings Use different solutions best suited to particular platform Implementation speed Easy, fast to create adapter that binds to existing transport MRNET support was added in about a week Says a lot about usability of MRNET
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France18 ToM Architecture TAU Components* Front-End (FE) Filters Back-End (BE) * Over MRNet API No-Backend-Instantiation mode Push-Pull model of data retrieval No daemon Instrumented application contains TAU and Back-End Two channels (streams) Data (BE to FE) Control (FE to BE)
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France19 ToM Architecture Applicaton calls into TAU Per-Iteration explicit call to output routine Periodic calls using alarm TauOutput object invoked Configuration specific: compile or runtime One per thread TauOutput mimics subset of FS-style operations Avoids changes to TAU code If required rest of TAU can be made aware of output type Non-blocking recv for control Back-end pushes Sink pulls
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France20 Simple Example (NPB LU - A, Per-5 iterations) Exclusive time
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France21 Simple Example (NPB LU - A, Per-5 iterations) Number of calls
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France22 Comparing ToM with NFS TAUoverNFS versus TAUoverMRNET 250 ssor iterations 251 TAU_DB_DUMP operations Significant advantages with specialized transport substrate Similar when using Supermon as the substrate Remoting of expensive FS meta-data operations to Front-End NPB LU (A) 32 Processors Over NFS (secs) Over MRNET (secs) % Improvement over NFS Total Runtime45.5136.5019.79 TAU_DB_DUMP8.580.36695.73
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France23 Playing with Filters Downstream (FE to BE) multicast path Even without filters, is very useful for control Data Reduction Filters are integral to Upstream path (BE to FE) W/O filters loss-less data reproduced D-1 times Unnecessary large cost to network Filter 1: Random Sampling Filter Very simplistic data reduction by node-wise sampling Accepts or Rejects packets probabilistically TAU Front-End can control probability P(accept) P(accept)=K/N (N = # leafs, K is user constant) Bounds number of packets per-round to K
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France24 Filter 1 in Action (Ring application) Compare different P(accept) values 1, 1/4, 1/16 Front-End unable to keep up Queuing delay propagated back
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France25 Other Filters Statistics filter Reduce raw performance data to smaller set of statistics Distribute these statistical analyses from Front-End to the filters Simple measures - mean, std.dev, histograms More sophisticated measures - distributed clustering Controlling filters No direct way to control Upstream-filters not on control path Recommended solution place upstream filters that work in concert with downstream filters to share control information requires synchronization of state between upstream and downstream filters Our Echo hack Back-Ends transparently echo Filter-Control packets back upstream this is then interpreted by the filters easier to implement control response time may be greater
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France26 Feedback / Suggestions Easy to integrate with MRNET Good examples documentation, readable source code Setup phase Make MRNET intermediate nodes listen on pre-specified port Allow arbitrary mrnet-ranks to connect and then set the Ids in the topology Relaxing strict apriori-ranks can make setup easier Setup in Job-Q environments difficult Packetization API can be more flexible Current API is usable and simple (var-arg printf style) Composing a packet over a series of staggered stages difficult Allow control over how buffering is performed Important in a push-pull model as data injection points (rates) independent of data retrieval Is not a problem in a purely pull model
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France27 TAUoverMRNET - Contrast TAUoverSupermon Supermon (cluster-monitor) vs. MRNet (reduction-network) Both light-weight transport substrates Data format Supermon: ascii s-expressions MRNET: packets with packed (binary?) data Supermon Setup Loose topology No support/help in setting up intermediate nodes Assume Supermon is part of the environment MRNET Setup Strict topology Better support for starting intermediate nodes With/Without Back-End instantiation (TAU uses latter) Multiple Front-Ends (or sinks) possible with Supermon MRNET, front-end needs to program this functionality No exisiting pluggable “filter” support in Supermon Performing aggregation is more difficult with Supermon. Supermons allows buffer-policy specification, MRNET does not
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TAUoverSupermon (ToS)EuroPar 2007, Rennes, France28 Future Work Dyninst Tighter integration of source and binary instrumentation Conveying of source information to binary level Enabling use of TAU’s advanced measurement features Leveraging TAU’s performance mapping support Want robust and portable binary rewriting tool MRNet Development of more performance filters Evaluation of MRNet performance for different scenarios Testing at large scale Use in applications
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