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Comprehensive Parallel Debugging Framework: Architecture and Methodologies

This document outlines the design considerations and methodologies for a parallel debugging framework that supports applications ranging from 2 to 128K processes. It discusses the integration of multi-process and threaded models, message passing, and shared memory approaches. Key debugging strategies include breakpoints across processes, error tracing, and data snapshot examination. The framework employs a user-friendly Eclipse UI, integrating high-level debug APIs and asynchronous command/event models. Additionally, it utilizes an Architecture Independent Format (AIF) to represent data types and structures efficiently.

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Comprehensive Parallel Debugging Framework: Architecture and Methodologies

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  1. Parallel Tools PlatformParallel Debugger Greg Watson Project Leader

  2. Design Considerations • Parallel applications range from 2 to 128K processes • Combined mult-process and threaded model is possible • Some debug operations are performed on • All or a subset of processes • Individual processes • Processes are typically dependent on each other • Mixed language (e.g. C and Fortran) typical

  3. Programming Models • Message passing model • Distinct processes exchange data using messages • Explicit send/receive and collective operations • Shared memory model • Data structures are shared • Locking or atomic operations required • Currently targeting message passing, shared memory later

  4. Debugging Methodology • Breakpoint across all processes to synchronize • In master/worker, breakpoint only workers • Step all processes until error • Stepping one process typically not possible due to dependencies • Examine snapshot of data across all (or subset) of processes • Compare data from one process to another

  5. Architecture Overview • Eclipse UI front end • Reuse Debug and CDI where possible • High level parallel debug API • Process sets used for efficiency • Asynchronous command/event model • Extension point to allow alternate backends • Backend (SDM) • Startup • Command broadcast • Event aggregation • MI only used for low level debug actions

  6. UI Architecture Platform Debug UI CDT Debug UI PTP Debug UI ICDI IPCDI IPDebugger IPDebugEvent Commands Events

  7. Debug API public interface IPDebugger { publicvoid stepOver(BitList set, int count) throws PCDIException; ... } publicinterface IPDebugEvent { public BitList getSet(); ... } 101011010111111101011111 000000000111111101011111

  8. SDM Architecture ParallelDebugger Command Broadcast 0 4 8 2 1 6 3 5 9 7

  9. SDM Architecture ParallelDebugger Event Aggregation 0 4 8 2 1 6 3 5 9 7

  10. AIF • Architecture Independent Format for data • Independent of endianness, word size, character size • Fully represents data type and value • Can be used to represent complex data structures, such as linked lists • Supports all C, C++ and Fortran types • C and Java (partial) implementations • Library operations: • Conversion to/from native format • Logical and arithmetic • Formatting and display

  11. User Interface • Parallel Debug View • Global view of processes and process sets • Tooltips for fast variable access • Regiser/unregister process to display in Debug View • Parallel Breakpoint • Global - applies to all processes regardless of job or job size • Set-based - applies to a set of processes for a particular job • Color used to distinguish current set • Current line markers • Multiple markers allowed • Different markers for registered/unregistered processes • Text highlighting colors

  12. User Interface (cont…) • Variable View • Supports AIF data • Only fetches complex data types when variables are expanded • Array View • Prototype using custom widget • Allows 2-D view (slice) of multi-dimensional arrays • Likely to move to memory view

  13. Demo

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