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The Path to Multi-core Tools

The Path to Multi-core Tools. Paul Petersen. Outline. Motivation Where are we now What is easy to do next What is missing. Motivation. Look at the way parallel software is written Threads & Locks This has not really changed for decades The names and details change

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The Path to Multi-core Tools

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  1. The Path to Multi-core Tools Paul Petersen

  2. Outline • Motivation • Where are we now • What is easy to do next • What is missing

  3. Motivation • Look at the way parallel software is written • Threads & Locks • This has not really changed for decades • The names and details change • Ultimately the languages leave it up to the user to get right • This means the user will sometimes get it wrong

  4. Breakpoint Debuggers State inspection tools MS Visual Studio Totalview, Gdb, Idb Profilers VTune™ Performance Analyzer Structural Function or Loop Statistical HW or SW based Runtime Analysis Intel® Thread Checker Intel® Thread Profiler Libraries OpenMP Threading Building Blocks Higher-level abstractionfor multi-core codes Understandable by analysis tools Where Are We Now

  5. Intel® Thread Checker • Observes the interaction in a concurrent application through memory references and synchronization operations • Compiler or binary instrumentation • Execution driven simulation • Detect incorrect threading api usage and asynchronous memory references

  6. Thread Checker - UI

  7. Intel® Thread Profiler • Observes the interactions in a concurrent application through the synchronization operations • Compiler or binary instrumentation • Event trace generation and analysis • Detects bottlenecks through critical path analysis • In a concurrent application not all computation is equally important

  8. Thread Profiler – Timeline View

  9. Tooltips provide object information Thread Profiler – Summary View Let’s filter and group this by object

  10. What Is Easy To Do Next • Enhance our current tools • Additional serial analysis • Detect opportunities for parallel execution • Improve efficiency • Focus capabilities • Expand platform coverage • Example - managed languages like C# or Java • Mining the data we have now • Suggest which problems should be tackled first

  11. What Is Missing • Performance Projections • What-If analysis is very hard to do accurately • You need a very details system model, and very accurate understanding of what will change by running on a different system • Changing the number of threads, can cause non-linear scaling problems by exposing a bottleneck that did not appear to be significant as smaller thread counts

  12. What Else Is Missing • Defect Detection • Moving from asynchronous memory access detection • To non-atomic object access detection. • Users typically assume that modifications to “objects” are atomic • But they have a hard time describing what is the “object” at any point in time.

  13. And Everything Else… • A tool is, among other things, a device that provides a mechanical or mental advantage in accomplishing a task • This talk has focused on a collection of analysis tools specifically designed to aid in understanding threaded applications

  14. Conclusion • Multi-core software poses many challenges that sequential software does not face • We have the first round of tools specifically designed for the problems faced by the way parallel software is written • These tools are limited to mostly just observing what happened, and reporting interesting facts about the program. • They have a hard time generalizing these observations

  15. The The The The Path Path Path Path To To To To Multi-core Multi-core Multi-core Multi-core Tools Tools Tools Tools

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