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TotalView Debugger On Blue Gene
- 1. Scalable Debugging with TotalView on Blue Gene John DelSignore, CTO TotalView Technologies
- 2. Agenda • TotalView on Blue Gene – A little history – Current status • Recent TotalView improvements – ReplayEngine (reverse debugging) – Remote Display – TotalView Script (batch debugging) • Future work – BG/* – Heterogeneous systems – Many core, transactional memory, speculative execution – Petascale debugging TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 2
- 3. Supported Blue Gene Architectures and Compilers • Blue Gene/L and Blue Gene/P • Languages / Compilers – C/C++, Fortran, Assembly – GNU Compilers – IBM Compilers – IBM OpenMP (on BG/P) • Parallel Environments – IBM MPI – IBM OpenMP (on BG/P) – Pthreads (BG/P) • Runtime linking/loading (BG/P) – Shared libraries – Dynamically loaded shared libraries TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 3
- 4. Blue Gene Architecture • TotalView client (GUI/CLI) runs on the Front End node • Client communicates with the TotalView debugger servers running on the I/O nodes via a socket • The debugger servers communicate with the CIOD to control processes and threads running on the Compute nodes • Fanout ratios (CNs/server) – BG/L: 3264, 2 cores/CN, 128 threads/server – BG/P:128256, 4 cores/CN, 1024 threads/server – Ratio increasing (8K thr/svr?) – Parallelize server operation TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 4
- 5. TotalView Blue Gene/L Support • TotalView involvement since 2003 • Support for Blue Gene/L since 2005 • Debugging interfaces developed via close collaboration with IBM • Used on DOE/NNSA/LLNL's Blue Gene/L system containing 212 K cores – Heap memory debugging support added – Blue Gene/L scaling and performance tuning project – TotalView has debugged jobs as large as 8,192 processes (LLNL) • Work on Blue Gene/L facilitated Blue Gene/P support TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 5
- 6. TotalView Blue Gene/P Support • Blue Gene/P supported since Q4 2007 • Continued close collaboration with IBM to develop multithreaded debugging interfaces • Support for shared libraries and dynamically loaded libraries • Scalability improvements • TotalView has debugged jobs as large as 32K (Jülich) TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 6
- 7. TotalView Blue Gene/P Sites • Currently running at over 30 sites in Germany, France, UK, and US, including – Argonne – Boston University – Daresbury – IDRIS – Jülich – LLNL – Max Planck – ORNL – Princeton University – Rensselaer Polytechnic Institute • Jülich workshop, March 08 • Argonne workshop, May 08 TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 7
- 8. Recent TotalView Improvements on Blue Gene and Linux • Remote Display – Run a remote version of the TotalView GUI… – …display it locally, with fast, interactive performance – Easy, fast, secure • tvscript – Simplifies debugging batch jobs – Event/action paradigm – Configurable • ReplayEngine – Step execution back in time – Uses reverse debugging technology – Linux x86 and x8664 (currently only) TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 8
- 9. Remote Display • Presents a window on your machine that will display TotalView executing on a remote system • Two components: – Client, runs on the local system, available for Linux x86, x8664 Windows XP, Vista – Server, which runs on any system supported by TotalView, invisibly managing the connections between the host and client • The Client also provides for submission of jobs to batch queuing systems PBS Pro and LoadLeveler TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 9
- 10. Batch Scripting • Designed for debugging in a batch environment • tvscript lets you define the events to act on, the actions to take when an event occurs • Typical events – Action point (e.g., breakpoint) – Memory error (e.g., malloc returns 0, guard block corruption) – Errors (e.g., SEGV, FPE) • Typical actions – Display a backtrace – List memory leaks – Print variables and arrays • Configurable – Supports external script files – Allows generation of even more complex actions and events TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 10
- 11. Replay Engine • Intuitive user interface, integrated with TotalView Step forward over functions Step backward over functions Step forward into functions Step backward into functions Advance forward out of current Advance backward out of current Function, after the call Function, to before the call Advance forward to selected line Advance backward to selected line Advance forward to “live” session TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 11
- 12. Possible Future Blue Gene Work • BG/* support – Support future generations of Blue Gene • Fast conditional breakpoints/watchpoints – Expressions compiled/patched into target, excute in parallel, about 10usecs/expression • Asynchronous thread control – Thread barrier breakpoint, thread single stepping • User programmable visual data – Allows user define complex data access function • Debugging optimized code • Postmortem debugging • Fast DLL debugging interface • LLNL collaboration for scalable subset attach – Integrates with lightweight tools such as STAT TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com 12
- 13. Possible Other Future Work • Scalability/performance – Continue scalability and performance improvements – Treebased infrastructure for logarithmic scaling – Petascale debugging – Hundreds of thousands of threads • Heterogeneous systems – IBM Roadrunner (x8664/Cell) – GPUs • Emerging technologies – Many core – Transactional memory – Speculative execution TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com <number>
- 14. Questions? More Information • Blue Gene Technical Development Interest Group Contact chris.gottbrath@totalviewtech.com – • Technical support support@totalviewtech.com – • BG LLNL case study www.totalviewtech.com/pdf/case_study_scientific_computing.pdf – • Customer training or webinars contacttraininggroup@totalviewtech.com – • Web site – www.totalviewtech.com TotalView Technologies – Confidential and Proprietary – Plans Subject to Change without Notice www.totalviewtech.com <number>