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Software Optimization

Software Optimization. Stefan Roiser. Compilers. Compiler candidates in addition to gcc icc Is the licensing issue sorted out with openlab ? Status: AA nightlies OK, LHCb nightlies almost OK Performance testing needed l lvm Performance should be now in the same range as gcc

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Software Optimization

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  1. Software Optimization Stefan Roiser

  2. Compilers • Compiler candidates in addition to gcc • icc • Is the licensing issue sorted out with openlab? • Status: AA nightlies OK, LHCbnightlies almost OK • Performance testing needed • llvm • Performance should be now in the same range as gcc • AA nightlies are currently broken • We need one / several “reference job/s” for performance comparisons S. Roiser - LHCb SW Programme of Work

  3. Compiler options • Currently -O3 is being tested for LHCbsw stack • Again we need a “reference job” • If we optimize, how deep should be the stack? • Only LHCb projects • “Major impact” AA packages (e.g. Boost, GSL, …) • All AA packages S. Roiser - LHCb SW Programme of Work

  4. Optimization • Vectorization, compile with SSE on • How much could we possibly gain by using it? • Is the code prepared for it? probably not… • Many more compiler flags available • What is the proper combination? • Optimize on the CPU architecture level? S. Roiser - LHCb SW Programme of Work

  5. User code vectorization • “Bottom up” approach • Find patterns in user code that can be vectorized • Provide an abstraction with use of intrinsics • Optimized on the CPU architecture (== SIMD instruction set) • MP boxes appear ~1 yr after new micro architecture • Advantage -> it’s not a “big bang” but rather an incremental improve of the code base S. Roiser - LHCb SW Programme of Work

  6. Dictionary generation • Currently we use gccxml to generate dictionary information for persistency and interactive usage. The gcc version internal to gccxml is 4.2 and will not be upgraded • Closely connected to ROOT upgrade scenario for production releases • June ‘12, cling will be enabled • Dec ’12, persistency will work, maybe with genreflex replacement? • June ‘13, genreflex replacement available, S. Roiser - LHCb SW Programme of Work

  7. Possible scenarios for reflection • Stay as we are with gccxml • We need to carry new compiler options forward • Is already problematic for gcc 4.6 (disable warnings) • Use the possibility of gcc plugins • Extract “gccxml” code to produce reflection XML • Prototype exists, could be a stop-gap solution • Do nothing, we wait for ROOT/clang • Possibility to test full chain at latest in June ‘13 S. Roiser - LHCb SW Programme of Work

  8. Profiling • Little effort so far within LHCb • What do we want to profile? • CPU, Memory, Disk I/O, Network, … • Areas? • HLT, Offline productions, User analysis • Probably can be generalized for all Gaudi projects S. Roiser - LHCb SW Programme of Work

  9. Possible Tools • Static code analyzer • E.g. Coverity, can check for special patterns • Probably very good as a first approximation • Is available for LHCb software • Profiler • Flat – valgrind • Sampling – gprof, vtunes, S. Roiser - LHCb SW Programme of Work

  10. Existing Tool • CPU profiling based on intelVtune Amplifier • Used for HLT profiling so far • Extension for Gaudi algorithms (via Gaudi Auditor) CPU / Gaudi algorithm CPU / line of code S. Roiser - LHCb SW Programme of Work

  11. Final thoughts • Most of the areas of software optimization need much more investigation • All together a lot of work is needed in this area • All ranges of efforts available • Few weeks -> medium size projects • Dedicated manpower definitely necessary S. Roiser - LHCb SW Programme of Work

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