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PROFILING.md

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A note for setting up performance profiling

Often, we are not interested in profiling the entire code but only in understanding the performance of a specific region that we target to optimize. In such a case, we need to indicate the code region to profile such that a profiling tool can avoid measuring uninterested regions of the code, and focus on collecting data from where we are interested in.

  • VTune: To mark the code region to profile, we compile the code with a header and link with the static library of the tool such that we can insert the calls to start and stop profiling, which are __itt_resume() and __itt_pause().

    On LC, load the vtune module, and then find out the location of the tool by module load vtune; module show vtune

    Use the following cmake options when building WCS: -DWCS_WITH_VTUNE:BOOL=ON -DVTUNE_DIR:PATH=...

  • HPCToolkit: To mark the code region to profile, we compile the code with the header and link with the dynamic library of the tool such that we can insert the calls to start and stop profiling, which are hpctoolkit_sampling_start() and hpctoolkit_sampling_stop(). We use the dynamic one instead of static one to avoid using the linker wrapper provided by the tool for instrumentation.

    On LC, load the hpctoolkit module, and find out the location of the tool by module load hpctoolkit; module show hpctoolkit

    Use the following cmake options when building WCS: -DWCS_WITH_HPCTOOLKIT:BOOL=ON -DHPCTOOLKIT_DIR:PATH=...

  • gprof: To compile the code for generating the measurement file that can be analyzed by gprof, use the cmake option -DWCS_GPROF:BOOL=ON. It will add -pg compiler option. We are not able to define a code region to profile using gprof. However, we can selectively disable an uninteresting region of the code as described below using the macro definition WCS_PERF_PROF

  • Misc.: See src/reaction.cpp to see an example of how the start and stop is instrumented. Also, see the generated wcs_config.hpp that includes the headers for the profiling tools.

    If any of the cmake options WCS_PERF_PROF, WCS_WITH_HPCTOOLKIT or WCS_WITH_VTUNE is used, the macro definition WCS_PERF_PROF can be used to selectively disable a region of code to avoid profiling that part of the code.

    #ifndef WCS_PERF_PROF
 lines_to_be_disabled_during_profiling ....
#endif