{"id":25898,"date":"2020-04-22T14:36:10","date_gmt":"2020-04-22T14:36:10","guid":{"rendered":"https:\/\/devblogs.microsoft.com\/cppblog\/?p=25898"},"modified":"2020-05-25T02:15:00","modified_gmt":"2020-05-25T02:15:00","slug":"finding-build-bottlenecks-with-cpp-build-insights","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/cppblog\/finding-build-bottlenecks-with-cpp-build-insights\/","title":{"rendered":"Finding build bottlenecks with C++ Build Insights"},"content":{"rendered":"

C++ Build Insights offers more than one way to investigate your C++ build times. In this article, we discuss two methods that you can use to identify bottlenecks in your builds: manually by using the vcperf analysis tool<\/a>, or programmatically with the C++ Build Insights SDK<\/a>. We present a case study that shows how to use these tools to speed up the Git for Windows open source project. We hope these tutorials will come in handy when analyzing your own builds.<\/p>\n

How to obtain and use vcperf<\/strong><\/span><\/p>\n

The examples in this article make use of vcperf<\/em>, a tool that allows you to capture a trace of your build and to view it in the Windows Performance Analyzer (WPA). The latest version is available in Visual Studio 2019.<\/p>\n

1. Follow these steps to obtain and configure vcperf <\/em>and WPA:<\/strong><\/span><\/p>\n

    \n
  1. Download and install the latest Visual Studio 2019<\/a>.<\/li>\n
  2. Obtain WPA by downloading and installing the latest Windows ADK<\/a>.<\/li>\n
  3. Copy the perf_msvcbuildinsights.dll<\/em> file from your Visual Studio 2019\u2019s MSVC installation directory to your newly installed WPA directory. This file is the C++ Build Insights WPA add-in, which must be available to WPA for correctly displaying the C++ Build Insights events.\n
      \n
    1. MSVC\u2019s installation directory is typically: C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\{<\/span>Edition<\/span>}<\/span>\\VC\\Tools\\MSVC\\{Version}\\bin\\Hostx64\\x64<\/code>.<\/li>\n
    2. WPA\u2019s installation directory is typically: C:\\Program Files (x86)\\Windows Kits\\10\\Windows Performance Toolkit<\/code>.<\/li>\n<\/ol>\n<\/li>\n
    3. Open the perfcore.ini<\/em> file in your WPA installation directory and add an entry for the perf_msvcbuildinsights.dll<\/em> file. This tells WPA to load the C++ Build Insights add-in on startup.<\/li>\n<\/ol>\n

      You can also obtain the latest vcperf<\/em> and WPA add-in by cloning and building the vcperf GitHub repository<\/a>. Feel free to use your built copy in conjunction with Visual Studio 2019!<\/p>\n

      2. Follow these steps to collect a trace of your build:<\/strong><\/span><\/p>\n

        \n
      1. Open an elevated x64 Native Tools Command Prompt for VS 2019<\/em><\/strong>.<\/li>\n
      2. Obtain a trace of your build:\n
          \n
        1. Run the following command: vcperf \/start MySessionName<\/code>.<\/li>\n
        2. Build your C++ project from anywhere, even from within Visual Studio (vcperf<\/em> collects events system-wide).<\/li>\n
        3. Run the following command: vcperf \/stop MySessionName outputFile.etl<\/code>. This command will stop the trace, analyze all events, and save everything in the outputFile.etl<\/em> trace file.<\/li>\n<\/ol>\n<\/li>\n
        4. Open the trace you just collected in WPA.<\/li>\n<\/ol>\n

          Using the Build Explorer view in WPA<\/strong><\/span><\/p>\n

          The first thing you\u2019ll want to do when first opening your trace in WPA is to open the Build Explorer<\/em><\/strong> view. You can do so by dragging it from the Graph Explorer<\/em><\/strong> pane to the Analysis<\/em><\/strong> window, as shown below.<\/p>\n

          \"Image<\/p>\n

          The Build Explorer view offers 4 presets that you can select from when navigating your build trace:<\/p>\n

            \n
          1. Timelines<\/li>\n
          2. Invocations<\/li>\n
          3. Invocation Properties<\/li>\n
          4. Activity Statistics<\/li>\n<\/ol>\n

            Click on the drop-down menu at the top of the view to select the one you need. This step is illustrated below.<\/p>\n

            <\/p>\n

            In the next 4 sections, we cover each of these presets in turn.<\/p>\n

            Preset #1: Timelines<\/strong><\/span><\/p>\n

            The Timelines <\/em><\/strong>preset shows how parallel invocations are laid out in time over the course of your build. Each timeline represents a virtual thread on which work happens. An invocation that does work on multiple threads will occupy multiple timelines.<\/p>\n

            N.B. <\/strong>Accurate parallelism for code generation is only available starting with Visual Studio 2019 version 16.4. In earlier versions, all code generation for a given compiler or linker invocation is placed on one timeline.<\/p>\n

            When viewing the Timelines<\/em><\/strong> preset, hover over a colored bar to see which invocation it corresponds to. The following image shows what happens when hovering over a bar on the 5th<\/sup> timeline.<\/p>\n

            <\/p>\n

            Preset #2: Invocations<\/strong><\/span><\/p>\n

            The Invocations <\/em><\/strong>preset shows each invocation on its own timeline, regardless of parallelism. It gives a more detailed look into what\u2019s happening within the invocations. With this preset, hovering over a colored bar displays the activity being worked on by an invocation at any point in time. In the example below, we can see that the green bar in Linker 58<\/em> <\/strong>corresponds to the whole program analysis activity, a phase of link time code generation. We can also see that the output for Linker 58 <\/em><\/strong>was c2.dll<\/em><\/strong>.<\/p>\n

            <\/p>\n

            Preset #3: Invocation Properties<\/strong><\/span><\/p>\n

            The Invocation Properties<\/em><\/strong> preset shows various properties for each invocation in the table at the bottom of the view. Find the invocation you are interested in to see miscellaneous facts about it such as:<\/p>\n