Merge pull request #4951 from Calinou/add-cpp-profilers-page-3.3

Add a page on using C++ profilers (3.3)

development/cpp/index.rst

@@ -1,19 +1,55 @@
 Engine development
 ==================
 
+Setting up a development environment
+------------------------------------
+
+To modify Godot's source code, you need to set up a development environment. Start here.
+
 .. toctree::
    :maxdepth: 1
-   :name: toc-devel-cpp
+   :name: toc-devel-cpp-dev-env
 
-   introduction_to_godot_development
    configuring_an_ide/index
+
+Getting started with Godot's source code
+----------------------------------------
+
+This section covers the basics that you will encounter in (almost) every source file.
+
+.. toctree::
+   :maxdepth: 1
+   :name: toc-devel-cpp-source-beginner
+
+   introduction_to_godot_development
    common_engine_methods_and_macros
    core_types
    variant_class
    object_class
    inheritance_class_tree
+
+Extending Godot by modifying its source code
+---------------------------------------------
+
+This section covers what you can do by modifying Godot's C++ source code.
+
+.. toctree::
+   :maxdepth: 1
+   :name: toc-devel-cpp-source-advanced
+
    custom_modules_in_cpp
    binding_to_external_libraries
+   custom_godot_servers
    custom_resource_format_loaders
    custom_audiostreams
-   custom_godot_servers
+
+Debugging and profiling
+-----------------------
+
+This section is about finding spots to optimize in the engine code when you need it in your project.
+
+.. toctree::
+   :maxdepth: 1
+   :name: toc-devel-cpp-debug-profiling
+
+   using_cpp_profilers

development/cpp/using_cpp_profilers.rst

@@ -0,0 +1,142 @@
+Using C++ profilers
+===================
+
+To optimize Godot's performance, you need to know what to optimize first.
+To this end, profilers are useful tools.
+
+.. note::
+
+    There is a built-in GDScript profiler in the editor, but using C++ profiler
+    may be useful in cases where the GDScript profiler is not accurate enough
+    or is missing information due to bugs in the profiler.
+
+Recommended profilers
+---------------------
+
+- `VerySleepy <http://www.codersnotes.com/sleepy/>`__ (Windows only)
+- `HotSpot <https://github.com/KDAB/hotspot>`__ (Linux only)
+
+These profilers may not be the most powerful or flexible options, but their
+standalone operation and limited feature set tends to make them easier to use.
+
+.. note::
+
+    In its latest stable release (0.90 as of writing), VerySleepy will freeze
+    when loading debug symbols. To solve this, exit VerySleepy then save
+    `this dbghelpms.dll file <https://github.com/AlanIWBFT/verysleepy/raw/0523fde86f24139fd4a041319f8b59ace12f602b/dbghelp_x64/dbghelpms.dll>`__
+    at the root of the VerySleepy installation folder.
+    This folder is generally located at ``C:\Program Files\Very Sleepy CS``.
+
+    If you are debugging a 32-bit application instead of 64-bit, save
+    `this dbghelpms.dll file <https://github.com/AlanIWBFT/verysleepy/raw/0523fde86f24139fd4a041319f8b59ace12f602b/dbghelp_x86/dbghelpms.dll>`__
+    in the ``32`` folder of the VerySleepy installation folder.
+
+Setting up Godot
+----------------
+
+To get useful profiling information, it is **absolutely required** to use a Godot
+build that includes debugging symbols. Official binaries do not include debugging
+symbols, since these would make the download size significantly larger.
+
+To get profiling data that best matches the production environment, you should
+compile binaries with the following SCons options:
+
+- For editor binaries: ``target=release_debug use_lto=yes``
+- For debug export templates: ``target=release_debug use_lto=yes``
+- For release export templates: ``tools=no target=release debug_symbols=yes``
+  - ``debug_symbols=yes`` is required as export templates are stripped from debugging symbols by default.
+
+It is possible to run a profiler on less optimized builds (e.g. ``target=debug`` without LTO),
+but results will naturally be less representative of real world conditions.
+
+.. warning::
+
+    Do *not* strip debugging symbols on the binaries using the ``strip`` command
+    after compiling the binaries. Otherwise, you will no longer get useful
+    profiling information when running a profiler.
+
+Benchmarking startup/shutdown times
+-----------------------------------
+
+If you're looking into optimizing Godot's startup/shutdown performance,
+you can tell the profiler to use the ``--quit`` command line option on the Godot binary.
+This will exit Godot just after it finished starting.
+The ``--quit`` option works with ``--editor``, ``--project-manager`` or
+``--path <path to project directory>`` (which runs a project directly).
+
+.. seealso::
+
+    See :ref:`doc_command_line_tutorial` for more command line arguments
+    supported by Godot.
+
+Profiler-specific instructions
+------------------------------
+
+VerySleepy
+^^^^^^^^^^
+
+- Start the Godot editor or your project first.
+  If you start the project manager, make sure to edit or run a project first.
+  Otherwise, the profiler will not track the child process since the project manager
+  will spawn a child process for every project edited or run.
+- Open VerySleepy and select the Godot executable in the list of processes on the left:
+
+.. image:: img/cpp_profiler_verysleepy_select_process.png
+
+- Click the **Profile All** button on the right to start profiling.
+- Perform the actions you wish to profile in the editor or project. When you're done, click **Stop** (*not* Abort).
+- Wait for the results window to appear.
+- Once the results window appears, filter the view to remove external modules (such as the graphics driver).
+  You can filter by module by finding a line whose **Module** matches the Godot
+  executable name, right-clicking that line then choosing
+  **Filter Module to <Godot executable name>** in the dropdown that appears.
+- Your results window should now look something like this:
+
+.. image:: img/cpp_profiler_verysleepy_results_filtered.png
+
+HotSpot
+^^^^^^^
+
+- Open HotSpot. Click **Record Data**:
+
+.. image:: img/cpp_profiler_hotspot_welcome.png
+
+- In the next window, specify the path to the Godot binary that includes debug symbols.
+- Specify command line arguments to run a specific project, with or without the editor.
+- The path to the working directory can be anything if an absolute path is used
+  for the ``--path`` command line argument. Otherwise, it must be set to that
+  the relative path to the project is valid.
+- Make sure **Elevate Privileges** is checked if you have administrative privileges.
+  While not essential for profiling Godot, this will ensure all events can be captured.
+  Otherwise, some events may be missing in the capture.
+  Your settings should now look something like this:
+
+.. image:: img/cpp_profiler_hotspot_record.png
+
+- Click **Start Recording** and perform the actions you wish to profile in the editor/project.
+- Quit the editor/project normally or use the **Stop Profiling** button in HotSpot
+  to stop profiling early. Stopping profiling early can result in cleaner profiles
+  if you're not interested in the engine's quit procedure.
+- Click **View Results** and wait for the profiling visualization to be generated:
+
+.. image:: img/cpp_profiler_hotspot_view_results.png
+
+- Use the tabs at the top to navigate between the different views. These views
+  show the same data, but in different ways. The **Flame Graph** tab is a good
+  way to see which functions take up the most time at a glance. These functions
+  are therefore the most important ones to optimize, since optimizing them will
+  improve performance the most.
+- At the bottom of all tabs except **Summary**, you will also see a list of CPU threads
+  started by the engine among with the CPU utilization for each thread.
+  This lets you see threads that can be a bottleneck at a given point in time.
+
+.. image:: img/cpp_profiler_hotspot_flame_graph.png
+
+.. note::
+
+    If you don't want the startup procedure to be included in the profile, you
+    can also attach HotSpot to a running process by clicking **Record Data**
+    then setting the **Launch Application** dropdown option to **Attach To
+    Process(es)**.
+
+    This process attachment-based workflow is similar to the one used by VerySleepy.