Add documentation on how to use Tracy and Perfetto

engine_details/development/debugging/profiling/sampling_profilers.rst

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+.. _doc_sampling_profilers:
+
+Sampling profilers
+==================
+
+Recommended profilers
+---------------------
+
+- `VerySleepy <http://www.codersnotes.com/sleepy/>`__ (Windows only)
+- `HotSpot <https://github.com/KDAB/hotspot>`__ (Linux only)
+- `Xcode Instruments <https://developer.apple.com/xcode/>`__ (macOS 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.
+
+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 (but with debugging symbols),
+you should compile binaries with the ``production=yes debug_symbols=yes`` SCons options.
+
+It is possible to run a profiler on less optimized builds (e.g. ``target=template_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's done starting.
+The ``--quit`` option works with ``--editor``, ``--project-manager``, and
+``--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 so 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 from 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 shutdown 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 along 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.
+
+Xcode Instruments
+~~~~~~~~~~~~~~~~~
+
+- Open Xcode. Select **Open Developer Tool** - **Instruments** from the **Xcode** app menu:
+- Double-click on **Time Profiler** in the **Instruments** window:
+
+.. image:: img/cpp_profiler_xcode_menu.png
+
+- In the Time Profiler window, click on the **Target** menu, select **Choose target...**
+  and specify the path to the Godot binary, command line arguments, and environment variables
+  in the next window.
+
+.. image:: img/cpp_profiler_time_profiler.png
+
+- You can also attach the Time Profiler to a running process by selecting it from the **Target**
+  menu.
+
+- Click the **Start an immediate mode recording** button to start profiling.
+
+.. image:: img/cpp_profiler_time_profiler_record.png
+
+- Perform the actions you wish to profile in the editor or project. When you're done,
+  click the **Stop** button.
+
+- Wait for the results to appear.
+- At the bottom of the window you will see a call tree for all CPU threads started, and
+  the **Heaviest Stack Trace** overview.
+- Select **Hide system libraries** in the **Call Tree** menu (at the bottom of the window) to
+  remove external modules.
+- You can use the timeline at the top of the window to display details for the specific time period.
+
+.. image:: img/cpp_profiler_time_profiler_result.png

engine_details/development/debugging/profiling/tracing_profilers.rst

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+.. _doc_tracing_profilers:
+
+Tracing Profilers
+=================
+
+Godot currently supports two tracing profilers:
+`Tracy <https://github.com/wolfpld/tracy>`__ and `Perfetto <https://perfetto.dev>`__.
+
+In order to use either of them, you'll need to build the engine from source.
+If you've never done this before, please read
+:ref:`these docs <doc_compiling_index>` for the platform you want to profile on.
+You'll need to perform the same steps here, but with the addition of a single
+extra argument for ``scons``.
+
+.. _doc_tracy_profiler:
+
+Tracy for Windows, Linux, and macOS
+-----------------------------------
+
+Tracy is an Open Source profiler that runs on a wide variety of platforms,
+including Windows, Linux, and macOS. While it is primarily a tracing profiler,
+it can also periodically sample data like a
+:ref:`sampling profiler <doc_sampling_profilers>`, giving some of the benefits
+of both approaches.
+
+Build Godot with Tracy support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+First, clone the latest version of the Tracy source code ("0.13.0" at the
+time of writing) using Git:
+
+.. code-block:: shell
+
+    git clone -b v0.13.0 --single-branch https://github.com/wolfpld/tracy.git
+
+This will create a ``tracy`` directory - you can place this anywhere.
+
+Next, build the release templates for your platform using ``scons``, but adding
+the ``profiler_path=path/to/tracy`` argument with the real path to the ``tracy``
+directory, as well as ``debug_symbols=yes`` to allow Tracy's sampling features
+to work.
+
+.. note::
+
+    You don't have to build release templates, you could also build debug
+    templates, or even the editor. However, it's generally recommended to
+    profile release templates, because that is the version your players will
+    use, and it will perform differently than other types of builds.
+
+For example, to build release templates for Windows:
+
+.. code-block:: shell
+
+    scons platform=windows target=template_release debug_symbols=yes profiler_path=path/to/tracy
+
+Get the Tracy "server"
+~~~~~~~~~~~~~~~~~~~~~~
+
+In Tracy terminology, the application you are profiling is the "client", and
+the one receiving the data is the "server".
+
+If you are on Windows, you can download a pre-built ``tracy-profiler.exe``
+from the Tracy `releases page <https://github.com/wolfpld/tracy/releases>`_.
+
+However, if you're on Linux or macOS, you'll either need to find a pre-built
+binary from a package manager (like ``brew`` or ``nix``), or build it from
+source yourself.
+
+.. note::
+
+    If you do use a pre-built binary, be sure to use the same version that
+    you used when building Godot.
+
+Build the Tracy server from source
+++++++++++++++++++++++++++++++++++
+
+The full details can be found in the
+`Tracy manual <https://github.com/wolfpld/tracy/releases/latest/download/tracy.pdf>`_,
+but here is the TL;DR:
+
+.. code-block:: shell
+
+    # On Linux, Tracy uses Wayland by default, so if you use X11 add -DLEGACY=1
+    cmake -B profiler/build -S profiler -DCMAKE_BUILD_TYPE=Release
+    cmake --build profiler/build --config Release --parallel
+
+Record a trace
+~~~~~~~~~~~~~~
+
+Launch the Tracy server - you'll see something like this:
+
+.. image:: img/cpp_profiler_tracy_start.webp
+
+If you press "Connect" now, you can profile the launch of Godot. However,
+if you want to profile something specific (for example, a part of your game
+that is exhibiting performance issues), wait before pressing the button.
+
+Now, export your game using the release templates you built above, and run it.
+As soon as the both the game are running, and you have pressed the "Connect"
+button in Tracy, you'll see data coming in:
+
+.. image:: img/cpp_profiler_tracy_recording.webp
+
+When you think you've gathered enough data, press the "Stop" button. If you
+clicked somewhere and the box with the "Stop" button disappeared, you can
+click the top-left most icon to bring it back.
+
+Examining the trace
+~~~~~~~~~~~~~~~~~~~
+
+Here are some of the basic controls:
+
+- Zoom in/out with the mouse wheel
+- Right click and drag to move forward/backward on the timeline
+- In the top bar, click the left and right arrow buttons by "Frames" to move a single frame on the timeline
+
+To learn more, see the
+`Tracy manual <https://github.com/wolfpld/tracy/releases/latest/download/tracy.pdf>`_.
+
+Perfetto for Android
+--------------------
+
+Perfetto is the default tracing system for Android. In fact, its system tracing
+service has been built into the platform since Android 9.
+
+Build Godot with Perfetto support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+First, clone the latest version of the Perfetto source code ("53.0" at the
+time of writing) using Git:
+
+.. code-block:: shell
+
+    git clone -b v53.0 --single-branch https://github.com/google/perfetto.git
+
+This will create a ``perfetto`` directory - you can place this anywhere.
+
+Next, build the Android debug or release templates for your architecture using
+``scons`` (per :ref:`Compiling for Android <doc_compiling_for_android>`), but
+adding the ``profiler_path=path/to/perfetto`` argument with the real path to
+the ``perfetto`` directory.
+
+.. note::
+
+    It's generally recommended to profile release templates, because that is
+    the version your players will use, and it will perform differently than
+    other types of builds. However, in the case of Android, it can sometimes
+    be useful to use debug templates, because Godot can only do remote
+    debugging of games exported from debug templates.
+
+For example, to build the release templates for arm64:
+
+.. code-block:: shell
+
+    scons platform=android target=template_release arch=arm64 generate_android_binaries=yes profiler_path=path/to/perfetto
+
+Configuration
+~~~~~~~~~~~~~
+
+Perfetto requires a configuration file to tell it which events to track.
+
+Create a file called ``godot.config`` inside of the ``perfetto`` directory
+with this content:
+
+.. code-block:: text
+
+    # Trace for 10 seconds.
+    duration_ms: 10000
+
+    buffers {
+        size_kb: 32768
+        fill_policy: RING_BUFFER
+    }
+
+    # Write to file once every second to prevent overflowing the buffer.
+    write_into_file: true
+    file_write_period_ms: 1000
+
+    # Track events in the "godot" category.
+    data_sources {
+        config {
+            name: "track_event"
+            track_event_config {
+                enabled_categories: "godot"
+            }
+        }
+    }
+
+Record a trace
+~~~~~~~~~~~~~~
+
+Finally, launch your game on an Android device using the export templates you
+built earlier.
+
+When you're ready to record a trace (for example, when you've hit the part of
+your game that is exhibiting performance issues), you can use this script that
+comes with the Perfetto source code:
+
+.. code-block:: shell
+
+    cd perfetto
+    ./tools/record_android_trace -c godot.config
+
+This will record for 10 seconds (per the configuration), or until you press
+:kbd:`Ctrl + C`.
+
+Examining the trace
+~~~~~~~~~~~~~~~~~~~
+
+As soon as that script exits, it will launch the Perfetto UI in a web browser.
+
+To see the Godot events, expand the row for your application by clicking on its
+Android "Unique Name" (Perfetto will also include some events from system
+services in the trace).
+
+.. image:: img/cpp_profiler_perfetto.webp
+
+Then you can use the ``WASD`` keys to navigate the graph:
+
+- Press :kbd:`A` or :kbd:`D` to navigate forward or backward along the timeline
+- Press :kbd:`W` or :kbd:`S` to zoom in or out
+
+You'll probably need to zoom a bit before you're able to see the individual
+events from Godot.
+
+To learn more, see the
+`Perfetto UI documentation <https://perfetto.dev/docs/visualization/perfetto-ui>`_.