.. _doc_profiler_perfetto:

Perfetto
========

.. seealso:: Please see the :ref:`tracing profiler instructions <doc_tracing_profilers>` for more information.

`Perfetto <https://perfetto.dev>`__ 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=perfetto profiler_path=path/to/perfetto`` arguments 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=perfetto 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>`_.