.. _profiler:

========
Profiler
========

As the complexity of the application increases, performance issues such as low FPS and frequent cache misses 
causing lag may arise. LVGL has internally set up some hooks for performance measurement to help developers 
analyze and locate performance issues.

Introduction
************

LVGL has a built-in trace system to track and record the timestamps of important events that occur during runtime, 
such as rendering events and user input events. These event timestamps serve as important metrics for performance analysis. 

The trace system has a configurable record buffer that stores the names of event functions and their timestamps. 
When the buffer is full, the trace system prints the log information through the provided user interface.

The output trace logs are formatted according to Android's `systrace <https://developer.android.com/topic/performance/tracing>`_
format and can be visualized using `Perfetto <https://ui.perfetto.dev>`_.

Usage
*****

Configure profiler
^^^^^^^^^^^^^^^^^^

To enable the profiler, set :c:macro:`LV_USE_PROFILER` in ``lv_conf.h`` and configure the following options:

1. Enable the built-in profiler functionality by setting :c:macro:`LV_USE_PROFILER_BUILTIN`.

2. Buffer configuration: Set the value of :c:macro:`LV_PROFILER_BUILTIN_BUF_SIZE` to configure the buffer size. A larger buffer can store more trace event information, reducing interference with rendering. However, it also results in higher memory consumption.

3. Timestamp configuration: LVGL uses the :cpp:func:`lv_tick_get` function with a precision of 1ms by default to obtain timestamps when events occur. Therefore, it cannot accurately measure intervals below 1ms. If your system environment can provide higher precision (e.g., 1us), you can configure the profiler as follows:

- Recommended configuration in **UNIX** environments:

    .. code:: c

        #include <time.h>

        static uint32_t my_get_tick_us_cb(void)
        {
            struct timespec ts;
            clock_gettime(CLOCK_MONOTONIC, &ts);
            return ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
        }

        void my_profiler_init(void)
        {
            lv_profiler_builtin_config_t config;
            lv_profiler_builtin_config_init(&config);
            config.tick_per_sec = 1000000; /* One second is equal to 1000000 microseconds */
            config.tick_get_cb = my_get_tick_us_cb;
            lv_profiler_builtin_init(&config);
        }

- Recommended configuration in **Arduino** environments:

    .. code:: c

        void my_profiler_init(void)
        {
            lv_profiler_builtin_config_t config;
            lv_profiler_builtin_config_init(&config);
            config.tick_per_sec = 1000000; /* One second is equal to 1000000 microseconds */
            config.tick_get_cb = micros; /* Use the microsecond time stamp provided by Arduino */
            lv_profiler_builtin_init(&config);
        }

4. Log output configuration: LVGL uses the :cpp:func:`LV_LOG` interface by default to output trace information. If you want to use another interface to output log information (e.g., file stream), you can redirect the log output using the following code:

    .. code:: c

        static void my_log_print_cb(const char * buf)
        {
            printf("%s", buf);
        }

        void my_profiler_init(void)
        {
            lv_profiler_builtin_config_t config;
            lv_profiler_builtin_config_init(&config);
            ... /* other configurations */
            config.flush_cb = my_log_print_cb;
            lv_profiler_builtin_init(&config);
        }

Run the test scenario
^^^^^^^^^^^^^^^^^^^^^

Run the UI scenario that you want to measure, such as scrolling a scrollable page up and down or entering/exiting an application.

Process the logs
^^^^^^^^^^^^^^^^

Save the output log as `my_trace.txt`, use `trace_filter.py` for filtering and preprocessing:

    .. code:: bash

        ./lvgl/scripts/trace_filter.py my_trace.txt

    or

    .. code:: bash

        python3 ./lvgl/scripts/trace_filter.py my_trace.txt

You will obtain a processed text file named `trace.systrace`, which roughly contains the following content:

    .. code:: text

        # tracer: nop
        #
        LVGL-1 [0] 2892.002993: tracing_mark_write: B|1|lv_timer_handler
        LVGL-1 [0] 2892.002993: tracing_mark_write: B|1|_lv_disp_refr_timer
        LVGL-1 [0] 2892.003459: tracing_mark_write: B|1|refr_invalid_areas
        LVGL-1 [0] 2892.003461: tracing_mark_write: B|1|lv_draw_rect
        LVGL-1 [0] 2892.003550: tracing_mark_write: E|1|lv_draw_rect
        LVGL-1 [0] 2892.003552: tracing_mark_write: B|1|lv_draw_rect
        LVGL-1 [0] 2892.003556: tracing_mark_write: E|1|lv_draw_rect
        LVGL-1 [0] 2892.003560: tracing_mark_write: B|1|lv_draw_rect
        LVGL-1 [0] 2892.003573: tracing_mark_write: E|1|lv_draw_rect
        ...

Import the processed `trace.systrace` file into `Perfetto <https://ui.perfetto.dev>`_ and wait for it to be parsed.

Performance analysis
^^^^^^^^^^^^^^^^^^^^

If the log parsing is successful, you will see the following screen:

.. image:: /misc/perfetto_ui.png

In the Perfetto UI, use the :kbd:`A` or :kbd:`D` keys to pan the timeline horizontally 
and the :kbd:`W` or :kbd:`S` keys to zoom in or out on the timeline. 
Use the mouse to move the focus and click on functions on the timeline to observe their execution time.

Add Measurement Point
*********************

Users can add their own measured functions:

.. code:: c

    void my_function(void)
    {
        LV_PROFILER_BEGIN;
        do_something();
        LV_PROFILER_END;
    }

Custom profiler implementation
******************************

If you wish to use a profiler method provided by your operating system, you can modify the following configurations in ``lv_conf.h``:

- :c:macro:`LV_PROFILER_INCLUDE`: Provides a header file for the profiler function.
- :c:macro:`LV_PROFILER_BEGIN`: Profiler start point function.
- :c:macro:`LV_PROFILER_END`: Profiler end point function.

Taking `NuttX <https://github.com/apache/nuttx>`_ RTOS as an example:

.. code:: c

    #define LV_PROFILER_INCLUDE "nuttx/sched_note.h"
    #define LV_PROFILER_BEGIN   sched_note_begin(NOTE_TAG_ALWAYS)
    #define LV_PROFILER_END     sched_note_end(NOTE_TAG_ALWAYS)

FAQ
***

Perfetto log parsing fails
^^^^^^^^^^^^^^^^^^^^^^^^^^

Please check the completeness of the logs. If the logs are incomplete, it may be due to the following reasons:

1. Serial port reception errors caused by a high baud rate. You need to reduce the baud rate.
2. Data corruption caused by other thread logs inserted during the printing of trace logs. You need to disable the log output of other threads or refer to the configuration above to use a separate log output interface.
3. Cross-thread calling of :c:macro:`LV_PROFILER_BEGIN/END`.The built-in LVGL profiler is designed for single-threaded use, so calling it from multiple threads can lead to thread safety issues. If you need to use it in a multi-threaded environment, you can use profiler interfaces provided by your operating system that ensure thread safety.

Function execution time displayed as 0s in Perfetto
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If the function execution time is lower than the precision of the timestamps, this situation can occur. You can refer to the configuration instructions above to use a higher precision timestamp.

Significant stuttering occurs during profiling
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

When the buffer used to store trace events becomes full, the profiler will output all the data in the buffer, which can cause UI blocking and stuttering during the output. You can optimize this by taking the following measures:

1. Increase the value of :c:macro:`LV_PROFILER_BUILTIN_BUF_SIZE`. A larger buffer can reduce the frequency of log printing, but it also consumes more memory.
2. Optimize the execution time of log printing functions, such as increasing the serial port baud rate or improving file writing speed.

Trace logs are not being output
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If the trace logs are not automatically printed when the buffer is not full, you can try the following methods to force the log output:

1. Reduce the value of :c:macro:`LV_PROFILER_BUILTIN_BUF_SIZE` to fill the buffer more quickly and trigger automatic printing.
2. Manually call or use a timer to call the :cpp:func:`lv_profiler_builtin_flush` function to force the log output.
