Long GUI Thread Sync causes stuttering

Stephan13

Hi there,
I'm drawing a horizontal line at 25 Hz triggered from QTimer in a ChartView. If no other animations appear on screen it is drawn fluently and without any stuttering:

Once there is another item drawn besides that line (here a digital clock as text updated every second) the duration for GUI thread sync increases significantly:

If there a more items / plots updated in parallel the situation gets even worse and the line is visibly stuttering.

How can I overcome this issue and shorten the GUI blockage / synchronization time within the render thread?
Note the 19 ms spent in renderloop (thereof 18 for render):

<7>Frame prepared with 'threaded' renderloop, polish=0, lock=0, blockedForSync=0, animations=0 - (on Gui thread) QQuickApplicationWindow_QML_55(0x226e3a8 active exposed, visibility=QWindow::Windowed, flags=QFlags<Qt::WindowType>(Window|FramelessWindowHint), name="mainWindow", geometry=0,0 1024x600)
<7>Frame rendered with 'threaded' renderloop in 6ms, sync=0, render=5, swap=1 - (on render thread)

<7>Frame prepared with 'threaded' renderloop, polish=0, lock=0, blockedForSync=0, animations=0 - (on Gui thread) QQuickApplicationWindow_QML_55(0x226e3a8 active exposed, visibility=QWindow::Windowed, flags=QFlags<Qt::WindowType>(Window|FramelessWindowHint), name="mainWindow", geometry=0,0 1024x600)
<7>Frame rendered with 'threaded' renderloop in 7ms, sync=0, render=6, swap=1 - (on render thread)

<7>Frame prepared with 'threaded' renderloop, polish=0, lock=0, blockedForSync=0, animations=0 - (on Gui thread) QQuickApplicationWindow_QML_55(0x226e3a8 active exposed, visibility=QWindow::Windowed, flags=QFlags<Qt::WindowType>(Window|FramelessWindowHint), name="mainWindow", geometry=0,0 1024x600)
<7>Frame rendered with 'threaded' renderloop in 19ms, sync=0, render=18, swap=1 - (on render thread)

<7>Frame prepared with 'threaded' renderloop, polish=0, lock=0, blockedForSync=4, animations=0 - (on Gui thread) QQuickApplicationWindow_QML_55(0x226e3a8 active exposed, visibility=QWindow::Windowed, flags=QFlags<Qt::WindowType>(Window|FramelessWindowHint), name="mainWindow", geometry=0,0 1024x600)
<7>Frame rendered with 'threaded' renderloop in 8ms, sync=0, render=6, swap=2 - (on render thread)

<7>Frame prepared with 'threaded' renderloop, polish=0, lock=0, blockedForSync=0, animations=0 - (on Gui thread) QQuickApplicationWindow_QML_55(0x226e3a8 active exposed, visibility=QWindow::Windowed, flags=QFlags<Qt::WindowType>(Window|FramelessWindowHint), name="mainWindow", geometry=0,0 1024x600)
<7>Frame rendered with 'threaded' renderloop in 6ms, sync=0, render=5, swap=1 - (on render thread)

QSG_INFO:

<7>Using sg animation driver

<7>Animation Driver: using vsync: 16.95 ms

<7>Frame rendered with 'threaded' renderloop in 0ms, sync=0, render=0, swap=0 - (on render thread)

<7>texture atlas dimensions: 1024x1024

<7>R/G/B/A Buffers:   8 8 8 0

<7>Depth Buffer:      24

<7>Stencil Buffer:    8

<7>Samples:           0

<7>GL_VENDOR:         Vivante Corporation

<7>GL_RENDERER:       Vivante GC880

<7>GL_VERSION:        OpenGL ES 3.0 V6.2.4.p2.163672

<7>GL_EXTENSIONS:     GL_EXT_blend_minmax GL_EXT_discard_framebuffer GL_EXT_frag_depth GL_EXT_multi_draw_arrays GL_EXT_multisampled_render_to_texture GL_EXT_read_format_bgra GL_EXT_robustness GL_EXT_sRGB GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_s3tc GL_EXT_texture_filter_anisotropic GL_EXT_texture_format_BGRA8888 GL_EXT_texture_rg GL_EXT_texture_sRGB_decode GL_EXT_texture_type_2_10_10_10_REV GL_OES_EGL_image GL_OES_EGL_sync GL_OES_compressed_ETC1_RGB8_texture GL_OES_compressed_paletted_te
<7>Max Texture Size: 8192

Using Qt 5.12.6 on NXP's i.MX6DL.

Thanks and best
Stephan