How to verify / ascertain that Qt3D executes on GPU

[stefan-s]

I am using the off-screen renderer (3 instances of) according to Florian Blume to feed an animation to my GUI, which has 3 windows displaying each:

• a background image (video frame)
• the off-screen-rendered image of one of the above renderers
• some widgets on top.

I get the impression that the renderer code is not run on the GPU (nvidia GTX1650), because it is slow, because, if I bypass the off-screen rendering, the CPU load drops significantly.
How can I verify whether the rendering is actually executed on GPU?

[jsulm]

@stefan-s On Windows 10 you can see the utilisation of your graphics hardware in Task Manager

[stefan-s]

@jsulm I am on Ubuntu 18.04 forgot to specify that, sorry.

[stefan-s]

@stefan-s 'gpu_stat' states 26%, so that would hint towards GPU being utilized, but does not explain why the app is slow, when neither CPU nor GPU are even remotely fully loaded.