As has been mentioned previously in the thread I suspect the profiler is just not displaying the all of the GPU work being done that’s stalling the frame.
I actually realized it when I tried to measure how long frames took to render:
…
The odd thing was that although it was obvious that there was only a few frames per second rendered, the timedelta still was around 50ms which does not make sense.
Rendering on the GPU does not happen synchronously so measuring how long renderer.render will just give you the amount of time it takes to issue the draw calls not the amount of time the GPU is taking to render. If you have a lot complex geometry it’s very possible that issuing the draw calls could take 50ms while the GPU takes 250ms to finish drawing.
I never got around to creating a minimum repro case to submit to Chromium but it would probably be worth doing.