`gnome-shell` launched both on iGPU and dGPU

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1

I am using Lenovo Legion with hybrid graphics (AMD GPU and 3060ti 6GB GPU). When I use only the built-in screen (Full HD 144Hz) of the laptop in hybrid mode, then everything is fine. When I connect an external screen (2K 144Hz), problems start. The smoothness of animations decreases, for example, when switching between desktops. If I turn on the BIOS mode of only a discrete graphics card, then the problem with smoothness disappears, then there are problems with blinking some applications (mostly applications written in Electron). I don’t think it’s an iGPU power issue, since it’s not loaded even close.
All this time, I thought that in hybrid mode, the iGPU works as the main one, and the dGPU runs on demand.
However, when I started nvtop, I saw that all but one process was running on iGPU. For some reason, 2 gnome-shell processes were running. One worked on iGPU, the other on dGPU.

with external monitor
with external monitor1620×1108 77.2 KB

only internal monitor
only internal monitor1920×1080 94.5 KB

You can clearly see when I turned off the monitor from the laptop, the load on the dGPU immediately dropped. The memory occupied by the process in VRAM also drops to 0~. After connecting the monitor back, the situation returns to 1 image. I don’t understand why 2 gnome-shell processes are running and they are on different GPUs. I also do not know what caused the strange drop in performance when connecting a second monitor, although the iGPU is not loaded by 5-10%. But why is dGPU loaded by 10%, although it should not be busy with anything at all. Thank you in advance

Edit: drop in FPS is accompanied by some kind of screen tearing

2

Have you considered that the system may not be able to support 2 monitors at 144 Hz refresh rate?

Many can support one at that rate but a second must run at reduced refresh (maybe as low as 60 Hz). Some even limit both to the lower rate when two are attached.

My laptop is one of the first type. Internal is at 144 but when I connect a second it only gets 60.

3

I’m sure it’s not a performance issue because it doesn’t repeat on Windows. Some other parts of the interface (for example, the panel on the top right) open smoothly. As I understand it, perhaps the HDMI port is connected directly to the dGPU and the second screen is rendered on it. I would be glad if it didn’t cause problems. It feels like the iGPU processes the dGPU output and only then gives it to the screen, because there seems to be a slight delay.
I didn’t pay attention to this problem before, because I just turned on dGPU-only mode and then everything is smooth (as if using iGPU+dGPU only with a built-in screen). However, using only Nvidia dGPU causes graphics glitches in some applications due to driver and compositor support. Ironically, there are no glitches in hybrid mode. Apparently, when the compositor works with iGPU, just receiving data from dGPU, it has no problems with Nvidia (I do not understand the architecture of Gnome and Wayland, but that’s all I have so far from bug reports and other sources).