https://bugs.freedesktop.org/show_bug.cgi?id=108941
--- Comment #1 from Rigo Reddig rigo.reddig@gmail.com ---
I've just recently chatted to boukehaarsma23 about it, as it also affects me.
I have uploaded a video of what this looks like which you can see here:
https://www.youtube.com/watch?v=roHXWtHRhyQ
Interestingly the artifact lines appear to be aligned across the screens, vsync?
The main reason though I first came across this is by trying to manually downclock my GPU. With 2x 60Hz HDMI 1080p monitors attached the GPU is constantly in a higher power state (both mclkc and sclk) and wastes a considerable amount of power at idle. This is not a problem with 1 monitor attached.
Also of note is that even with 2 monitors attached this does not occur on Windows where the GPU idles at 300MCLK/300SCLK and is significantly cooler.
For comparison about power, according to my UPS my system idles at 112-128W when the GPU's are downclocking appropriately(1 monitor). This measurement matches with Windows where the GPU is downclocking to state 0 appropriately.
When it's not downclocking appropriately (2x monitors) it idles at anywhere between 160-176Watt.
Setup: 2x RX580 Gigabyte 8G (Monitors both on GPU0) Linux 4.19.4 (Arch Main) Latest stable KDE Plasma on X