Problem: 3D-accelerated elements run like hot garbage on second video card, but normally on first video card.

glxgears shows 1 FPS on monitors connected to second video card, 60 FPS on monitors connected to first video card.

Both video cards are ATI AMD HD6000 series (Northern Islands) using open source radeon driver on openSUSE Leap 42.3 Linux. Monitors include different aspect ratios, including portrait and landscape orientations.

Suspected problem was related to VSYNC because vblank_mode=0 glxgears displayed expected performance on all monitors.

Solution: Followed guidance found on Fedora forum:

Create /etc/X11/xorg.conf.d/20-radeon.conf with following:

Section "Device"
Identifier "vga"
Driver "radeon"
Option "AccelMethod" "EXA"
Option "RenderAcess" "on"
Option "ColorTiling" "on"
Option "EXAVSync" "off"
Option "EXAPixmaps" "on"
Option "AccelDFS" "on"
Option "SwapbuffersWait" "false"
EndSection

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