I've got an issue where adding a GPU to my machine and running a second screen off it causes a lot poor performance for things like gifs, or simple menu animations, or moving windows around while on Ubuntu and Mint. Also some times the mouse cursor will just lag with nothing going on.
I run one 4k screen off an R9 390, and a VGA screen off an HD 5770 (I can't just plug them both in to one card for various reasons). Everything works great when I have just the R9 running the 4k screen. When I plug the 5770 in, I get all this visual lag, especially when moving the cursor between screens.
It feels as though X is making the weaker card do all the work, or something like that.
Things I've tried:
Different drivers. I've tried all the combinations that Mint and Ubuntu offered me.
Different card - replaced the 5770 with a nVidia Geforce 210. Things got worse.
Drastically reduced the resolutions. Things got better, but the resolutions are unacceptably low.
Disabling the second screen in display settings. Things get the same as if I physically remove the second card. Ie no more lag, but no more screen.
Booting in to Windows. Everything works great, and has worked great in Windows for months now.
Any ideas?
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