I recently switched from AMD 6970 Crossfire to GTX 980 SLI. I’ve been having a hard time getting SLI to work at all in Linux; in all other SLI modes than “sfr” I get terrible artifacts and painting issues, where dragging a window in Ubuntu Unity desktop keeps drawing several previous positions (and tooltips) on alternating frames. The result is a really flashy screen. Curiously, when logging out the dimming overlay displayed by Unity will clear all of these artifacts.
When I use SLI in “sfr” mode, SLI seems to work, but the highest rate I can get from xrandr and nvidia-settings is 85 Hz, despite having a 144 Hz display (Asus ROG Swift PG278Q). Xrandr refuses to set the rate above 85 Hz when this mode is enabled. (I also see a horizontal black bar in the middle of screen when I log into a desktop session, opening a terminal seems to be enough to get rid of it.)
Turning SLI off, logging out and logging back in again results in a clean desktop with 144 Hz rate automatically chosen.
I initially tried to get this setup working with SLI on Ubuntu 14.10 with the latest stable drivers, then upgraded to the latest beta driver, and finally upgraded to Ubuntu 15.04 beta due to finding some mentions of a similar sounding bug being fixed in compiz between the two releases. Sadly that didn’t help.
I tried to find other posts related to this issue, but I was unable to find anything recent. https://devtalk.nvidia.com/default/topic/775250/enabling-sli-makes-all-the-windows-start-flashing-on-ubuntu-14-04/ might be the same issue based on the description in the first post.
I’m happy to answer any further questions and helping out solving the issue. I’m not (yet) intimately familiar with the graphics stack on modern Linux but I’m willing to learn and help.
nvidia-bug-report.log.gz (147 KB)