Is it a well-known problem in Beta driver 346.22? SLI mode seems to be not operational: when I switch it on using
I get black screen on X server restart(and non responsive system. so not able to switch into another vt). Without the SLI option the driver works. GNU/Linux is 32 bit Slackware 14.1/current with xorg 1.15.2(and yes the kernel option to increase vmalloc is set to 384 Mb, without it the nvidia xorg driver is failing). My hardware is 2xGTX 970 (two identical MSI Gaming 4G boards in SLI). Previous driver version (343.xx) seemed to work with SLI X config option turned on, but had some random lockups, so I upgraded to the latest beta :)
Update: later I discovered that it’s not 100% reproducible: I got black screen only on X restart first time(after driver installation without reboot - maybe some problem with old kernel module not unloaded), but the next time I booted - it was OK. BTW OpenGL performance in SLI “on” mode seems to have dropped noticeably, from ~30 to ~20 fps in Unigine Valley 1.0(QHD, ultra) benchmark. (but have to double-check this)
I confirm FPS drop from 30 to 20 in Unigine Valley on adding
Option "SLI" "on"
OR
Option "SLI" "afr"
No noticeable FPS drop if SLI is set to “sfr” or “aa”. BTW if I set “Enable SLI Visual Indicator” in nvidia-settings - I can see it in OpenGL apps. And in SFR mode the horizontal line even moves up and down in D3, stays in the middle in Unigine Valley. The latter doesn’t detect the second GPU in any SLI mode, its “GPU monitor” always displays just single GTX 970 :( Still I see no even small FPS increase anywhere.
Hate to be the bearer of bad news but SLI for Linux is worse than useless, your experience is normal. AFR is your best bet, when it works it does help, but normally SLI just causes issues.
Also another 346.35 x64 problem when sli is on: ubuntu 14.10 default desktop suffers massive flickering of windows. Had to revert to sli off to just be able to use GUI. Slackware 32 bit had no such problems with the same driver, but kde is used there.