GTX 1080 SLI does not benefit in Witcher 3

[phoenixfieryn]

Computer Type: Desktop

GPU: 2x GTX 1080 8GB no OC (factory OCed by ASUS)

CPU: Ryzen 7 1800X 4.0Ghz

Motherboard: ASUS Crosshair VI Hero latest BIOS (3008)

RAM: TridentZ RGB 32GB 3000Mhz (running 2800Mhz)

Disk: Samsung Evo 850 1TB, 2x Samsung 850 500GB (RAID 0), 3x 2TB Seagate HDD (RAID 0). Game is on the hard drive RAID.

PSU: EVGA 850 P2 Platinum 70.8A on 12V rail

OS: Windows 10 Pro 64-bit clean install (1709 16299.125)

GPU Drivers: 388.71 clean install

Description of problem: No noticeable gains from SLI in Witcher 3 1440p. Everything set to max (no hairworks) and FPS stays around 80 with either 1 or 2 cards. Focus monitor set properly. Monitor supports GSync and 165Hz. Vsync is off. Both cards are being utilized in Task Manager (95% 1st, 85% 2nd) when in SLI. 100% utilization in 1st GPU when not in SLI but FPS is the same. 3 monitors connected to the first GPU.

Troubleshooting: Set focus monitor on center monitor and I play using the center monitor. Clean installed the drivers. Used custom SLI profiles (0x280020F5, 0x280020F1, 0x280021F1). Set maximum performance and tried both SLI options in NVControl Panel (Force alternative frame 1 and 2).



Thanks

 

[n0ns3ns3]

try to go to game settings and set the resolution to 1080p.
If FPS does not change significantly, you are CPU limited - means it's not related to the cards

 

[velocityg4]

A Ryzen 1800x at 4Ghz should be capable of about 120FPS in Witcher 3 assuming no GPU bottleneck. 2800mhz RAM might knock off 5 or 6 FPS, 10 on a really bad day.

http://www.eurogamer.net/articles/digitalfoundry-2017-amd-ryzen-7-1800x-review

A single GTX 1080 should be able to put out 80 to 90 FPS at 2560x1440. SLI 130 FPS to 140 FPS. Given the limitations of your CPU. I would expect you to hit the 110 FPS to 120 FPS in SLI.
https://www.techspot.com/review/1195-palit-geforce-gtx-1080-sli/

Have you tried running onscreen overlay with MSI afterburner? So, you can see CPU usage per core, GPU usage and RAM usage simultaneously. Perhaps take a screen shot.
https://www.msi.com/blog/setting-up-osd-with-msi-afterburner

Do you have the latest BIOS installed? How about the optimized Ryzen drivers for Windows and the Ryzen power profile setup?

 

[phoenixfieryn]

Thank you both for your help. I ended up finding a solution for me and some beneficial settings that I tweaked. I ended up getting 2933Mhz RAM stable, so that helped a bit, though only 1-2 FPS. Another thing that helped me was disabling SMT, and set the CPU affinity to cores 1-7 instead of cores 0-7. That got me around 10 FPS. Finally, rolling back drivers did the trick for SLI. Witcher 3 isn't the first game to have SLI problems recently, Battlefield 1 had similar issues too. I rolled back to 378.78 3/09/2017 and miraculously, SLI worked there. I now get around 90-120FPS at 1440p ultra. I thought it was weird but so I updated back to the most recent driver and the performance decreased again, it seems like Nvidia is artificially limiting SLI performance or just broke it accidentally even though GPU utilization are around the same for both.