VRWorks VR SLI

Any issues, problems or troubleshooting topics related to the additional features present in the Prepar3D Professional Plus client application.
AndreusSaicimus
Posts: 2
Joined: Mon May 11, 2020 3:32 pm

VRWorks VR SLI

Postby AndreusSaicimus » Mon May 11, 2020 4:36 pm

Good day,

From the documentation, P3d clearly already uses the single-pass stereo from NVIDIAʻs VRWorks SDK:
https://prepar3d.com/SDKv4/prepar3d/vir ... guide.html
https://developer.nvidia.com/vrworks/gr ... passstereo

But VR SLI does *not* seem to be enabled, from the tests Iʻve done. Can one of the developers confirm this as of p3dv5, version 5.0.21.34709? Additionally, is it on the roadmap? It would be an absolutely killer feature for high-end VR rigs, which are still cheaper than most dedicated hardware sims.

Before people get into the SLI debates, a few points:
(1) VR SLI is _not_ SLI. Two cards nearly always give a performance benefit for VR SLI, see here:
https://developer.nvidia.com/vrworks/graphics/vrsli
either in the form of lower latency or equal latency for higher poly-count/texture-quality/shader-features.
(2) Regretably, I can put to bed the NVLink "doubling VRAM" debates; between conversations with an NVIDIA engineer, my own understanding as an HPC dev, and my experiments on a rig with 2x 2070 Supers. I can verify that enabling SLI causes my memory usage to be mirrored on each card, i.e., the SAME data is copied to BOTH cards, which is correct for either dual-gpu alternate-frame or split-eye-stereo rendering of a single world.

AndreusSaicimus
Posts: 2
Joined: Mon May 11, 2020 3:32 pm

Re: VRWorks VR SLI

Postby AndreusSaicimus » Tue Aug 25, 2020 3:45 pm

Anyone out there? LM folks?

User avatar
Beau Hollis
Lockheed Martin
Posts: 2147
Joined: Wed Oct 06, 2010 3:25 pm

Re: VRWorks VR SLI

Postby Beau Hollis » Fri Sep 25, 2020 5:43 pm

Prepar3D v5 currently does not utilize SLI, but it's something we're looking to add in a future release. AFR isn't done by the driver in D3D12, so our existing NVAPI integration from v4 can't be used in v5. We have to write our own custom AFR implementation to get this working. The good news is that we have much more control over how multiple adapters are used in D3D12 and we already have a very robust system in place for managing resources across multiple GPUs thanks to our support for multi-adapter use cases. So when we do get it working, we expect it to scale better than it did in v4. VR is indeed a special case and wand could be handled separate from general use AFR.
Beau Hollis
Prepar3D Software Architect


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