Question / Help Streaming with NVLink

[JoKo87100]

Hi,

this is not an actual issue, but a consideration.
With Nvidia turing we got NVLink, which is the successor of SLI. That meens, that we now have 50 times more bandwith and so it's possible to share the VRAM between the two cards. Unlike ealier you now double the VRAM, when you add a second card into your system.
With SLI we always got problems with capturing in obs, because a Gamecapture Source always grabs the Frames directly off the VRAM of ONE Card, right? So if we run an sli system, we can just get half of the frames in obs, because it has no access to the second cards frames. Correct me, if i'm wrong.
With turing both cards share there VRAM, so it should theoretically be possible to capture all frames from an NVLink System, right? That could mean, that we now finally have no need for a secondary streaming pc, because we can easily avoid the graficcards performance limit and have enough ressources for both streaming and gaming on one system. So all the downsides of a two pc setup would no longer be a problem.
Does anyone of you have any experience with that NVLink thing with obs?

Regards
Johannes

 

[Suslik V]

How capture works, described in this post (starting from the "...There are two "game capture" techniques through hooks..."): https://obsproject.com/forum/threads/any-changes-with-an-upgraded-video-card.40855/#post-184243

OBS always got pictures that it can get. Otherwise, you'll get black screen instead of captured frames (not half of the frames, not frames from first card etc.).

Better to have single video card solution if you doing capture.

 

[JoKo87100]

First thanks for your reply.
I know that obs has the least amount of issues with just a single gpu. But thats the Question! Is there no need to use the first capture methode, explained in the linked article, because nvidia turing shares the vram? As mentioned befor thats not an actual issue i've got or something, but a consideration of mine. I'm just interested :)
To your claim, that i would not get half of the frames or something, but a blackscreen, reaqd this: https://obsproject.com/forum/threads/why-exactly-is-sli-an-issue-for-obs-to-capture.19475/

 

[TryHD]

With Nvidia turing we got NVLink, which is the successor of SLI. That meens, that we now have 50 times more bandwith and so it's possible to share the VRAM between the two cards. Unlike ealier you now double the VRAM, when you add a second card into your system.
Correct me, if i'm wrong.

This is not true for games, it needs to be explicit implemented and no game does that.

 

[JoKo87100]

This is not true for games, it needs to be explicit implemented and no game does that.

are you sure? I thought this is a feature Nvidia implemented with the new architecture... Im not sure if thats software related. Theoretically the Graficscard should be able to share the memorie without any software implementation, right? But maybe you're right. Not every game supports sli... mhm

 

[Suslik V]

https://obsproject.com/forum/threads/why-exactly-is-sli-an-issue-for-obs-to-capture.19475/

@JoKo87100 I will blame @Jim for this description of how SLI works. The second card never connected to the display device, so there is no other route than display pictures on your monitor using the video card connected to it physically.

The "...OBS can only "see" captured frames of the one it is running on..." probably was an attempt to say that currently obs can't copy to the texture the picture before it displayed (as it do for the card where obs building its own composition). This is the hooks are needed for - to get the picture. All other methods are slow - SLI wouldn't help you here and it makes the things even worse.

Some brief info about the SLI (old but easy to read...)
http://developer.download.nvidia.com/whitepapers/2011/SLI_Best_Practices_2011_Feb.pdf

If NVLink is such a transparent thing for the system and for the application, then what are you waiting for? It shouldn't affect OBS functionality at all in this case.

If you need many GPUs in one PC - buy capture card and install it to the second PC.

 

[JoKo87100]

@Suslik V i didn't geht what you mean by "obs can't copy to the texture the picture before it displayed"... would you explain again what you mean?

"so there is no other route than display pictures on your monitor using the video card connected to it physically." Because of this you think there is no way to capture frames with the normal, efficient way of capturing in obs when sli or nvlink is enabled?

So conclusion: no, nvlink is Not the Solution for our Graphics limit in gaming/streaming setup in one System?.... what a shame

 

[Suslik V]

Do as you wish, there is no any conclusion. The @Jim 's post is dated 2014, docs referenced by me are 2011, you are talking about 2018...