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Drivers & Software

tgn
Adept II

directx 12 multi gpu

Im just wondering if anyone knows what cards is supported for the multi GPU mode in DX12? I know you can cross nvidia and AMD cards for example, but how do you turn it on ETC? Considering its all software based, it shouldnt need a physical bridge between the cards. So for examaple, if i put my old R9 270X 4gb in with my RX 5700XT, will it work? There is LITERALLY NO INFO about this at all anywhere... And if there is, google for sure aint interested in showing them... Only useless articles and poor quality videos from 3 yrs ago... 

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Almost everything about multi-gpu is theoretical as there are literally only a few games that implement support. Tests have been done showing yes you can use cards from red and green teams. Again though how well this would work out in wide practice is anyone's guess. For instance with Crossfire or SLI  the games that support it were few overall and it never really had what anyone could call wide adoption. Less than 3% of PC gamers ever used more than one card at a time. The amount of AMD gamers would then be less than even a half percent of those gamers. Now that the developer of the games are responsible for building support into their DX12 engines it just doesn't seem to be happening. Why? Well there really isn't enough of a market to justify the extra trouble. PC gamers are already a very small percentage of who they code for and multi gpu users barely register as a statistic.  Most gamers today look for a single card solution that will meet their needs. It really is the best way to go to have stable, more trouble free experience. Of course you will have those that say 2 cards worked for them just fine, and that is true some had good experience but that is not opinion of most that went down that road.

Now if you do decide to try mult-gpu they say you should still use cards of similar performance levels as likely the will perform more to the lower common denominator but I have no idea much testing has really been done on this. You can find some video with testing of "Ashes of the Singularity" that test different cards.  I have seen absolutely zero information of testing with Navi based cards. I don't think Vega II supports it either. I know it doesn't do Crossfire.

I would love it if someday a standard comes around that doesn't require the extra work at the driver or developer level that would allow us to add our cards of unequal pairings and get better life out of these expensive purchases. Here is to hoping that happens, but don't hold your breath.

8-fingered
Adept III

The only game that supports heterogeneous DX12 mGPU is Ashes of the Singularity. All the others are homogeneous DX12 mGPU (with only two identical cards). With AMD drivers at least, you need to enable Crossfire to get them to do whatever magic they do that allows most DX12 mGPU capable games to find the linked pair of cards. You shouldn't need any bridges for DX12 mGPU (though AMD cards haven't used them in ages, at least not the gaming models).

I was under the understanding you actually had to make sure crossfire was disabled to do multi gpu. I could very easily be remembering this incorrectly though. Again darn near a moot point as basically nothing supports it either way.

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Not with AMD drivers and Shadow of the Tomb Raider, anyway. Crossfire not enabled, it will only use one GPU.

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Interesting as Multi GPU is not supposed to be driver controlled at all. 

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There is a 'linked adapter' mode that requires some work from the driver to identify the cards as a pair.

That would be interesting if that were true too as it would not explain how it has been done between a 2 cards of different GPU brands. They have already done test with Nvidia and AMD in same system with multi-gpu on Ashes of the Singularity and I am pretty sure NVIDIA or AMD is programming card recognition into their drivers for the others cards. I am by no means saying what you say is wrong just wondering if their if just way more options to how this can actually work that what I had thought. Again since no real support exist in hardly any game all this is pretty much a moot point anyway. 

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Ashes of the Singularity uses Heterogeneous explicit multi-gpu. I suspect that doesn't require any setup from the drivers (other than making the GPU visible as a DX12 capable device). Other games use Homogeneous explicit multi-gpu and need the driver to setup a linked node adapter. Here is more information from Microsoft.

So realistically and practically speaking even more reason why game developers won't ever support the multi gpu config in games. It even limits more of what base exists to use than before then. 

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Not sure I follow your reasoning...

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I'm saying that the combination of needed driver support or non-driver support dependent on what the developer uses in the game engine combined with if you want to mix and match makers of cards based on what might or might not be done, creates too many options for such a small potential user base that nobody is ever going to waste their time developing for such a small target market of users. It is dead before it started. 

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Getting developers to put in the effort has been and will continue to be the big problem. Engine support would help. Thankfully DX12 mGPU support is going into CRYENGINE 5.8. If Epic would put it into Unreal Engine, the problem would be solved overnight.

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Maybe cryengine will gain some steam. I would agree that if epic added it would help. I would sure think it would not take much to add it to Frostbite too. 

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It's in Frostbite (at least whatever version Battlefield 1 used)...but apparently it has issues. Hopefully they fix it.

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I am not aware of any Multi-GPU support in Frostbite. Battlfield 1 had unofficial crossfire support under DX 11, Dice never claimed it worked but AMD did release early drivers getting it working then messed that up with Wattman drivers. Battlfield had been AMD optimized until the most recent BFV. I wasn't able to find any mention of testing of Multi-GPU under Frostbite. If you have a link or two to share I would love to see it.

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doesn't sound promising if the only news is not much luck and that is going on 2 years old 

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