Earlier this year we learned that DirectX 12 would have a feature called Multiadapter, which can allow you to use multiple different GPUs in your system if game developers program their DX12 support to take advantage of the feature. You’ll even be able to use Nvidia and AMD cards together rather than using SLI / Crossfire, and that’s exactly what AnandTech has been testing.
Developer Oxide Games has created a special build of its real time strategy game Ashes of the Singularity which takes advantage of this new DX12 feature. It’s a resource-hungry game, and so is a great test of what the new multi-GPU setups can do. It’s just a tech demo right now, since neither the game nor the multiadapter support are finished, but the results so far are surprising (and more than a little encouraging).
AnandTech's tested the game using an Nvidia GeForce GTX Titan X and GTX 980 Ti, along with an AMD Radeon R9 Fury X and R9 Fury for the most part. AnandTech used the GTX 980 Ti and the R9 Fury X together as the main test cards, since they’re similar in price and specifications. They also used a GTX 680 and a Radeon HD 7970 together to see how the multi adapter works on older cards. As for the rest of the rig, it had a 4.2GHz Intel Core i7-4960X, along with 32GB of DDR3 RAM.
Interestingly, using the new multiadapter technology, mixed GPU setups (i.e. mixing up the manufacturers) performed better than homogenous setups. At a resolution of 2560x1440, the mixed setup of the R9 Fury X and the GTX 980 Ti came out on top (70.8 frames per second) over the combined R9 Fury X and R9 Fury (67.1 frames per second). One note is that using the Radeon card as the primary card came out with a 1.4fps (2 percent) lead over the mixed setup with the Nvidia card as the primary.
The mixed GPU setup also came out on top in overall percentage performance gains. The R9 Fury X + GTX 980 Ti setup was 75 percent faster than a single R9 Fury X, while a dual AMD setup was only 66 percent faster than a single card setup. Meanwhile, the Nvidia-led mixed setup was 64 percent faster than a single GTX 980 Ti, and the dual Nvidia setup merely saw a 46 percent performance increase.
Exciting stuff, as explicit multiadapter could allow PC gamers to take advantage of the strengths of Nvidia and AMD platforms, or get years of extra mileage out of aging graphics cards. Typically you can only run identical GPUs in tandem, but if enough developers support multiadapter through DX12, you could pair a new GTX 970 with an older GTX 660 and eke out a bit more performance.
Anandtech adds a much-needed word of caution, though: "it’s important to note that what happens from here is ultimately more in the hands of game developers than hardware developers. Given the nature of the explicit API, it’s now the game developers that have to do most of the legwork on implementing multi-GPU, and I’m left to wonder how many of them are up to the challenge. Hardware developers have an obvious interest in promoting and developing multi-GPU technology in order to sell more GPUs – which is how we got SLI and Crossfire in the first place – but software developers don’t have that same incentive."