The onslaught of new 3D APIs, including Metal, Vulkan and Direct3D 12 is busting preconceptions along with performance barriers. This time around it's Microsoft's contender, showing that you'll not only be able to run mixed GPUs in a quasi-SLI / Crossfire configuration, but they can run faster than single vendor setups.
Anandtech recently had the opportunity to try out DirectX 12's "Explicit Multi-Adapter" as it's called. Ashes of the Singularity, a real-time strategy title currently in Early Access, supports the DirectX 12 API, including EMA, and Anandtech's Ryan Smith tried out a bunch of combinations, with both high-end and older cards put through their paces.
So, it's fair to say you'd expect a twin NVIDIA or AMD config to provide the best results, with EMA being more of a "Oh well, I have the cards so why not?" option. Turns out, that's not the case:
However would you believe that the mixed GPU setups are faster than the homogenous setups? Trailing the mixed setups is the R9 Fury X + R9 Fury setup, averaging 67.1fps and trailing the slower mixed setup by 3.5%. Slower still – and unexpectedly so – is the GTX 980 Ti + GTX Titan X setup, which averages just 61.6fps, some 12% slower than the GTX 980 Ti + Fury X setup.
EMA also requires one card to be the "lead" device, with the other "following". This also had an impact on frame rate:
GTX 680 + HD 7970 setup, either the GTX 680 is a bad leader or the HD 7970 is a bad follower, and this leads to this setup spinning its proverbial wheels. Otherwise letting the HD 7970 lead and GTX 680 follow sees a bigger performance gain than we would have expected for a moderately unbalanced setup with a pair of cards that were never known for their efficient PCIe data transfers. So long as you let the HD 7970 lead, at least in this case you could absolutely get away with a mixed GPU pairing of older GPUs.
The results are fascinating, but considering the benchmarks are from a single game (and the technology makes it tricky to isolate bottlenecks) it's difficult to draw definitive conclusions. It's sufficient to say that if running both an AMD and NVIDIA card provides the highest performance with DirectX 12, it'll make the next few years in the GPU market very interesting.