OS Limitations of Vulkan Multi-GPU Support

Subject: Graphics Cards | March 21, 2017 - 07:47 PM |
Tagged: windows 10, vulkan, sli, multi-gpu, crossfire

Update (March 22nd @ 3:50pm EDT): And the Khronos Group has just responded to my follow-up questions. LDA has existed since Windows Vista, at the time for assisting with SLI and Crossfire support. Its implementation has changed in Windows 10, but that's not really relevant for Vulkan's multi-GPU support. To prove this, they showed LDA referenced in a Windows 8.1 MSDN post.

In short:

Vulkan's multi-GPU extensions can be used on Windows 7 and Windows 8.x. The exact process will vary from OS to OS, but the GPU vendor can implement these extensions if they choose, and LDA mode isn't exclusive to Windows 10.

 

Update (March 21st @ 11:55pm EDT): I came across a Microsoft Support page that discusses issues with LDA in Windows 7, so it seems like that functionality isn't limited to WDDM 2.0 and Windows 10. (Why have a support page otherwise?) Previously, I looked up an MSDN article that had it listed as a WDDM 2.0 feature, so I figured DSOGaming's assertion that it was introduced with WDDM 2.0 was correct.

As such, LDA might not require a GPU vendor's implementation at all. It'll probably be more clear when the Khronos Group responds to my earlier request, though.

That said, we're arguing over how much a GPU vendor needs to implement; either way, it will be possible to use the multi-GPU extensions in Windows 7 and Windows 8.x if the driver supports it.

Update (March 21st @ 7:30pm EDT): The Khronos Group has just released their statement. It's still a bit unclear, and I've submit another request for clarification.

Specifically, the third statement:

If an implementation on Windows does decide to use LDA mode, it is NOT tied to Windows 10. LDA mode has been available on many versions of Windows, including Windows 7 and 8.X.

... doesn't elaborate what is required for LDA mode on Windows outside of 10. (It could be Microsoft-supported, vendor-supported, or something else entirely.) I'll update again when that information is available. For now, it seems like the table, below, should actually look something like this:

  Implicit Multi-GPU
(LDA Implicit)
Explicit Multi-GPU
(LDA Explicit)
Unlinked Multi-GPU
(MDA)
Windows 7 Requires GPU Vendor
LDA Implementation?

(Or Equivalent)
Requires GPU Vendor
LDA Implementation?

(Or Equivalent)
Windows 8.1 Requires GPU Vendor
LDA Implementation?

(Or Equivalent)
Requires GPU Vendor
LDA Implementation?

(Or Equivalent)
Windows 10
macOS Apple doesn't allow the Vulkan API to ship in graphics drivers.
At all.
Linux / etc.

... but we will update, again, should this be inaccurate.

Update (March 20th @ 3:50pm EDT): The Khronos Group has just responded that the other posts are incorrect. They haven't yet confirmed whether this post (which separates "device groups" from the more general "multi-GPU in Vulkan") is correct, though, because they're preparing an official statement. We'll update when we have more info.

Original Post Below (March 19th @ 9:36pm EDT)

A couple of days ago, some sites have noticed a bullet point that claims Windows-based GPU drivers will need WDDM in “linked display adapter” mode for “Native multi-GPU support for NVIDIA SLI and AMD Crossfire platforms” on Vulkan. This note came from an official slide deck by the Khronos Group, which was published during the recent Game Developers Conference, GDC 2017. The concern is that “linked display adapter” mode is a part of WDDM 2.0, which is exclusive to Windows 10.

This is being interpreted as “Vulkan does not support multi-GPU under Windows 7 or 8.x”.

khronos-2017-vulkan-alt-logo.png

I reached out to the Khronos Group for clarification, but I’m fairly sure I know what this does (and doesn’t) mean. Rather than starting with a written out explanation in prose, I will summarize it into a table, below, outlining what is possible on each platform. I will then elaborate below that.

  Implicit Multi-GPU
(LDA Implicit)
Explicit Multi-GPU
(LDA Explicit)
Unlinked Multi-GPU
(MDA)
Windows 7    
Windows 8.1    
Windows 10
macOS Apple doesn't allow the Vulkan API to ship in graphics drivers.
At all.
Linux / etc.

So the good news is that it’s possible for a game developer to support multi-GPU (through what DirectX 12 would call MDA) on Windows 7 and Windows 8.x; the bad news is that no-one might bother with the heavy lifting. Linked display adapters allow the developer to assume that all GPUs are roughly the same performance, have the same amount of usable memory, and can be accessed through a single driver interface. On top of these assumptions, device groups also hide some annoying and tedious work inside the graphics driver, like producing a texture on one graphics card and quickly giving it to another GPU for rendering.

Basically, if the developer will go through the trouble of supporting AMD + NVIDIA or discrete GPU + integrated GPU systems, then they can support Windows 7 / 8.x in multi-GPU as well. Otherwise? Your extra GPUs will be sitting out unless you switch to DirectX 11 or OpenGL (or you use it for video encoding or something else outside the game).

On the other hand, this limitation might pressure some developers to support unlinked multi-GPU configurations. There are some interesting possibilities, including post-processing, GPGPU tasks like AI visibility and physics, and so forth, which might be ignored in titles whose developers were seduced by the simplicity of device groups. On the whole, device groups was apparently a high-priority request by game developers, and its inclusion will lead to more multi-GPU content. Developers who can justify doing it themselves, though, now have another reason to bother re-inventing a few wheels.

Or... you could just use Linux. That works, too.

Again, we are still waiting on the Khronos Group to confirm this story. See the latest update, above.

AMD Supports CrossFire On B350 and X370 Chipsets, However SLI Limited to X370

Subject: Motherboards | February 26, 2017 - 01:29 AM |
Tagged: x370, sli, ryzen, PCI-E 3.0, gaming, crossfire, b350, amd

Computerbase.de recently published an update (translated) to an article outlining the differences between AMD’s AM4 motherboard chipsets. As it stands, the X370 and B350 chipsets are set to be the most popular chipsets for desktop PCs (with X300 catering to the small form factor crowd) especially among enthusiasts. One key differentiator between the two chipsets was initially support for multi-GPU configurations with X370. Now that motherboards have been revealed and are up for pre-order now, it turns out that the multi-GPU lines have been blurred a bit. As it stands, both B350 and X370 will support AMD’s CrossFire multi-GPU technology and the X370 alone will also have support for NVIDIA’s SLI technology.

The AM4 motherboards equipped with the B350 and X370 chipsets that feature two PCI-E x16 expansion slots will run as x8 in each slot in a dual GPU setup. (In a single GPU setup, the top slot can run at full x16 speeds.) Which is to say that the slots behave the same across both chipsets. Where the chipsets differ is in support for specific GPU technologies where NVIDIA’s SLI is locked to X370. TechPowerUp speculates that the decision to lock SLI to its top-end chipset is due, at least in part, to licensing costs. This is not a bad thing as B350 was originally not going to support any dual x16 slot multi-GPU configurations, but now motherboard manufacturers are being allowed to enable it by including a second slot and AMD will reportedly permit CrossFire usage (which costs AMD nothing in licensing). Meanwhile the most expensive X370 chipset will support SLI for those serious gamers that demand and can afford it. Had B350 supported SLI and carried the SLI branding, they likely would have been ever so slightly more expensive than they are now. Of course, DirectX 12's multi-adapter will work on either chipset so long as the game supports it.

  X370 B350 A320 X300 / B300 / A300 Ryzen CPU Bristol Ridge APU
PCI-E 3.0 0 0 0 4 20 (18 w/ 2 SATA) 10
PCI-E 2.0 8 6 4 0 0 0
USB 3.1 Gen 2 2 2 1 1 0 0
USB 3.1 Gen 1 6 2 2 2 4 4
USB 2.0 6 6 6 6 0 0
SATA 6 Gbps 4 2 2 2 2 2
SATA RAID 0/1/10 0/1/10 0/1/10 0/1    
Overclocking Capable? Yes Yes No Yes (X300 only)    
SLI Yes No No No    
CrossFire Yes Yes No No    

Multi-GPU is not the only differentiator though. Moving up from B350 to X370 will get you 6 USB 3.1 Gen 1 (USB 3.0) ports versus 2 on B350/A30/X300, two more PCI-E 2.0 lanes (8 versus 6), and two more SATA ports (6 total usable; 4 versus 2 coming from the chipset).

Note that X370, B350, and X300 all support CPU overclocking. Hopefully this helps you when trying to decide which AM4 motherboard to pair with your Ryzen CPU once the independent benchmarks are out. In short, if you must have SLI you are stuck ponying up for X370, but if you plan to only ever run a single GPU or tend to stick with AMD GPUs and CrossFire, B350 gets you most of the way to a X370 for a lot less money! You do not even have to give up any USB 3.1 Gen 2 ports though you limit your SATA drive options (it’s all about M.2 these days anyway heh).

For those curious, looking around on Newegg I notice that most of the B350 motherboards have that second PCI-E 3.0 x16 slot and CrossFire support listed in their specifications and seem to average around $99.  Meanwhile X370 starts at $140 and rockets up from there (up to $299!) depending on how much bling you are looking for!

Are you going for a motherboard with the B350 or X370 chipset? Will you be rocking multiple graphics cards?

Also read:

Acer Announces the Predator 21 X Curved Screen Gaming Notebook

Subject: Systems, Mobile | August 31, 2016 - 10:33 AM |
Tagged: 2560x1080, ips, Predator 21 X, notebook, laptop, gaming, curved, acer, kaby lake, GTX 1080, sli

Acer has announced "the world's first notebook with a curved screen", and this panel happens to be attached to a very high-end gaming laptop in the Predator 21 X.

Predator 21 X_07.jpg

In addition to the 2560x1080 curved 21-inch display, the new machine also offers Tobii eye-tracking technology, Intel 7th Generation "Kaby Lake" processors, and (last but not least) dual NVIDIA GTX 1080 GPUs in SLI.

Predator 21 X_05.jpg

"The Predator 21 X takes the flagship spot in Acer’s gaming notebook series and is advanced beyond anything on the market today. It’s the world’s first notebook to offer a curved 21-inch IPS display (2560 x 1080), and when combined with wide-angle viewing, it delivers a truly immersive gaming experience.

To bring gameplay immersion to the next level, the notebook also integrates Tobii eye-tracking technology for a new method of control that’s more intuitive and natural. Built-in eye-tracking hardware (infrared sensors and software) unlocks a completely new facet in gaming. By tracking a gamer’s eye with software, the notebook introduces new interactions like aiming, identifying enemies and taking cover simply by gazing at objects on the screen. Eye tracking also enhances the experience by providing infinite views whilst navigating treacherous paths and roads in a game."

Other features of the Predator 21 X include a keyboard with Cherry MX key switches, a unique design for the numeric keypad "that allows it to be flipped over and turned into a Precision Touchpad", a 5-fan cooling system, and a 4-speaker, dual-subwoofer premium sound system.

Predator 21 X_08.jpg

Pricing and availability have not been revealed.

Source: Acer
Manufacturer: PC Perspective

Why Two 4GB GPUs Isn't Necessarily 8GB

We're trying something new here at PC Perspective. Some topics are fairly difficult to explain cleanly without accompanying images. We also like to go fairly deep into specific topics, so we're hoping that we can provide educational cartoons that explain these issues.

This pilot episode is about load-balancing and memory management in multi-GPU configurations. There seems to be a lot of confusion around what was (and was not) possible with DirectX 11 and OpenGL, and even more confusion about what DirectX 12, Mantle, and Vulkan allow developers to do. It highlights three different load-balancing algorithms, and even briefly mentions what LucidLogix was attempting to accomplish almost ten years ago.

pcper-2016-animationlogo-multiGPU.png

If you like it, and want to see more, please share and support us on Patreon. We're putting this out not knowing if it's popular enough to be sustainable. The best way to see more of this is to share!

Open the expanded article to see the transcript, below.

Podcast #405 - AMD RX 480 Hands-on, 32-core Zen rumors, VBIOS scandal and more!

Subject: General Tech | June 23, 2016 - 01:02 PM |
Tagged: Zen, western digital, video, vbios, SM961, sli, Samsung, rx 480, radeon, podcast, My Passport Wireless Pro, msi, GTX 1080, evga, drobo, be quiet, asus, amd, 960 PRO

PC Perspective Podcast #405 - 06/23/2016

Join us this week as we discuss an AMD RX 480 hands-on, 32-core Zen rumors, the ASUS/MSI VBIOS scandal and more!

You can subscribe to us through iTunes and you can still access it directly through the RSS page HERE.

The URL for the podcast is: http://pcper.com/podcast - Share with your friends!

This episode of the PC Perspective Podcast is sponsored by Kaspersky Labs!

Hosts:  Ryan Shrout, Allyn Malventano, Jeremy Hellstrom, and Josh Walrath

Program length: 1:33:07
  1. Week in Review:
  2. This episode is sponsored by Kaspersky Labs!
  3. News items of interest:
  4. Hardware/Software Picks of the Week
    1. Allyn: devCalc Pro - Engineering Mode calculator for iOS
  5. Closing/outro

Podcast #403 - Fractal Define S, Corsair Lapdog, Pascal dropping 3+4 way SLI game support, EVGA SLI HB's, and more!

Subject: General Tech | June 9, 2016 - 02:21 PM |
Tagged: Wit.nes, video, technology, SSD 750 M.2, sli, podcast, GTX 1080, gtx 1070, GP104 laptop, Fractal Nano S, fan speed fix, EVGA SLI HB, Corsair SF

PC Perspective Podcast #403 - 06/09/2016

Join us this week as we discuss the Fractal Define S, Corsair Lapdog, Pascal dropping 3+4 way SLI game support, EVGA SLI HB's, and more!

You can subscribe to us through iTunes and you can still access it directly through the RSS page HERE.

The URL for the podcast is: http://pcper.com/podcast - Share with your friends!

This episode of the PC Perspective Podcast is sponsored by Lenovo!

Hosts:  Allyn Malventano, Jeremy Hellstrom, Josh Walrath, and Sebastian Peak

Program length: 1:19:54
  1. Week in Review:
  2. News items of interest:
      1. This is actually in the Mirror’s Edge Driver!
  3. Hardware/Software Picks of the Week
    1. Sebastian: Clean install Windows 8.1 or Windows 10
  4. Closing/outro

GeForce GTX 1080 and 1070 3-Way and 4-Way SLI will not be enabled for games

Subject: Graphics Cards | June 8, 2016 - 08:44 PM |
Tagged: sli, pascal, nvidia, GTX 1080, GP104, geforce, 4-way sli, 3-way sli

IMPORTANT UPDATE: After writing this story, but before publication, we went to NVIDIA for comment. As we were getting ready to publish, the company updated me with a shift in its stance on multi-GPU configurations. NVIDIA will no longer require an "enthusiast key" to enable SLI on more than two GPUs. However, NVIDIA will also only be enabling 3-Way and 4-Way SLI for a select few applications. More details are at the bottom of the story!

You'll likely recall that during our initial review of the GeForce GTX 1080 Founders Edition graphics card, we mentioned that NVIDIA was going to be moving people towards the idea that "only 2-Way SLI will be supported" and promoted. There would still be a path for users that wanted 3 and 4 GPU configurations anyway, and it would be called the Enthusiast Key.

As it turns out, after returning from an AMD event focused on its upcoming Polaris GPUs, I happen to have amassed a total of four GeForce GTX 1080 cards.

01.jpg

Courtesy of some friends at EVGA and two readers that were awesome enough to let me open up their brand new hardware for a day or so, I was able to go through the 3-Way and 4-Way SLI configuration process. Once all four were installed, and I must point out how great it is that each card only required a single 8-pin power connector, I installed the latest NVIDIA driver I had on hand, 368.19.

driver2.jpg

Knowing about the need for the Enthusiast Key, and also knowing that I did not yet have one and that the website that was supposed to be live to enable me to get one is still not live, I thought I might have stumbled upon some magic. The driver appeared to let me enable SLI anyway. 

driver1.jpg

Enthusiasts will note however that the green marker under the four GPUs with the "SLI" text is clearly only pointing at two of the GTX 1080s, leaving the remaining two...unused. Crap.

At this point, if you have purchased more than two GeForce GTX 1080 cards are simply out of luck and are waiting on NVIDIA to make good on it's promise to allow for 3-Way and 4-Way configurations via the Enthusiast Key. Or some other way. It's way too late now to simply say "we aren't supporting it at all." 

03.jpg

While I wait...what is there for a gamer with four GeForce GTX 1080 cards to do? Well, you could run Ashes of the Singularity. It's multi-GPU mode uses MDA mode, which means the game engine itself accesses each GPU on its own, without the need for the driver to handle anything regarding GPU load balancing. Unfortunately, Ashes only supports two GPUs today.

Well...you could run an OpenCL based benchmark like LuxMark that access all the GPUs independently as well.

lux2.jpg

I did so, and the result is an impressive score of 17,127!!

lux.jpg

How does that compare to some other products?

luxmarkgraph.jpg

The four GTX 1080 cards produce a score that is 2.57x the result provided by the AMD Radeon Pro Duo and 2.29x the score of SLI GeForce GTX 980 Ti cards. Nice!

02.jpg

So there you go! We are just as eager to get our hands on the ability to test 3-Way and 4-Way SLI with new Pascal GPUs as some of the most extreme and dedicated enthusiasts out there are. With any luck, NVIDIA will finally figure out a way to allow it - no matter how it finally takes place.

IMPORTANT UPDATE: Before going to press with this story I asked NVIDIA for comment directly: when was the community finally going to get the Enthusiast Key website to unlock 3-Way and 4-Way SLI for those people crazy enough to have purchased that many GTX 1080s? The answer was quite surprising: NVIDIA is backing away from the idea of an "Enthusiast Key" and will no longer require it for enabling 3-Way and 4-Way SLI. 

Here is the official NVIDIA statement given to PC Perspective on the subject:

With the GeForce 10-series we’re investing heavily in 2-way SLI with our new High Bandwidth bridge (which doubles the SLI bandwidth for faster, smoother gaming at ultra-high resolutions and refresh rates) and NVIDIA Game Ready Driver SLI profiles.  To ensure the best possible gaming experience on our GeForce 10-series GPUs, we’re focusing our efforts on 2-way SLI only and will continue to include 2-way SLI profiles in our Game Ready Drivers.
 
DX12 and NVIDIA VR Works SLI technology also allows developers to directly implement and control multi-GPU support within their games.  If a developer chooses to use these technologies then their game will not need SLI profiles.  Some developers may also decide to support more than 2 GPUs in their games. We continue to work with all developers creating games and VR applications that take advantage of 2 or more GPUs to make sure they’ll work great on GeForce 10-series GPUs.
 
For our overclocking community, our Game Ready Drivers will also include SLI profiles for 3- and 4-way configurations for specific OC applications only, including Fire Strike, Unigine and Catzilla.

NVIDIA clearly wants to reiterate that only 2-Way SLI will get the attention that we have come to expect from the GeForce driver dev team. As DX12 and Vulkan next-generation APIs become more prolific, the game developers will still have the ability to directly access more than two GeForce GTX 10-series GPUs, though I expect that be a very narrow window of games simply due to development costs and time.

NVIDIA will enable support for three and four card configurations in future drivers (without a key) for specific overclocking/benchmarking tools only, as a way to make sure the GeForce brand doesn't fall off the 3DMark charts. Only those specific applications will be able operate in the 3-Way and 4-Way SLI configurations that you have come to know. There are no profiles to change manually and even the rare games that might have "just worked" with three or four GPUs will not take advantage of more than two GTX 10-series cards. It's fair to say at this point that except for the benchmarking crowd, NVIDIA 3-Way and 4-Way SLI is over.

We expect the "benchmark only" mode of 3-Way and 4-Way SLI to be ready for consumers with the next "Game Ready" driver release. If you happened to get your hands on more than two GTX 1080s but aren't into benchmarking, then find those receipts and send a couple back.

So there you have it. Honestly, this is what I was expecting from NVIDIA with the initial launch of Pascal and the GeForce GTX 1080/1070 and I was surprised when I first heard about the idea of the "enthusiast key." It took a bit longer than expected, and NVIDIA will get more flak for the iterated dismissal of this very niche, but still pretty cool, technology. In the end, this won't have much impact on the company's bottom line as the quantity of users that were buying 3+ GTX GPUs for a single system was understandably small.

Computex 2016: EVGA Is Making Custom SLI HB Bridges

Subject: Graphics Cards | June 4, 2016 - 02:39 AM |
Tagged: evga, sli, SLI HB, GTX 1080, nvidia, gtx 1070

Still no idea when these are coming out, or how much they'll cost, but EVGA will introduce their own custom SLI High-Bandwidth (HB) bridges. These are designed for the GTX 1080 and GTX 1070 cards in two-way SLI mode to share frames in high-speed 1440p, 4K, 5K, and Surround configurations. As TAP mentioned on our live stream, if the bridge was overloaded, it would fall back to communicating PCIe, which should be doing other things at the time.

nvidia-2016-dreamhack-newsli.png

NVIDIA's SLI HB connector.
We didn't have a presence at Computex, so you'll need to check out Fudzilla's photo for EVGA's.

As for EVGA's model? Without pricing and availability, all we can say is that they have a different aesthetic from NVIDIA's. They also, unlike NVIDIA's version, have RGB LEDs on them to add a splash (or another splash) of colored light inside your case. Three versions will be offered, varying with the distances between your cards, but, as the SLI HB spec demands, each of them only supports two at a time.

Source: Fudzilla

Teaser - GTX 1080's Tested in SLI - EVGA SC ACX 3.0

Subject: Graphics Cards | May 27, 2016 - 02:58 PM |
Tagged: sli, review, led, HB, gtx, evga, Bridge, ACX 3.0, 3dmark, 1080

...so the time where we manage to get multiple GTX 1080's in the office here would, of course, be when Ryan is on the other side of the planet. We are also missing some other semi-required items, like the new 'SLI HB 'bridge, but we should be able to test on an older LED bridge at 2560x1440 (under the resolution where the newer style is absolutely necessary to avoid a sub-optimal experience). That said, surely the storage guy can squeeze out a quick run of 3DMark to check out the SLI scaling, right?

config.png

For this testing, I spent just a few minutes with EVGA's OC Scanner to take advantage of GPU Boost 3.0. I cranked the power limits and fans on both cards, ending up at a stable overclock hovering at right around 2 GHz on the pair. I'm leaving out the details of the second GPU we got in for testing as it may be under NDA and I can't confirm that as all of the people to ask are in an opposite time zone, so I'm leaving out that for now (pfft - it has an aftermarket cooler). Then I simply ran Firestrike (25x14) with SLI disabled:

3dmark-single.png

...and then with it enabled:

3dmark-sli.png

That works out to a 92% gain in 3DMark score, with the FPS figures jumping by almost exactly 2x. Now remember, this is by no means a controlled test, and the boss will be cranking out a much more detailed piece with frame rated results galore in the future, but for now I just wanted to get some quick figures out to the masses for consumption and confirmation that 1080 SLI is a doable thing, even on an older bridge.

*edit* here's another teaser:

heaven-oc-.png

Aftermarket coolers are a good thing as evidenced by the 47c of that second GPU, but the Founders Edition blower-style cooler is still able to get past 2GHz just fine. Both cards had their fans at max speed in this example.

*edit again*

I was able to confirm we are not under NDA on the additional card we received. Behold:

IMG_1692.jpg

IMG_1698.jpg

This is the EVGA Superclocked edition with their ACX 3.0 cooler.

More to follow (yes, again)!

NVIDIA Limits GTX 1080 SLI to Two Cards

Subject: Graphics Cards | May 11, 2016 - 10:57 PM |
Tagged: sli, nvidia, GTX 1080, GeForce GTX 1080

Update (May 12th, 1:45am): Okay so the post has been deleted, which was originally from Chris Bencivenga, Support Manager at EVGA. A screenshot of it is attached below. Note that Jacob Freeman later posted that "More info about SLI support will be coming soon, please stay tuned." I guess this means take the news with a grain of salt until an official word can be released.

evga-2016-gtx1080sli.png

Original Post Below

According to EVGA, NVIDIA will not support three- and four-way SLI on the GeForce GTX 1080. They state that, even if you use the old, multi-way connectors, it will still be limited to two-way. The new SLI connector (called SLI HB) will provide better performance “than 2-way SLI did in the past on previous series”. This suggests that the old SLI connectors can be used with the GTX 1080, although with less performance and only for two cards.

nvidia-2016-dreamhack-newsli.png

This is the only hard information that we have on this change, but I will elaborate a bit based on what I know about graphics APIs. Basically, SLI (and CrossFire) are simplifications of the multi-GPU load-balancing problems such that it is easy to do from within the driver, without the game's involvement. In DirectX 11 and earlier, the game cannot interface with the driver in that way at all. That does not apply to DirectX 12 and Vulkan, however. In those APIs, you will be able to explicitly load-balance by querying all graphics devices (including APUs) and split the commands yourself.

Even though a few DirectX 12 games exist, it's still unclear how SLI and CrossFire will be utilized in the context of DirectX 12 and Vulkan. DirectX 12 has the tier of multi-GPU called “implicit multi-adapter,” which allows the driver to load balance. How will this decision affect those APIs? Could inter-card bandwidth even be offloaded via SLI HB in DirectX 12 and Vulkan at all? Not sure yet (but you would think that they would at least add a Vulkan extension). You should be able to use three GTX 1080s in titles that manually load-balance to three or more mismatched GPUs, but only for those games.

If it relies upon SLI, which is everything DirectX 11, then you cannot. You definitely cannot.

Source: EVGA