The game has changed for SLI. With the RTX 20-series, NVIDIA seems to have reaffirmed their dedication to multi-GPU support with the introduction of NVLink. These new connectors offer more than 12x the bandwidth of last generations’ high-bandwidth bridges on a single link - but the proof is in the pudding. We tested two 2080 Tis to find out. Read on to see the state of SLI at the start of this new generation.
Growing up a techie, SLI was the holy grail of PC gaming. Unfortunately, for most of my life I couldn’t afford it, so I’d stare longingly at those multi-GPU systems and the promises of stunning graphics and amazing performance. For gaming, that was how you achieved the best of the best, better than any console or even “normal” gaming PC.
Over time, the perception began to change. Last generation, people truly began to question whether SLI was even going to be supported in the long-term. I went from dual GTX 580s to dual 1080 Tis but even I had to admit, a lot of it depended on the games you were playing and how patient you were.
That said, let’s dispel a couple of myths, shall we?
Myth the first: Most games don’t support SLI. Outside of the indie space, most games get SLI support, it just might not be there at launch. Wait a couple months, usually less, and it will be there. There are exceptions but anyone repeating this just doesn’t know what they’re talking about. It’s also possible to get custom profiles, but we won’t get into that here.
Myth the second: SLI doesn’t make that big of a difference. Yes, yes it does. Reviews talk about percentages which often obfuscates that you may be getting dozens more frames a second. Is this always the case? No, a lot of it depends on how well it’s implemented, but when people scoff at a 30% improvement, they’re usually doing so because of cost, not impact. Let’s be real, though: if you’re considering SLI, cost probably isn’t your biggest concern anyway. SLI is for the enthusiasts.
Welcome to the next generation of SLI: NVLink
With the RTX 20-series, NVIDIA has officially moved into the next generation of multi-GPU interconnect. As time has gone on, we’ve seen an evolution in SLI, first with our standard flexible SLI bridges and, with the 10-series, rigid PCB high-bandwidth bridges. NVLink, on the other hand, is a massive leap in processing power.
We first saw NVLink at use in NVIDIA’s highest end Quadro cards. NVIDIA GPUs powering supercomputers, neural networks, and artificial intelligence are laced together to scale their performance higher than anything possible in traditional SLI.
Spec-wise, NVLink is features two 8x connections, each capable of 25 GB/sec or 50 GB/sec one way. However, NVLink is a bidirectional interface, bringing the combined bandwidth to an incredible 100 GB/sec. This allows the cards to pool resources in a way that was never before possible. SLI, by contrast, has a roughly 2GB/sec bandwidth and functioned by alternately rendering frames, not truly “doubling up” in the same way NVLink makes possible.
That said, scaling has always been an issue with SLI. Developers still have to properly design their games to take advantage of NVLink and, must like normal SLI, that isn’t and won’t always be the case. Our mission today is to find out right now at launch, how well games are taking advantage of NVLink and perhaps get some hints at what may come in the future.
Test System: i7-8700K at 5GHz, ASUS Maximus X Hero Z470 Motherboard, 32GB ADATA XPG D41 DDR4-3200 DRAM, 1TB Samsung 970 PRO NVME SSD, 1TB WD Black NVME SSD, 1TB WD Blue 2.5” SATA SSD, 1TB Crucial MX500 2.5” SATA SSD, 10TB WD Gold HDD, Corsair HX-1050 1050-watt PSU, Fractal Define R6 Case (open top panel)
To get an idea of generation over generation improvement, we compared two RTX 2080 Tis Founder’s Editions with NVLink to two GTX 1080 Ti’s in SLI. For each test, you’ll see both single card and multi-GPU results to help us determine just how well performance scales with bumped to two cards.
Also note that all game tests were conducted at 4K (3840x2160). While we typically include 1080p and 1440p, it’s likely that anyone considering purchasing two of these flagship cards will already be gaming at 4K resolution. All games are tested at their highest settings with the exception of anti-aliasing and Shadow of the Tomb Raider, which we left on the “High” preset for parity with our previous tests.
We began with synthetic testing using 3DMark Time Spy Extreme. The scaling here is impressive for both the GTX 1080 Ti and RTX 2080 Ti. As you can tell, the near doubling of the score isn’t exactly surprising since that was also the case with the 10-series. It certainly makes you feel good about your investment, though! Since we are looking at graphics power here, we can disregard the slight aberration in the CPU performance.
Looking at sheer frame rate, every single game is performing in the triple digits at 4K, highest settings, sans the aforementioned exceptions. These cards, even as expensive as they are, absolutely open the door to 4K, high refresh rate gaming. While we look at generation over generation improvement, let that sink in: we’ve arrived. 4K HRR gaming is here. Parsing generation over generation improvements can be a little trickier with this style of chart, though, so let’s look at the percentages.
Viewed in this way, it’s a lot easier to see the benefit of NVLink even at this early stage. Depending on the game in our tests, RTX NVLink scaling ranges from 34.5% in our averages all the way to 109.1%, more than doubling the frame rate of a single card! Where things get a little trickier is the 1% lows, which were more neck and neck or even lower than scaling with against our dual 1080 Tis, but again, not in every case.
Looking at the percentages, though, it’s clear that scaling is improved with NVLink, even in games not optimized for it.
What Does This Mean - Discussion
The future of NVLink is in NVIDIA and developer’s hands, but what these results show us is promising. Scaling is definitely improved and when developers optimize for it, the results can be astounding. Seeing the frame rate in Shadow of the Tomb Raider more than double made me cheer out loud. That said, as our results with Battlefield 1 and GTA V show, we’re not all the way there. Developers have to support it and how well they do makes all the difference in scaling performance.
Here’s the thing: that’s always been the case. SLI has always been a game by game success story and yes, there are some games that just won’t support it at all. There’s not way around that. Yet, the results that I’ve formally tested above and my own observations show me that a) out of the box scaling is generally better (sometimes much better) than the 10-series and that when developers do take the time, we should see better scaling than ever before.
Should you buy two GPUs and a $79 NVLink bridge? There’s no escaping the cost here, which makes this a hard sell for anyone but the most strident enthusiast. For nearly $2500, you could buy an entire gaming PC (my first car cost less than $2000). Yet, if you’re the kind of gamer who likes to be on the cutting edge, the kind of gamer who wants to run with “RTX ON” at 4K60+, the kind of gamer who’s seriously going to consider NVLink, this is as good as it gets and the future looks promising indeed.