AMD: It Shouldn’t Be Doing That
As of press time, AMD confirms that the throttling behavior I observed is indeed Tahiti’s thermal protection mechanism in action. However, it claims that Radeon HD 7990 should not be doing this in CrossFire. And yet, it is—we have plenty of GPU-Z logs to illustrate the behavior as it happens.
I have the utmost respect for the company's technical marketing team. They've always been polite, gracious, and helpful. In this case, they earnestly claim the what I'm seeing is not mirrored in their lab. They also say they're seeing up to 1.8x performance scaling with a second card, which would be amazing, given our experiences with scaling beyond two of any GPU. But after testing single- and dual-space setups, reversing case fans to experiment with intake and exhaust, maxing out the speed of the HAF X's coolers, and swapping three different cards around to make sure no one board is unfairly maligned, I don't see any way that my observations can be wrong.
Builders: Is This OK?
Of course, I still didn't want to swear off a product based on a limited number of samples. Editorially, I felt I needed more feedback. In this case, I have three different Radeon HD 7990s that all exhibit the same behavior when they serve as the top card in a CrossFire configuration. But I also wanted to know what some of the boutique system builders were seeing. After all, they cater to many of the same folks that we do. I reached out to Falcon Northwest, Digital Storm, iBuyPower, Origin PC, Maingear, and Puget Systems, asking first if they'd tested two 7990s together, second, if they encountered similar issues, and third, if they would be comfortable selling and guaranteeing hardware that operates at the temperatures I measured.
Jon Bach of Puget Systems was the first to answer back. His team hasn’t seen any demand for single-card 7990-based configs yet, so he didn’t have any data to report on dual-Radeon HD 7990 setups. He did send over thermal measurements for a quad-Radeon HD 7970-based machine in the same HAF X that I’m using, though. By very specifically choosing cards with the right shroud design, he’s able to keep all four GPUs under 80 degrees Celsius. That’s a huge improvement over my experience with two 7990s. If four-way CrossFire is something you simply must have, Jon’s approach is more attractive looking. He's also insistent that temperatures as high as 102 degrees are not acceptable, and expressed concern about long-term reliability. Eighty degrees maximum is the Puget team's guide.
The folks at iBuyPower chimed in next, reporting that dual Radeon HD 7990s are not available due to driver issues encountered during qualification. Additionally, they drew the same conclusion as I did in my launch coverage: 7990s are simply not designed to play well with other components in the same enclosure. Even one Radeon HD 7990 requires a chassis with good airflow.
Kelt Reeves of Falcon Northwest sent out the third (and most detailed) feedback message, stating that Falcon hasn't qualified single- or dual-card Radeon HD 7990 configurations because they failed on the bench. His response warrants a quote:
"For single-card, the issue had to do with the cards warping after heating up, causing their cooling fans to rub on the shroud and creating an awful racket. We don’t know if that issue was limited to our samples, and that probably could’ve been fixed with a retention bracket we asked AMD for. That issue became moot, though, because four-way CrossFire is really the only configuration our clientele want a 7990 for. In a dual-GPU setup, two 7970s are slightly faster and exhaust properly, so they are a better option."
According to Kelt, his team saw the same issues as me, with temperatures as high as 104 degrees. The following picture he took with a thermal camera serves as the perfect illustration of what I was trying to describe.
Kelt continues, "This is only measuring surface temps in an open chassis, but you can clearly see one GPU getting much hotter than the others. This is the GPU that we saw hitting 102+ Celsius. It’s important to note that this hotspot stays where it is, even if you swap the cards. So, the problem is not with a particular 7990, it’s Radeon HD 7990s in CrossFire."
As of press time, I haven't received responses from Digital Storm, Origin PC, or Maingear. Digital Storm does not offer Radeon HD 7990s in CrossFire. Both Origin PC and Maingear do, so they're the two I'd be most interested in hearing feedback from regarding how they combat this in their designs.
Maingear's temp and fan speed chartUpdate, 6/20/13: Just got off the phone with Chris Morley, CTO and VP of technical marketing at Maingear. Chris sent along a graph from data his team generated in Unigine Valley, which he says causes temperatures a degree or two hotter than Heaven. The chart shows the primary card in a CrossFire array topping out at about 85 degrees after 15 minutes, which is interestingly cooler than we saw from a single retail Radeon HD 7990 running Heaven in our own testing. The difference is attributed to a solution put in place by Maingear, though Chris declined to specify the fix. He did acknowledge that there's an airflow issue, that Maingear isn't particularly happy with AMD's design from an integration standpoint, but that the company welcomes the opportunity to address problems like this.
If you have a Maingear Shift with two Radeon HD 7990s, are willing to take a picture of the interior configuration and/or run some thermal data of your own, and shoot it all over to me on Twitter, I'd be happy to add another update with more information.
One Card Or Two? How About None?
A single Radeon HD 7990 has a distinct set of issues. Some can be solved; others cannot. The frame pacing issues pointed out in my launch story may very well be eradicated in the future. But the fact that AMD’s most expensive graphics card jettisons waste heat through its shroud won’t change. And that means you shouldn’t even attempt to cram it into a small form factor enclosure. Assuming a full ATX case, why not snag a pair of 7970s, if that’s the route you want to go? Vanilla (950 MHz) boards are going for as little as $370 each. I can’t think of any situation a single 7990 makes more sense.
That takes us to dual-card configurations. The information we’re bringing to light flat-out kills any reason to pair Radeon HD 7990s up in the same system. And this is the best-case chassis, recommended by AMD. It only get worse/hotter from there. Incidentally, two system builders independently reported that sales of all dual-GPU cards (including GeForce GTX 690) dropped to near-nothing once GeForce GTX Titan showed up. One added that quad-SLI systems based on GTX 690 also put out excessive heat that causes problems in certain cases. It solves these issues by using cases with side-panel intake fans.
Demand for Titan outstripped Nvidia’s ability to produce it. So, there is a healthy market for $1000 video cards. Enthusiasts simply don’t want to spend that much on cards that behave badly—regardless of whether they come from AMD or Nvidia.
Given better dual-card options than one Radeon HD 7990 and technical problems putting two 7990s in the same system, it’s difficult to excuse AMD’s fastest dual-slot card. Not even Bitcoin mining is a good reason to want one. Read All About Bitcoin Mining: Road To Riches Or Fool's Gold? for more information on why.
When it launched, a generous eight-game bundle had me on the fence about the 7990’s prospects. But after spending time evaluating its thermals and acoustics (to say nothing about its crashes and performance hiccups in CrossFire, which could become a story unto itself), I can’t think of one reason to recommend 7990 to a friend. And, at the end of the day, that’s what this job is all about.