AMD Radeon HD 7970 Review: 28nm And Graphics Core Next, Together As One
by Ryan Smith on December 22, 2011 12:00 AM EST- Posted in
- GPUs
- AMD
- Radeon
- ATI
- Radeon HD 7000
Compute: The Real Reason for GCN
Moving on from our game tests we’ve now reached the compute benchmark segment of our review. While the gaming performance of the 7970 will have the most immediate ramifications for AMD and the product, it is the compute performance that I believe is the more important metric in the long run. GCN is both a gaming and a compute architecture, and while its gaming pedigree is well defined its real-world compute capabilities still need to be exposed.
With that said, we’re going to open up this section with a rather straightforward statement: the current selection of compute applications for AMD GPUs is extremely poor. This is especially true for anything that would be suitable as a benchmark. Perhaps this is because developers ignored Evergreen and Northern Islands due to their low compute performance, or perhaps this is because developers still haven’t warmed up to OpenCL, but here at the tail end of 2011 there just aren’t very many applications that can make meaningful use of the pure compute capabilities of AMD’s GPUs.
Aggravating this some is that of the applications that can use AMD’s compute capabilities, some of the most popular ones among them have been hand-tuned for AMD’s previous architectures to the point that they simply will not run on Tahiti right now. Folding@Home, FLACC, and a few other candidates we looked into for use as compute benchmarks all fall under this umbrella, and as a result we only have a limited toolset to work with for proving the compute performance of GCN.
So with that out of the way, let’s get started.
Since we just ended with Civilization V as a gaming benchmark, let’s start with Civilization V as a compute benchmark. We’ve seen Civilization V’s performance skyrocket on 7970 and we’ve theorized that it’s due to improvements in compute shader performance, and now we have a chance to prove it.
And there’s our proof. Compared to the 6970, the 7970’s performance on this benchmark has jumped up by 58%, and even the previously leading GTX 580 is now beneath the 7970 by 12%. GCN’s compute ambitions are clearly paying off, and in the case of Civilization V it’s even enough to dethrone NVIDIA entirely. If you’re AMD there’s not much more you can ask for.
Our next benchmark is SmallLuxGPU, the GPU ray tracing branch of the open source LuxRender renderer. We’re now using a development build from the version 2.0 branch, and we’ve moved on to a more complex scene that hopefully will provide a greater challenge to our GPUs.
Again the 7970 does incredibly well here compared to AMD’s past architectures. AMD already did rather well here even with the limited compute performance of their VLIW4 architecture, and with GCN AMD once again puts their old architectures to shame, and puts NVIDIA to shame too in the process. Among single-GPU cards the GTX 580 is the closest competitor and even then the 7970 leads it by 72%. The story is much the same for the 7970 versus the 6970, where the 7970 leads by 74%. If AMD can continue to deliver on performance gains like these, the GCN is going to be a formidable force in the HPC market when it eventually makes its way there.
For our next benchmark we’re once again looking at compute shader performance, this time through the Fluid simulation sample in the DirectX SDK. This program simulates the motion and interactions of a 16k particle fluid using a compute shader, with a choice of several different algorithms. In this case we’re using two of them: a highly optimized grid search that Microsoft based on an earlier CUDA implementation, and an (O)n^2 nearest neighbor method that is optimized by using shared memory to cache data.
There are many things we can gather from this data, but let’s address the most important conclusions first. Regardless of the algorithm used, AMD’s VLIW4 and VLIW5 architectures had relatively poor performance in this simulation; NVIDIA meanwhile has strong performance with the grid search algorithm, but more limited performance with the shared memory algorithm. 7970 consequently manages to blow away the 6970 in all cases, and while it can’t beat the GTX 580 at the grid search algorithm it is 45% faster than the GTX 580 with the shared memory algorithm.
With GCN AMD put a lot of effort into compute performance, not only with respect to their shader/compute hardware, but with the caches and shared memory to feed that hardware. I don’t believe we have enough data to say anything definitive about how Tahiti/GCN’s cache compares to Fermi’s cache, this benchmark does raise the possibility that GCN cache design is better suited for less than optimal brute force algorithms. In which case what this means for AMD could be huge, as it could open up new HPC market opportunities for them that NVIDIA could never access, and certainly it could help AMD steal market share from NVIDIA.
Moving on to our final two benchmarks, we’ve gone spelunking through AMD’s OpenCL archive to dig up a couple more compute scenarios to use to evaluate GCN. The first of these is AESEncryptDecrypt, an OpenCL AES encryption routine that AES encrypts/decrypts an 8K x 8K pixel square image file. The results of this benchmark are the average time to encrypt the image over a number of iterations of the AES cypher.
We went into the AMD OpenCL sample archives knowing that the projects in it were likely already well suited for AMD’s previous architectures, and there is definitely a degree of that in our results. The 6970 already performs decently in this benchmark and ultimately the GTX 580 is the top competitor. However the 7970 still manages to improve on the 6970 by a sizable degree, and accomplishes this encryption task in only 65% the time. Meanwhile compared to the GTX 580 it trails by roughly 12%, which shows that if nothing else Fermi and GCN are going to have their own architectural strengths and weaknesses, although there’s obviously some room for improvement.
One interesting fact we gathered from this compute benchmark is that it benefitted from the increase in bandwidth offered by PCI Express 3.0. With PCIe 3.0 the 7970 improves by about 10%, showcasing just how important transport bandwidth is for some compute tasks. Ultimately we’ll reach a point where even games will be able to take full advantage of PCIe 3.0, but for right now it’s the compute uses that will benefit the most.
Our final benchmark also comes from the AMD OpenCL archives, and it’s a variant of the Monte Carlo method implemented in OpenCL. Here we’re timing how long it takes to execute a 400 step simulation.
For our final benchmark the 7970 once again takes the lead. The rest of the Radeon pack is close behind so GCN isn’t providing an immense benefit here, but AMD still improves upon the 6970 by 14%. Meanwhile the lead over the GTX 580 is larger at 33%.
Ultimately from these benchmarks it’s clear that AMD is capable of delivering on at least some of the theoretical potential for compute performance that GCN brings to the table. Not unlike gaming performance this is often going to depend on the task at hand, but the performance here proves that in the right scenario Tahiti is a very capable compute GPU. Will it be enough to make a run at NVIDIA’s domination with Tesla? At this point it’s too early to tell, but the potential is there, which is much more than we could say about VLIW4.
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B3an - Thursday, December 22, 2011 - link
Anyone with half a brain should have worked out that being as this was going to be AMD's Fermi that it would not of had a massive increase for gaming, simply because many of those extra transistors are there for computing purposes. NOT for gaming. Just as with Fermi.The performance of this card is pretty much exactly as i expected.
Peichen - Friday, December 23, 2011 - link
AMD has been saying for ages that GPU computing is useless and CPU is the only way to go. I guess they just have a better PR department than Nvidia.BTW, before suggesting I have suffered brain trauma, remember that Nvidia delivered on Fermi 2 and GK100 will be twice as powerful as GF110
CeriseCogburn - Thursday, March 8, 2012 - link
Well it was nice to see the amd fans with half a heart admit amd has accomplished something huge by abandoned gaming, as they couldn't get enough of screaming it against nvidia... even as the 580 smoked up the top line stretch so many times...It's so entertaining...
CeriseCogburn - Thursday, March 8, 2012 - link
AMD is the dumb company. Their dumb gpu shaders. Their x86 copying of intel. Now after a few years they've done enough stealing and corporate espionage to "clone" Nvidia architecture and come out with this 7k compute.If they're lucky Nvidia will continue doing all software groundbreaking and carry the massive load by a factor of ten or forty to one working with game developers, porting open gl and open cl to workable programs and as amd fans have demanded giving them PhysX ported out to open source "for free", at which point it will suddenly be something no gamer should live without.
"Years behind" is the real story that should be told about amd and it's graphics - and it's cpu's as well.
Instead we are fed worthless half truths and lies... a "tesselator" in the HD2900 (while pathetic dx11 perf is still the amd norm)... the ddr5 "groundbreaker" ( never mentioned was the sorry bit width that made cheap 128 and 256 the reason for ddr5 needs)...
Etc.
When you don't see the promised improvement, the radeonites see a red rocket shooting to the outer depths of the galaxy and beyond...
Just get ready to pay some more taxes for the amd bailout coming.
durinbug - Thursday, December 22, 2011 - link
I was intrigued by the comment about driver command lists, somehow I missed all of that when it happened. I went searching and finally found this forum post from Ryan:http://forums.anandtech.com/showpost.php?p=3152067...
It would be nice to link to that from the mention of DCL for those of us not familiar with it...
digitalzombie - Thursday, December 22, 2011 - link
I know I'm a minority, but I use Linux to crunch data and GPU would help a lot...I was wondering if you guys can try to use these cards on Debian/Ubuntu or Fedora? And maybe report if 3d acceleration actually works? My current amd card have bad driver for Linux, shearing and glitches, which sucks when I try to number crunch and map stuff out graphically in 3d. Hell I try compiling the driver's source code and it doesn't work.
Thank you!
WaltC - Thursday, December 22, 2011 - link
Somebody pinch me and tell me I didn't just read a review of a brand-new, high-end ATi card that apparently *forgot* Eyefinity is a feature the stock nVidia 580--the card the author singles out for direct comparison with the 7970--doesn't offer in any form. Please tell me it's my eyesight that is failing, because I missed the benchmark bar charts detailing the performance of the Eyefinity 6-monitor support in the 7970 (but I do recall seeing esoteric bar-chart benchmarks for *PCIe 3.0* performance comparisons, however. I tend to think that multi-monitor support, or the lack of it, is far more an important distinction than PCIe 3.0 support benchmarks at present.)Oh, wait--nVidia's stock 580 doesn't do nVidia's "NV Surround triple display" and so there was no point in mentioning that "trivial fact" anywhere in the article? Why compare two cards so closely but fail to mention a major feature one of them supports that the other doesn't? Eh? Is it the author's opinion that multi-monitor gaming is not worth having on either gpu platform? If so, it would be nice to know that by way of the author's admission. Personally, I think that knowing whether a product will support multi monitors and *playable* resolutions up to 5760x1200 ROOB is *somewhat* important in a product review. (sarcasm/massive understatement)
Aside from that glaring oversight, I thought this review was just fair, honestly--and if the author had been less interested in apologizing for nVidia--we might even have seen a better one. Reading his hastily written apologies was kind of funny and amusing, though. But leaving out Eyefinity performance comparisons by pretending the feature isn't relative to the 7970, or that it isn't a feature worth commenting on relative to nVidia's stock 580? Very odd. The author also states: "The purpose of MST hubs was so that users could use several monitors with a regular Radeon card, rather than needing an exotic all-DisplayPort “Eyefinity edition” card as they need now," as if this is an industry-standard component that only ATi customers are "asking for," when it sure seems like nVidia customers could benefit from MST even more at present.
I seem to recall reading the following statement more than once in this review but please pardon me if it was only stated once: "... but it’s NVIDIA that makes all the money." Sorry but even a dunce can see that nVidia doesn't now and never has "made all the money." Heh...;) If nVidia "made all the money," and AMD hadn't made any money at all (which would have to be the case if nVidia "made all the money") then we wouldn't see a 7970 at all, would we? It's possible, and likely, that the author meant "nVidia made more money," which is an independent declaration I'm not inclined to check, either way. But it's for certain that in saying "nVidia made all the money" the author was--obviously--wrong.
The 7970 is all the more impressive considering how much longer nVidia's had to shape up and polish its 580-ish driver sets. But I gather that simple observation was also too far fetched for the author to have seriously considered as pertinent. The 7970 is impressive, AFAIC, but this review is somewhat disappointing. Looks like it was thrown together in a big hurry.
Finally - Friday, December 23, 2011 - link
On AT you have to compensate for their over-steering while reading.Death666Angel - Thursday, December 22, 2011 - link
"Intel implemented Quick Sync as a CPU company, but does that mean hardware H.264 encoders are a CPU feature?" << Why is that even a question. I cannot use the feature unless I am using the iGPU or use the dGPU with Lucid Virtu. As such, it is not a feature of the CPU in my book.Roald - Thursday, December 22, 2011 - link
I don't agree with the conclusion. I think it's much more of a perspective thing. Comming from the 6970 to the 7970 it's not a great win in the gaming deparment. However the same can be said from the change from 4870 to 5870 to 6970. The only real benefit the 5870 had over the 4870 was DX11 support, which didn't mean so much for the games at the time.Now there is a new architechture that not only manages to increase FPS in current games, it also has growing potential and manages to excell in the compute field aswell at the same time.
The conclusion made in the Crysis warhead part of this review should therefore also have been highlighted as finals words.