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
A Quick Refresher: Graphics Core Next
One of the things we’ve seen as a result of the shift from pure graphics GPUs to mixed graphics and compute GPUs is how NVIDIA and AMD go about making their announcements and courting developers. With graphics GPUs there was no great need to discuss products or architectures ahead of time; a few choice developers would get engineering sample hardware a few months early, and everyone else would wait for the actual product launch. With the inclusion of compute capabilities however comes the need to approach launches in a different manner, a more CPU-like manner.
As a result both NVIDIA and AMD have begun revealing their architectures to developers roughly six months before the first products launch. This is very similar to how CPU launches are handled, where the basic principles of an architecture are publically disclosed months in advance. All of this is necessary as the compute (and specifically, HPC) development pipeline is far more focused on optimizing code around a specific architecture in order to maximize performance; whereas graphics development is still fairly abstracted by APIs, compute developers want to get down and dirty, and to do that they need to know as much about new architectures as possible as soon as possible.
It’s for these reasons that AMD announced Graphics Core Next, the fundamental architecture behind AMD’s new GPUs, back in June of this year at the AMD Fusion Developers Summit. There are some implementation and product specific details that we haven’t known until now, and of course very little was revealed about GCN’s graphics capabilities, but otherwise on the compute side AMD is delivering on exactly what they promised 6 months ago.
Since we’ve already covered the fundamentals of GCN in our GCN preview and the Radeon HD 7970 is primarily a gaming product we’re not going to go over GCN in depth here, but I’d encourage you to read our preview to fully understand the intricacies of GCN. But if you’re not interested in that, here’s a quick refresher on GCN with details pertinent to the 7970.
As we’ve already seen in some depth with the Radeon HD 6970, VLIW architectures are very good for graphics work, but they’re poor for compute work. VLIW designs excel in high instruction level parallelism (ILP) use cases, which graphics falls under quite nicely thanks to the fact that with most operations pixels and the color component channels of pixels are independently addressable datum. In fact at the time of the Cayman launch AMD found that the average slot utilization factor for shader programs on their VLIW5 architecture was 3.4 out of 5, reflecting the fact that most shader operations were operating on pixels or other data types that could be scheduled together
Meanwhile, at a hardware level VLIW is a unique design in that it’s the epitome of the “more is better” philosophy. AMD’s high steam processor counts with VLIW4 and VLIW5 are a result of VLIW being a very thin type of architecture that purposely uses many simple ALUs, as opposed to fewer complex units (e.g. Fermi). Furthermore all of the scheduling for VLIW is done in advance by the compiler, so VLIW designs are in effect very dense collections of simple ALUs and cache.
The hardware traits of VLIW mean that for a VLIW architecture to work, the workloads need to map well to the architecture. Complex operations that the simple ALUs can’t handle are bad for VLIW, as are instructions that aren’t trivial to schedule together due to dependencies or other conflicts. As we’ve seen graphics operations do map well to VLIW, which is why VLIW has been in use since the earliest pixel shader equipped GPUs. Yet even then graphics operations don’t achieve perfect utilization under VLIW, but that’s okay because VLIW designs are so dense that it’s not a big problem if they’re operating at under full efficiency.
When it comes to compute workloads however, the idiosyncrasies of VLIW start to become a problem. “Compute” covers a wide range of workloads and algorithms; graphics algorithms may be rigidly defined, but compute workloads can be virtually anything. On the one hand there are compute workloads such as password hashing that are every bit as embarrassingly parallel as graphics workloads are, meaning these map well to existing VLIW architectures. On the other hand there are tasks like texture decompression which are parallel but not embarrassingly so, which means they map poorly to VLIW architectures. At one extreme you have a highly parallel workload, and at the other you have an almost serial workload.
Cayman, A VLIW4 Design
So long as you only want to handle the highly parallel workloads VLIW is fine. But using VLIW as the basis of a compute architecture is going is limit what tasks your processor is sufficiently good at. If you want to handle a wider spectrum of compute workloads you need a more general purpose architecture, and this is the situation AMD faced.
But why does AMD want to chase compute in the first place when they already have a successful graphics GPU business? In the long term GCN plays a big part in AMD’s Fusion plans, but in the short term there’s a much simpler answer: because they have to.
In Q3’2011 NVIDIA’s Professional Solutions Business (Quadro + Tesla) had an operating income of 95M on 230M in revenue. Their (consumer) GPU business had an operating income of 146M, but on a much larger 644M in revenue. Professional products have much higher profit margins and it’s a growing business, particularly the GPU computing side. As it stands NVIDIA and AMD may have relatively equal shares of the discrete GPU market, but it’s NVIDIA that makes all the money. For AMD’s GPU business it’s no longer enough to focus only on graphics, they need a larger piece of the professional product market to survive and thrive in the future. And thus we have GCN.
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Ananke - Thursday, December 22, 2011 - link
"The 7970 leads the 5870 by 50-60% here and in a number of other games"...and as I see it also carries 500-600% of price premium over the 5870.Meh, this is so so priced for a FireGL card, but very badly placed for a consumer market. Regardless, CUDA is getting more open meanwhile. AMD is still several generations/years behind in the HPC market and marketing a product above the NVidia price targets will not help AMD to make it popular.
Having say so, I am using ATI cards for gaming for several years already, and I am very pleased with their IQ and performance. I have always pre-purchased my ATI cards... What I am missing though is teh promised and never materialized consumer level software that can utilize its calculation ability, aka CyberLink and other video transcoders. If it was not for the naughty Nvidia power draw in the 5th series, I would've gone green to have CUDA. Hence, considering SO MUCH MONEY, I am waiting at least 6 months from now to see what the prices will be for the both new contenders in next GPU architectures :).
Dangerous_Dave - Thursday, December 22, 2011 - link
Seems like AMD can't do anything right these days. Bulldozer was designed for a world that doesn't exist, and now we have this new GPU stinking up the place. I'm sorry but @28nm you have double the transistors per area compared with @40nm, yet the performance is only 30% better for a chip that is virtually the same size! It should be at least twice as far ahead of the 6970 as that, even on immature drivers. As it stands, AMD @ 28nm is only just ahead of Nvidia @ 40nm as far as minimums go (the only thing that matters).I shudder to think how badly AMD is going to get destroyed when Nvidia release their 28nm GPU.
Finally - Friday, December 23, 2011 - link
I shudder to think how badly one Nvidia fanboy's ego is going to get scratched if team red released a better GPU and his favourite team has nothing to offer.Oh... they did?
CeriseCogburn - Thursday, March 8, 2012 - link
We have to let amd "go first" now since they have been so on the brink of bankruptcy collapse for so long that they've had to sell off most of their assets... and refinance by AbuDhabi oil money...I think it's nice our laws and global economy puts pressure on the big winners to not utterly crush the underdogs...
Really, if amd makes another fail it might be the last one before collapse and "restructuring" and frankly not many of us want to see that...
They already made the "last move" a dying company does and slashed with the ax at their people...
If the amd fans didn't constantly demand they be given a few dollars off all the time, amd might not be failing - I mean think about it - a near constant loss, because the excessive demand for price vs perf vs the enemy is all the radeon fans claim to care about.
It would be better for us all if the radeon fans dropped the constant $ complaints and just manned up and supported AMD as real fans, with their pocketbooks... instead of driving their favorite toward bankruptcy and cooked books filled with red ink...
Dangerous_Dave - Thursday, December 22, 2011 - link
On reflection this card is even worse than my initial analysis. For 3.4billion transistors AMD could have done no research at all and simply integrated two 6870s onto a single die (a la 5870 vs 4870) and ramped up the clock speed to somewhere over 1Ghz (since 28nm would have easily allowed that). This would have produced performance similar to a 6990, and far in excess of the 7970.Instead we've done a lot of research and spent 4.1billion transistors creating a card that is far worse than a 6990!
That's the value of AMD's creative thinking.
cknobman - Thursday, December 22, 2011 - link
The sad part is your likely too stupid to realize just how idiotic your post sounds.They introduced a new architecture that facilitates much better compute performance as well as giving more gaming performance.
Did you read the article and look at the compute benchmarks or did you just flip through the game benchmark pages and look at numbers without reading?
Zingam - Thursday, December 22, 2011 - link
Or maybe you just don't realize that they've added another 2 billion transistors for minimal graphics performance increase over the previous generation.That's almost as if you buy a new generation BMW that has instead 300 hp, 600hp but is not able to drag a bigger trailer.
The only benefit for you would be that you can brag that you've just got the most expensive and useless car available.
Finally - Friday, December 23, 2011 - link
Rule 1A:The frequency of a car pseudoanalogy to explain a technical concept increases with thread length. This will make many people chuckle, as computer people are rarely knowledgeable about vehicular mechanics.
cknobman - Friday, December 23, 2011 - link
Holy sh!t are you not reading and understanding the article and posts here??????????The extra transistors and new architecture were to increase COMPUTE PERFORMANCE as well as graphics.
Think bigger picture here dude not just games. Think of fusion and how general computing and graphics computing will merge into one.
This architecture is much bigger than just being a graphics card for games.
This is AMD's fermi except they did it about 100x better than Nvidia keeping power in check and still having amazing performance.
Plus your looking at probably beta drivers (heck maybe alpha) so there could very will be another 10+% increase in performance once this thing hit retail shelves and gets some driver improvements.
CeriseCogburn - Thursday, March 8, 2012 - link
I see. So when nvidia did it, it was abandoning gamers for 6 months of ripping away and gnawing plus... but now, since it's amd, amd has done it 100X better... and no abandonment...Wow.
I love hypocrisy in it's full raw and massive form - it's an absolute wonder to behold.