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
Video & Movies: The Video Codec Engine, UVD3, & Steady Video 2.0
When Intel introduced the Sandy Bridge architecture one of their big additions was Quick Sync, their name for their hardware H.264 encoder. By combining a specialized fixed function encoder with some GPU-based processing Intel was able to create a small, highly efficient H.264 encoder that had quality that was as good as or better than AMD and NVIDIA’s GPU based encoders that at the same time was 2x to 4x faster and consumed a fraction of the power. Quick Sync made real-time H.264 encoding practical on even low-power devices, and made GPU encoding redundant at the time. AMD of course isn’t one to sit idle, and they have been hard at work at their own implementation of that technology: the Video Codec Engine (VCE).
The introduction of VCE brings up a very interesting point for discussing the organization of AMD. As both a CPU and a GPU company the line between the two divisions and their technologies often blurs, and Fusion has practically made this mandatory. When AMD wants to implement a feature, is it a GPU feature, a CPU feature, or perhaps it’s both? Intel implemented Quick Sync as a CPU company, but does that mean hardware H.264 encoders are a CPU feature? AMD says no. Hardware H.264 encoders are a GPU feature.
As such VCE is being added to the mix from the GPU side, meaning it shows up first here on the Southern Islands series. Fundamentally VCE is very similar to Quick Sync – it’s based on what you can accomplish with the addition of a fixed function encoder – but AMD takes the concept much further to take full advantage of what the compute side of GCN can do. In “Full Mode” VCE behaves exactly like Quick Sync, in which virtually every step of the H.264 encoding process is handled by fixed function hardware. Just like Quick Sync Full Mode is fast and energy efficient. But it doesn’t make significant use of the rest of the GPU.
Hybrid Mode is where AMD takes things a step further, by throwing the compute resources of the GPU back into the mix. In Hybrid Mode only Entropy Encode is handled by fixed function hardware (this being a highly serial process that was ill suited to a GPU) with all the other steps being handled by the flexible hardware of the GPU. The end goal of Hybrid Mode is that as these other steps are well suited to being done on a GPU, Hybrid Mode will be much faster than even the highly optimized fixed function hardware of Full Mode. Full Mode is already faster than real time – Hybrid Mode should be faster yet.
With VCE AMD is also targeting Quick Sync’s weaknesses regardless of the mode used. Quick Sync has limited tuning capabilities which impacts the quality of the resulting encode. AMD is going to offer more tuning capabilities to allow for a wider range of compression quality. We don’t expect that it will be up to the quality standards of X264 and other pure-software encoders that can generate archival quality encodes, but if AMD is right it should be closer to archival quality than Quick Sync was.
The catch right now is that VCE is so new that we can’t test it. The hardware is there and we’re told it works, but the software support for it is lacking as none of AMD’s partners have added support for it yet. On the positive side this means we’ll be able to test it in-depth once the software is ready as opposed to quickly testing it in time for this review, however the downside is that we cannot comment on the speed or quality at this time. Though with the 7970 not launching until next year, there’s time for software support to be worked out before the first Southern Islands card ever goes on sale.
Moving on, while encoding has been significantly overhauled decoding will remain largely the same. AMD doesn’t refer to the Universal Video Decoder on Tahiti as UVD3, but the specifications match UVD3 as we’ve seen on Cayman so we believe it to be the same decoder. The quality may have been slightly improved as AMD is telling us they’ve scored 200 on HQV 2.0 – the last time we scored them they were at 197 – but HQV is a partially subjective benchmark.
Finally, with Southern Islands AMD is introducing Steady Video 2.0, thesuccessor to Steady Video that was introduced with the Llano APU last year. Steady Video 2.0 adds support for interlaced and letter/pillar boxed content, along with a general increase in the effectiveness of the steadying effect. What makes this particularly interesting is that Steady Video implements a new GCN architecture instruction, Quad Sum of Absolute Differences (QSAD), which combines regular SAD operations with alignment operations into a single instruction. As a result AMD can now execute SADs at a much higher rate so long as they can be organized into QSADs, which is one of the principle reasons that AMD was able to improve Steady Video as it’s a SAD-heavy operation. QSAD extends to more than just Steady Video (AMD noted that it’s also good for other image analysis operations), but Steady Video is going to be the premiere use for it.
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Zingam - Thursday, December 22, 2011 - link
And at the time when it is available in D3D. AMD's implementation won't be compatible... :D That's sounds familiar. So will have to wait for another generation to get the things right.Ryan Smith - Thursday, December 22, 2011 - link
As for your question about FP64, it's worth noting that of the FP64 rates AMD listed for GCN, "0" was not explicitly an option. It's quite possible that anything using GCN will have at a minimum 1/16th FP64.Sind - Thursday, December 22, 2011 - link
Excellent review thanks Ryan. Looking forward to see what the 7950 performance and pricing will end up. Also to see what nv has up their sleeves. Although I can't shake the feeling amd is holding back.chizow - Thursday, December 22, 2011 - link
Another great article, I really enjoyed all the state-of-the-industry commentary more than the actual benchmarks and performance numbers.One thing I may have missed was any coverage at all of GCN. Usually you guys have all those block diagrams and arrows explaining the changes in architecture. I know you or Anand did a write-up on GCN awhile ago, but I may have missed the link to it in this article. Or maybe put a quick recap in there with a link to the full write-up.
But with GCN, I guess we can close the book on AMD's past Vec5/VLIW4 archs as compute failures? For years ATI/AMD and their supporters have insisted it was the better compute architecture, and now we're on the 3rd major arch change since unified shaders, while Nvidia has remained remarkably consistent with their simple SP approach. I think the most striking aspect of this consistency is that you can run any CUDA or GPU accelerated apps on GPUs as old as G80, while you even noted you can't even run some of the most popular compute apps on 7970 because of arch-specific customizations.
I also really enjoyed the ISV and driver/support commentary. It sounds like AMD is finally serious about "getting in the game" or whatever they're branding it nowadays, but I have seen them ramp up their efforts with their logo program. I think one important thing for them to focus on is to get into more *quality* games rather than just focusing on getting their logo program into more games. Still, as long as both Nvidia and AMD are working to further the compatibility of their cards without pushing too many vendor-specific features, I think that's a win overall for gamers.
A few other minor things:
1) I believe Nvidia will soon be countering MLAA with a driver-enabled version of their FXAA. While FXAA is available to both AMD and Nvidia if implemented in-game, providing it driver-side will be a pretty big win for Nvidia given how much better performance and quality it offers over AMD's MLAA.
2) When referring to active DP adapter, shouldn't it be DL-DVI? In your blurb it said SL-DVI. Its interesting they went this route with the outputs, but providing the active adapter was definitely a smart move. Also, is there any reason GPU mfgs don't just add additional TMDS transmitters to overcome the 4x limitation? Or is it just a cost issue?
3) The HDMI discussion is a bit fuzzy. HDMI 1.4b specs were just finalized, but haven't been released. Any idea whether or not SI or Kepler will support 1.4b? Biggest concern here is for 120Hz 1080p 3D support.
Again, thoroughly enjoyed reading the article, great job as usual!
Ryan Smith - Thursday, December 22, 2011 - link
Thanks for the kind words.Quick answers:
2) No, it's an active SL-DVI adapter. DL-DVI adapters exist, but are much more expensive and more cumbersome to use because they require an additional power source (usually USB).
As for why you don't see video cards that support more than 2 TMDS-type displays, it's both an engineering and a cost issue. On the engineering side each TMDS source (and thus each supported TMDS display) requires its own clock generator, whereas DisplayPort only requires 1 common clock generator. On the cost side those clock generators cost money to implement, but using TMDS also requires paying royalties to Silicon Image. The royalty is on the order of cents, but AMD and NVIDIA would still rather not pay it.
3) SI will support 1080P 120Hz frame packed S3D.
ericore - Thursday, December 22, 2011 - link
Core Next: It appears AMD is playing catchup to Nvidia's Cuda, but to an extent that halves the potential performance metrics; I see no other reason why they could not have achieved at varying 25-50% improvement in FPS. That is going to cost them, not just for marginally better performance 5-25%, but they are price matching GTX 580 which means less sales though I suppose people who buy 500$ + GPUs buy them no matter what. Though in this case, they may wait to see what Nvidia has to offer.Other New AMD GPUs: Will be releasing in February and April are based on the current architecture, but with two critical differences; smaller node + low power based silicon VS the norm performance based silicon. We will see very similar performance metrics, but the table completely flips around: we will see them, cheaper, much more power efficient and therefore very quiet GPUs; I am excited though I would hate to buy this and see Nvidia deliver where AMD failed.
Thanks Anand, always a pleasure reading your articles.
Angrybird - Thursday, December 22, 2011 - link
any hint on 7950? this card should go head to head with gtx580 when it release. good job for AMD, great review for Ryan!ericore - Thursday, December 22, 2011 - link
I should add with over 4 billion transistors, they've added more than 35% more transistors but only squeeze 5-25% improvement; unacceptable. That is a complete fail in that context relative to advancement in gaming. Too much catchup with Nvidia.Finally - Thursday, December 22, 2011 - link
...that saying? It goes like this:If you don't show up for a race, you lose by default.
Your favourite company lost, so their fanboys may become green of envydia :)
Besides that - I'd never shell out more than 150€ for a petty GPU, so neither company's product would have appealed to me...
piroroadkill - Thursday, December 22, 2011 - link
Wait, catchup? In my eyes, they were already winning. 6950 with dual BIOS, unlock it to 6970.. unbelievable value.. profit??Already has a larger framebuffer than the GTX580, so...