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
Tahiti: The First Direct3D 11.1 GPU
One of the many changes coming in Windows 8 next year will be the next iteration of Direct3D, which will be Direct3D 11.1. More so than any other version of Direct3D so far, D3D11.1 is best summed up as a housekeeping release. There will be some new features, but compared to even past point releases such as 10.1 and 9c it’s a small release that’s going to be focusing more on improving the API itself – particularly interoperability with SoC GPUs for Windows 8 – than it will be about introducing new features. This is largely a consequence of the growing length of time for all matters of development hardware and software. By the time Windows 8 ships Direct3D 11 will be 3 years old, but these days that’s shorter than the development period for some AAA games. Direct3D 11/11.1 will continue to be the current Windows 3D API for quite some time to come.
With regards to backward compatibility in D3D11.1, there’s one new feature in particular that requires new hardware to support it: Target Independent Rasterization. As a result AMD’s existing D3D11 GPUs cannot fully support D3D11.1, thereby making Tahiti the first D3D 11.1 GPU to be released. In practice this means that the hardware is once again ahead of the API, even more so than what we saw with G80 + D3D10 or Cypress (5870) + D3D11 since D3D11.1 isn’t due to arrive for roughly another year. For the time being Tahiti’s hardware supports it but AMD won’t enable this functionality until the future – the first driver with D3D11.1 support will be a beta driver for Windows 8, which we expect we’ll see for the Windows 8 beta next year.
So what does D3D11.1 bring to the table? The biggest end user feature is going to be the formalization of Stereo 3D support into the D3D API. Currently S3D is achieved by either partially going around D3D to present a quad buffer to games and applications that directly support S3D, or in the case of driver/middleware enhancement manipulating the rendering process itself to get the desired results. Formalizing S3D won’t remove the need for middleware to enable S3D on games that choose not to implement it, but for games that do choose to directly implement it such as Deus Ex, it will now be possible to do this through Direct3D.
S3D related sales have never been particularly spectacular, and no doubt the fragmentation of the market is partially to blame, so this may be the push in the right direction that the S3D market needs, if the wider consumer base is ready to accept it. At a minimum this should remove the need for any fragmentation/customization when it comes to games that directly support S3D.
With S3D out of the way, the rest of the D3D11.1 feature set isn’t going to be nearly as visible. Interoperability between graphics, video, and compute is going to be greatly improved, allowing video via Media Foundation to be sent through pixel and compute shaders, among other things. Meanwhile target independent rasterization and some new buffer commands should give developers a few more tricks to work with, while double precision (FP64) support will be coming to pixel shaders on hardware that has FP64 support.
Finally, looking at things at a lower level D3D11.1 will be released alongside DXGI 1.2 and WDDM 1.2, the full combination of which will continue Microsoft’s long-term goal of making the GPU more CPU-like. One of Microsoft’s goals has to been to push GPU manufacturers to improve the granularity of GPU preemption, both for performance and reliability purposes. Since XP things have gotten better as Vista introduced GPU Timeout Detection and Recovery (TDR) to reset hung GPUs, and a finer level of granularity has been introduced to allow multiple games/applications to share a GPU without stomping all over each other, but preemption and context switches are still expensive on a GPU compared to a CPU (there are a lot of registers to deal with) which impacts performance and reliability.
To that end preemption is being given a bit more attention, as WDDM 1.2 will be introducing some new API commands to help manage it while encouraging hardware developers to support finer grained preemption. Meanwhile to improve reliability TDR is getting a major addition by being able to do a finer grained reset of the GPU. Currently with Windows 7 a TDR triggers a complete GPU reset, but with Windows 8 and WDDM 1.2 the GPU will be compartmentalized into “engines” that can be individually reset. Only the games/applications using a reset engine will be impacted while everything else is left untouched, and while most games and applications can already gracefully handle a reset, this will further reduce the problems a reset creates by resetting fewer programs.
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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...