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
Theoreticals & Tessellation
From a rendering perspective one of the most interesting things AMD did with Tahiti was what they didn’t do: they didn’t add more ROPs, they didn’t add more geometry engines. And yet based on our game performance they’ve clearly improved on their performance in those situations by making more efficient use of the hardware they do have.
So we wanted to take a quick look at synthetic performance to see what these tools had to say about AMD’s changes. We’ve included the numbers for every other GPU in our lineup as a reference point, but we would strongly suggest against reading into them too much. AMD versus AMD is sometimes relevant to real world performance; AMD versus NVIDIA rarely is.
We’ll start with 3DMark Vantage and its color fill test. This is basically a ROP test that attempts to have a GPU’s ROPs blend as many pixels as it can. Theoretically AMD can do 32 color operations per clock on Tahiti, which at 925MHz for 7970 means the theoretical limit is 29.6Gpix/sec; not that any architecture is ever that efficient. In practice 7970 hits 13.33Gpix/sec, which is still well short of the theoretical maximum, but pay close attention to 7970’s performance relative to 6970. Even with the same number of ROPs and a similar theoretical performance limit (29.6 vs 28.16), 7970 is pushing 51% more pixels than 6970 is.
In designing Tahiti AMD said that they didn’t need more ROPs they just needed more efficient ROPs, and it looks like they’ve delivered on this. It’s not clear whether this is the limit for efficiency or if AMD can squeeze more out of their ROPs in future designs, but this definitely helps to prove that there’s more to graphics rendering than a large number of functional units.
Our other 3DMark synthetic benchmark is the 3DMark Vantage Texture Blend test, which measures how quickly a GPU can blend multiple FP16 textures. This is more synthetic than most tests because FP16 textures aren’t widely used, but it’s a consistent benchmark.
The theoretical performance improvement from 6970 to 7970 is 40% - 33% more texture units operating at a 5% higher clockspeed. In practice the 7970 exceeds that improvement by increasing texture performance by 46%, meaning the 7970 has benefitted from more than the increase in texture units. Most likely the new cache architecture has further improved the efficiency of the texture units, although the 3DMark texture set is not particularly large.
Moving on, we also wanted to take a look at tessellation. AMD did not increase the theoretical geometry performance of Tahiti as compared to Cayman – both top out at 2 triangles per clock – but AMD has put a lot of effort into improving the efficiency of Tahiti’s geometry units as we’ve seen reflected in our game benchmarks.
Our first tessellation benchmark is the traditional Detail Tessellation sample program from the DirectX SDK. Here we’re looking at tessellation performance as a product of the framerate, testing at tessellation factors 7 (normal) and 15 (max). Traditionally this is a test that has been rather balanced at normal tessellation levels, while NVIDIA cards with their superior geometry throughput have been the top performers at maximum tessellation levels. So it’s all the more interesting when we’ve seen the tables turned; the 7970 is merely competitive with the GTX 580 at normal tessellation levels, but now it’s ahead of the GTX 580 by 24%. More significantly however the 7970 is ahead of the 6970 by 57%.
Our second tessellation benchmark is Unigine Heaven, a benchmark that straddles the line between a synthetic benchmark and a real-world benchmark, as the engine is licensed but no notable DX11 games have been produced using it yet. In any case the Heaven benchmark is notable for its heavy use of tessellation, which means it’s largely a proxy test for tessellation performance.
As with the Detail Tessellation sample program, Heaven shows significant gains for the 7970 versus the 6970, with the 7970 leading by 56%. Meanwhile it leads the GTX 580 by 27%, which is actually slightly better than what we saw under the more “pure” Detail Tessellation sample. Between these two benchmarks it’s clear that AMD’s tessellation efficiency improvements are quite real, and that with Tahiti AMD can deliver much better tessellation performance than Cayman even at virtually the same theoretical triangle throughput rate.
Of course one has to wonder what NVIDIA will have in store for Kepler next year. Their current Fermi design seems to scale well with additional geometry units, but if Tahiti is anything to go by, there’s a great deal to be gained just by focusing on efficiency. NVIDIA has prided themselves on their geometry performance since before GF100 even shipped, so it will be interesting if they have anything in store to hold on to that distinction.
292 Comments
View All Comments
MadMan007 - Thursday, December 22, 2011 - link
More stuff missing on page 9:[AF filter test image] [download table]
Ryan Smith - Thursday, December 22, 2011 - link
Yep. Still working on it. Hold tightMadMan007 - Thursday, December 22, 2011 - link
Np, just not used to seeing incomplete articles publsihed on Anandtech that aren't clearly 'previews'...wasn't sure if you were aware of all the missing stuff.DoktorSleepless - Thursday, December 22, 2011 - link
Crysis won't be defeated until we're able to play at a full 60fps with 4x super sampling. It looks ugly without the foliage AA.Ryan Smith - Thursday, December 22, 2011 - link
I actually completely agree. That's even farther off than 1920 just with MSAA, but I'm looking forward to that day.chizow - Thursday, December 22, 2011 - link
Honestly Crysis may be defeated once Nvidia releases its driver-level FXAA injector option. Yes, FXAA can blur textures but it also does an amazing job at reducing jaggies on both geometry and transparencies at virtually no impact on performance.There's leaked driver versions (R295.xx) out that allow this option now, hopefully we get them officially soon as this will be a huge boon for games like Crysis or games that don't support traditional AA modes at all (GTA4).
Check out the results below:
http://www.hardocp.com/image.html?image=MTMyMjQ1Mz...
AnotherGuy - Thursday, December 22, 2011 - link
If nVidia released this card tomorrow they woulda priced it easily $600... The card succeeds in almost every aspect.... except maybe noise...chizow - Thursday, December 22, 2011 - link
Funny since both of Nvidia's previous flagship single-GPU cards, the GTX 480 and GTX 580, launched for $499 and were both the fastest single-GPU cards available at the time.I think Nvidia learned their lesson with the GTX 280, and similarly, I think AMD has learned their lesson as well with underpricing their HD 4870 and HD 5870. They've (finally) learned that in the brief period they hold the performance lead, they need to make the most of it, which is why we are seeing a $549 flagship card from them this time around.
8steve8 - Thursday, December 22, 2011 - link
waiting for amd's 28nm 7770.this card is overkill in power and money.
tipoo - Thursday, December 22, 2011 - link
Same, we're not going to tax these cards at the most common resolutions until new consoles are out, such is the blessing and curse of console ports.