AMD Radeon HD 7870 GHz Edition & Radeon HD 7850 Review: Rounding Out Southern Islands
by Ryan Smith on March 5, 2012 12:01 AM ESTCompute Performance
Moving on from our look at gaming performance, we have our customary look at compute performance. With GCN AMD significantly overhauled their architecture in order to improve compute performance, as their long-run initiatives rely on GPU compute performance becoming far more important than it is today.
Our first compute benchmark comes from Civilization V, which uses DirectCompute to decompress textures on the fly. Civ V includes a sub-benchmark that exclusively tests the speed of their texture decompression algorithm by repeatedly decompressing the textures required for one of the game’s leader scenes. Note that this is a DX11 DirectCompute benchmark.
The Civ V compute shader benchmark once again shows off just how much the compute shader performance of the 7800 series has improved relative to the 6900 series, with both 7800 cards coming in well, well ahead of any previous generation AMD cards. Compared to NVIDIA’s lineup the 7800 series does fairly well for itself too, although not quite as well as the commanding lead the 7900 series took.
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.
SmallLuxGPU continues to showcase the 7800 series’ improvements over past AMD architectures, and while it’s not the same kind of massive leap we saw with CivV, it’s still enough to bring the 7850 up to near the performance of the 6970, and pushing the 7870 well beyond that. The only real competition here for AMD is AMD.
For our next benchmark we’re looking at 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.
On the one hand, the 7870 gets quite close to the 7950 here in our AESEncryptDecrypt benchmark, in spite of the latter’s higher number of shaders. On the other hand, it’s still not enough to dethrone the GTX 570; the only NVIDIA cards the 7800 series can beat start at the GTX 560 Ti.
Finally, our last benchmark is 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 an (O)n^2 nearest neighbor method that is optimized by using shared memory to cache data.
In our final compute test the 7800 series once again makes a run at the top, with both cards rising past the GTX 570, although they can’t quite match the GTX 580. In an interesting turn of events the 7870 ends up being some 6% faster than the 7950, in spite of the fact that in a compute benchmark the 7950 should have a solid lead. This just goes to show that core clockspeeds do matter, and that adding more shaders alone can’t conquer all benchmarks.
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rburnham - Monday, March 5, 2012 - link
I tend to skip one or two generations of video cards before upgrading, but the 7850 looks like a fairly respectable upgrade over my current 6850. I love that low power draw, although I might wait until someone like MSI comes out with a quieter version.CeriseCogburn - Thursday, March 8, 2012 - link
Your 6850 is 2 watts higher power draw at idle. But you're a gamer, so load draw is important. The 7850 is 14 watts higher power draw on normal load, and 26 watts more on high load. Powertune slider only increases that.smoka - Monday, March 5, 2012 - link
A lot of people are saying power draw is not important, but it is for some of us upgrading. I have been running a GTX460 for about a year now and I'm finally thinking about jumping on the Eyefinity bandwagon. I was eying the 6950 a few weeks ago, but I decided to wait for the 78xx to come out. My plan is to move to a single card and run at a lower resolution (3072x768 or 3840x1024) until I can upgrade to a CF setup and run at 5760x1080.Also keep in mind that I have a 600W PSU, which would need an upgrade a 69xx CF or GTX570/580 SLI setup. Many people who are in the mid-high end gaming market (which the 78xx is aimed at) don't have a 1000W PSU. Upgrading to these top-tier PSUs is also another expense to add to an already expensive graphics card overhaul.
The 7870 series fits the bill exactly for me, except for the $350 price-point. I really wanted the it to be priced at $300 or less. I am hoping it will hit this price either due to brand competition, store promotion, or after kepler release.
kallogan - Monday, March 5, 2012 - link
Actually i care about power consumption more than stupid power hungry raw performance.You are not responsible citizens when buying nvidia stuff. Buy amd and save the planet.
HAHA
compvter - Monday, March 5, 2012 - link
Sure performance/price matters most, but what i find interesting in current amd generation cards is zerocore that allows me to keep my computer running with low power draw when i don't use it. I don't really care about power draw when i am using computer, but i do care about noise, and those are kind of related. Still most of the cards are silent enough for me, but most of the time my coputer is on idle (or long idle) with software running that i can't turn off (irc client), so zerocore would save me a lot of money compared to Nv offerings. Still i am interested to see what nv offers, but at the moment im considering 7870 to replace my 3870x2. Would go 79xx, but don't want to buy new case =/mattgmann - Monday, March 5, 2012 - link
save the planet...lol. Though saving on the electricity bill would be nice. The power hungry 4890 tandem in my rig surely adds a few tens of dollars a month to my bill.pieguy - Monday, March 5, 2012 - link
In the paragraph about 7800 series voltage, you mention 7950 voltages but I think you mean 7850 voltage, else I am not understanding...Also, a question about these voltages of 1.213 - 1.219. I don't know much on the subject. If these are the voltages under load, what are they actually set to (before vdroop)? If this voltage is standard for these cards, does it mean that we shouldn't be concerned about using this voltage on other 28nm 7XXX series cards for extra OC headroom and 24/7 usage? I'm just trying to figure out a max "safe" 24/7 voltage for my 7950 since the overclocking scales really well with voltage increases.
Thanks for the great review!
Ryan Smith - Monday, March 5, 2012 - link
Hi Pie, thanks for the correction. As for the voltages, those are the VIDs, so it's without vdroop. As for what a safe voltage is, there's no easy answer to that. Though 1.21v is likely safe for 7900 cards that are already in the 1.17v range.ObeseMaurice - Monday, March 5, 2012 - link
I bought a 2GB 6950 2 weeks ago for $240 and $20 mail in rebate. The 7870 is worse on all resolutions of Battlefield 3 and priced significantly higher. Very unimpressive product launch from AMD.silverblue - Monday, March 5, 2012 - link
Has anybody stopped to think how much extra performance you might get from these cards when AMD has proper drivers for them, or is this considered a moot point? Needless to say, nowhere on the BF3 benchmarks in this review is the 7870 slower than the 6950, rather it's a consistent 20% faster. Throughout the review the 7870 ranges from about 15% (Batman 1920x1200) - 70% (Civ5 1920x1200) faster depending on the title. Granted, the gap isn't always this large at 2560x1600 but it's still sizeable in a good number of cases. Are you in fact referring to the 7850?AMD are pricing these cards at that level because they can. It's certainly not going to last forever.