AMD’s Radeon HD 5850: The Other Shoe Drops
by Ryan Smith on September 30, 2009 12:00 AM EST- Posted in
- GPUs
Battleforge: The First DX11 Game
As we mentioned in our 5870 review, Electronic Arts pushed out the DX11 update for Battleforge the day before the 5870 launched. As we had already left for Intel’s Fall IDF we were unable to take a look at it at the time, so now we finally have the chance.
Being the first DX11 title, Battleforge makes very limited use of DX11’s features given that the hardware and the software are still brand-new. The only thing Battleforge uses DX11 for is for Compute Shader 5.0, which replaces the use of pixel shaders for calculating ambient occlusion. Notably, this is not a use that improves the image quality of the game; pixel shaders already do this effect in Battleforge and other games. EA is using the compute shader as a faster way to calculate the ambient occlusion as compared to using a pixel shader.
The use of various DX11 features to improve performance is something we’re going to see in more games than just Battleforge as additional titles pick up DX11, so this isn’t in any way an unusual use of DX11. Effectively anything can be done with existing pixel, vertex, and geometry shaders (we’ll skip the discussion of Turing completeness), just not at an appropriate speed. The fixed-function tessellater is faster than the geometry shader for tessellating objects, and in certain situations like ambient occlusion the compute shader is going to be faster than the pixel shader.
We ran Battleforge both with DX10/10.1 (pixel shader SSAO) and DX11 (compute shader SSAO) and with and without SSAO to look at the performance difference.
Update: We've finally identified the issue with our results. We've re-run the 5850, and now things make much more sense.
As Battleforge only uses the compute shader for SSAO, there is no difference in performance between DX11 and DX10.1 when we leave SSAO off. So the real magic here is when we enable SSAO, in this case we crank it up to Very High, which clobbers all the cards as a pixel shader.
The difference from in using a compute shader is that the performance hit of SSAO is significantly reduced. As a DX10.1 pixel shader it lobs off 35% of the performance of our 5850. But calculated using a compute shader, and that hit becomes 25%. Or to put it another way, switching from a DX10.1 pixel shader to a DX11 compute shader improved performance by 23% when using SSAO. This is what the DX11 compute shader will initially be making possible: allowing developers to go ahead and use effects that would be too slow on earlier hardware.
Our only big question at this point is whether a DX11 compute shader is really necessary here, or if a DX10/10.1 compute shader could do the job. We know there are some significant additional features available in the DX11 compute shader, but it's not at all clear on when they're necessary. In this case Battleforge is an AMD-sponsored showcase title, so take an appropriate quantity of salt when it comes to this matter - other titles may not produce similar results
At any rate, even with the lighter performance penalty from using the compute shader, 25% for SSAO is nothing to sneeze at. AMD’s press shot is one of the best case scenarios for the use of SSAO in Battleforge, and in the game it’s very hard to notice. For the 25% drop in performance, it’s hard to justify the slightly improved visuals.
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silverblue - Wednesday, September 30, 2009 - link
nVidia shouldn't "get out of the game" at all. True, ATI may just have 3 or 4 months of technical superiority, but nVidia's next cards may be superior as well as offering plenty of revolutionary features.nVidia can also chop prices for their current lineup but not too much, otherwise they may undercut their new cards.
I'm impressed by the 5850's frugal (as compared to the 5870) power requirements. Coupled with a relatively low price, it should sell very nicely indeed (and spawn some overclocked versions very quickly).
SJD - Wednesday, September 30, 2009 - link
Did you have the August DirectX Redist installed on your test system? I think I've read somewhere that this is the update that brings 'full' DirectX11 functionality to Windows 7, and perhaps this is the reason you didn't see the results you were expecting.Otherwise, awesome card!
Ryan Smith - Wednesday, September 30, 2009 - link
Based on AMD's internal data I suspect it's just the fact that we have everything cranked up. We're taking a look at it ASAP.Totally - Wednesday, September 30, 2009 - link
Ryan, could you retest the 5870 again but this time with a piece of tape running across the two 'vents' on the back of the card.Ryan Smith - Wednesday, September 30, 2009 - link
I'm curious what makes you think that will have any impact.Totally - Wednesday, September 30, 2009 - link
well, since it's a centrifugal fan, it sucks air through the center and exhausts it in a radial direction, being the shroud's job to redirect the air afterwards. now looking at how restricted the openings appear on the 5850 and the cooling performance. I'm curious if there is connection, say fresh air may be escaping through those openings and back into the case instead of passing through the heatsink and out the back of the case.Ryan Smith - Wednesday, September 30, 2009 - link
I don't have a good front-shot, but it's a sealed shroud. There's no air escaping.toast70 - Wednesday, September 30, 2009 - link
With 5870 being basically a doubled up 4870 architecture and (still SIMD), i am interested to see how Nvidia's new MIMD architecture will compete, especially with the ridiculous memory bandwidth it will have with GDDR5 and a 512 bit bus.(if the 512 bus isnt just a rumor and hopefully they are not plagued by driver issues) I am glad AMD/ATI is doing better the competition is great, but i feel the new NV cards are going to be good (least if any of the rumors are true). I am still trying to find a reason to replace my 9800GTX SLI, they burn thru about any game as long as you stay away from over 4X AA due to the 512 MB frame buffer.BTW, Not a NV fanboi here, hope i dont sound like one, its late and i just dropped my friend off at the ER, brain is tired. the fiancee's PC has a ATI card and its great, no complaints other than a few driver issues, but nothing i could complain about really. HD4850 512MB
keep up the competition, we have AMD to thank for under 400 fast cards
poohbear - Wednesday, September 30, 2009 - link
very well done review and the conclusion was spot on! gonna get one of these this fall, Nvidia better hurry up b4 shiat really hits the fan.:0Roland00 - Wednesday, September 30, 2009 - link
I wonder how close the 5850 will be to the 5870 once they have similar memory speeds and thus bandiwidth. Are those extra shaders/core frequency wasted due to the limited memory bandiwidth.