ATI Radeon HD 2900 XT: Calling a Spade a Spade
by Derek Wilson on May 14, 2007 12:04 PM EST- Posted in
- GPUs
Texturing, Caches, and Memory
Texturing
R600 features less texture hardware than we would expect to see, though AMD stands by the argument that compute power will come out on top when it matters. At the same time, we can't compute anything if we don't have any data to work with. So let's take a look at what AMD has done with their texture units.
There are four texture units in R600, one for each SIMD unit. These units don't share resources with the hardware in the SIMD units and are independently scheduled by AMD's dispatch processor. The dispatch processor is able to determine what data will be needed for threads about to execute and can handle setting up the texture units without waiting for the SIMD unit to request data and come up empty.
Texture units on the R600 are able to make both filtered and unfiltered texture requests no matter what shader is running. Unfiltered textures are useful with non-image-based texture data like vertex textures, normal maps, and generic blocks of data. Filtered requests will generally be for image data to be used in determining the color of a pixel. R600 can address one unfiltered texture per clock per texture unit and one filtered textures per clock per texture unit. Filtered units can be used to request unfiltered textures if necessary, providing an extra four unfiltered textures in place of one filtered texture.
The unfiltered texture requests will come back through four fp32 texture samplers (one per component), while the filtered requests will return 16 data points which will be run through the texture filtering hardware resulting in four filtered texture samples. The hardware can at best produce 32 single component fp16 unfiltered results per texture unit per clock. More practically, each texture unit can produce four bilinear filtered four component fp16 samples per clock alongside four unfiltered results. For textures with fp32 components, two clocks would be required to complete a bilinear filter process, as only half the data is loaded at a time to conserve bandwidth.
This is definitely a step up for R600, as R5xx hardware doesn't have texture filtering hardware for floating point textures. All told, with each of its four texture units working, R600 can consume up to 32 unfiltered textures or 16 unfiltered textures plus 16 filtered textures (as long as they're fp16 or fewer bits and we're only using bilinear filtering).
G80 is built with four texture address units and eight texture filters per block of 16 SPs. In total, this means NVIDIA's hardware can produce 32 filtered texture samples per clock (again these are fp16 and bilinear filtered). Of course, NVIDIA is operating on twice as many threads per clock, so it is conceivable that they would benefit more from having the extra filtered data.
We will have to wait and see if AMD's approach of providing unfiltered and filtered texture access in parallel pays off. For the general case on pixel shaders, we would want to see more filtered textures per clock, but with vertex and geometry shaders coming into the mix this could be a good way to save hardware space while offering more texturing power. On a final texturing note, AMD implemented "percentage closer" filter hardware for depth stencil textures. This will allow developers to implement fast soft shadows. The details of the implementation weren't indicated though.
Facebook
Twitter
RSS
86 Comments
View All Comments
dragonsqrrl - Thursday, August 25, 2011 - link
You forgot c).-if you're an ATI fanboy
vijay333 - Monday, May 14, 2007 - link
http://www.randomhouse.com/wotd/index.pperl?date=1...">http://www.randomhouse.com/wotd/index.pperl?date=1..."the expression to call a spade a spade is thousands of years old and etymologically has nothing whatsoever to do with any racial sentiment."
strikeback03 - Wednesday, May 16, 2007 - link
What about in Euchre, where a spade can be a club (and vice versa)?johnsonx - Monday, May 14, 2007 - link
Just wait until AT refers to AMD's marketing budget as 'niggardly'...bldckstark - Monday, May 14, 2007 - link
What do shovels have to do with race?Stan11003 - Monday, May 14, 2007 - link
My big hope out all of this that the ATI part forces the Nvidia parts lower so I can use my upgrade option from EVGA to get a nice 8800 GTX instead of my 8800 GTS ACS3 320. However with a quad core and a decent 2GB I have no gaming issues at all. I play at 1600x1200(when that become a low rez?) and everything is butter smooth. Without newer titles all this hardware is a waist anyways.Gul Westfale - Monday, May 14, 2007 - link
the article says that the part is not a failure, but i disagree. i switched from a radeon 1950pro to an nvidia geforce 8800GTS 320MB about a mont ago, and i paid only $350US for it. now i see that it still outperforms the new 2900...one of my friends wanted to wait to buy a new card, he said he hoped that the ATI part was going to be faster. now he says he will just buy the 8800GTS 320, since ATI have failed.
if they can bring out a part that competes well with the 8800GTS and price it similarly or lower then it would be worth buying, but until then i will stick with nvidia. better performance, better price, and better drivers... why would anyone buy the ATI card now?
ncage - Monday, May 14, 2007 - link
My conclusion is to wait. All of the recent GPU do great with dx9...the question is how will they do with dx10? I think its best to wait for dx10 titles to come out. I think crysis would be a PERFECT test.wingless - Monday, May 14, 2007 - link
I agree with you. Crysis is going to be the benchmark for these DX10 cards. Its hard to tell both Nvidia and AMD's DX10 performance with these current, first generation DX10 titles (most of which have a DX9 version) because they don't fully take advantage of all the power on both the G80 or R600 yet. Its true that Crysis will have a DX9 version as well but the developer stated there are some big differences in code. I'm an Nvidia fanboy but I'm disappointed with the Pure Video and HDMI support on the 8800 series cards. ATI got this worked out with their great AVIVO and their nice HDMI implementation but for now Nvidia is still the performance champ with "simpler" hardware. The G80 and R600 continue the traditions of their manufacturers. Nvidia has always been about raw power and all out speed with few bells and whistles. ATI is all about refinement, bells and whistles, innovations, and unproven new methods which may make or break them.All I really want to wait for is to see how developers embrace CUDA or ATI's setup for PHYSICS PROCESSING! Both companies seem to have well thought out methods to do physics and I cant wait to see that showdown. AGEIA and HAVOK need to hop on-board and get some software support for all this good hardware potential they have to play with. Physics is the next big gimmick and you know how much we all love gimmicks (just like good 'ole 3D acceleration 10 years ago).
poohbear - Monday, May 14, 2007 - link
they dont make a profit from high end parts that's why they're not bothering w/ it? that's AMD's story? so why bother having an FX line w/ their cpus?