ATI's X8xx CrossFire Graphics Arrive
by Derek Wilson on September 26, 2005 1:00 PM EST- Posted in
- GPUs
Mode and Hardware Scaling
There are two scaling factors we want to pay attention to here. First, we will be looking at how CrossFire scales with AA mode. As 8x and 10x share the same performance numbers (as do 12x and 14x), we will be looking at: no AA, 4xAA, 6xAA, 10xAA, 12xAA modes. We will be able to see just how steeply Super AA modes drop off in this test.We will also be looking at single card performance. It will be important to compare these numbers to the Super AA numbers, as each card in Crossfire mode should ideally be able to render the entire scene at single card speeds. Any difference between the Super AA modes and a single card running at either 4x or 6x AA account for the overhead of the communication system and compositing engine. The performance drop in these modes is more pronounced than in the other modes, as each card needs to render the entire scene at full frame rate. Any latency or bandwidth limitations will show up more easily here.
Our graphs show frames per second on the y-axis and AA mode across the x-axis.
Doom 3 shows a good performance increase due to CrossFire at standard AA settings. Both the single card and CrossFire setup are similarly GPU limited as AA increases. The drop from 4xAA on a single card to 10xAA on CrossFire is nearly 50%.
When we take a look at Half-Life 2, we see that a single card is fairly GPU limited with increasing AA while CrossFire handles it well. Going from single card AA modes to CrossFire Super AA modes shows more than a 50% drop in performance. This is likely due to the fact that as framerate increases, the impact of latency and bandwidth restrictions on transferring fully antialiased scenes from the slave to the master is proportionally greater.
Here's a look at how going from a single to a two card configuration scales under NVIDIA and ATI hardware under the games we tested.
| Multi GPU % Performance Improvement (16x12 noAA) | |||
| Doom 3 | Battlefield 2 | Half-Life 2 | |
| CrossFire | 41.3 | 53.8 | 15.8 |
| SLI | 34.0 | 89.3 | 22.2 |
| Multi GPU % Performance Improvement (16x12 4xAA) | |||
| Doom 3 | Battlefield 2 | Half-Life 2 | |
| CrossFire | 69.2 | 63.6 | 35.5 |
| SLI | 81.3 | 89.3 | 68.8 |
While Crossfire performs reasonably well without AA, the 4xAA modes show that SLI provides better scaling. More importantly, though, the lack of support for higher resolutions - as well as 1600x1200 at higher refresh rates - becomes a serious limitation of Crossfire. 7800 GTX SLI running at 2048x1536 has no competition from any ATI configuration for the time being.
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Dangher - Monday, September 26, 2005 - link
Good point. Why are comparing previous gen ATI to current gen nVidia?Pythias - Monday, September 26, 2005 - link
Good point. Why are comparing previous gen ATI to current gen nVidia?----------------------------------------------------------------------------------------
Previous gen? I can buy something better than an x850 xt pe from ati? Where?
Dangher - Monday, September 26, 2005 - link
Forgot to add - when it even manages to beat GTX SLI in a benchie (something to think about, eh?)Live - Monday, September 26, 2005 - link
Crossfire is compared to the 6800 Ultra SLI and more. More is better me thinks.If they hadn’t tested it against 7800GTX we would not have know that SLI got beat in HL2, now would we? I think the choice on which cards to test was great.
It's not ATs fault ATI didn’t give them any newer cards to run. You will see those benches next week.
melgross - Monday, September 26, 2005 - link
With the first comparison images between the various levels of AA, I can see the straight picture to be badly stairstepped. The 4AA seems to correct pretty much all of the problems. I can't see a real improvement in any of the others.I wonder how many will notice any of it in an actual game situation.
DerekWilson - Monday, September 26, 2005 - link
It would be easier to show the advantages if I could show motion. Higher AA not only helps the stair steps, but it also helps keep objects that are well antialised in a single frame consistent across multiple frames of motion.Jojo7 - Monday, September 26, 2005 - link
Derek, I've noticed something odd in the last few articles regarding splinter cell:chaos theory and the 6800u benchmarks. If you compare the results of 1600x1200 no aa and 1600x1200 4x aa, the performance hit for the 6800u is .1 of a frame? How is this possible? In my own experience, when I enable 4xaa on my 6800u for sc:ct, I notice no difference in image quality. Is this perhaps a driver problem?Jojo7 - Monday, September 26, 2005 - link
Err. I made a mistake. Actually the scores are identical (40.2) with and without 4xAA.Something has to be wrong here.
DerekWilson - Monday, September 26, 2005 - link
Something is wrong there ... I'm removing the 6800 ultra numbers from sc3 -- thanks for pointing out the problem.erinlegault - Monday, September 26, 2005 - link
Were you a little rush to get this article out of the door?