A Look At Triple-GPU Performance And Multi-GPU Scaling, Part 1
by Ryan Smith on April 3, 2011 7:00 AM ESTClosing Thoughts
Unlike our normal GPU reviews, looking at multi-GPU scaling in particular is much more about the tests than it is architectures. With AMD and NVIDIA both using the same basic alternate frame rendering strategy, there's not a lot to separate the two on the technology side. Whether a game scales poorly or well has much more to do with the game than the GPU.
| Radeon HD 6970 | GeForce GTX 580 | |||||
| GPUs | 1->2 | 2->3 | 1->3 | 1->2 | 2->3 | 1->3 |
| Average Avg. FPS Gain | 185% | 127% | 236% | 177% | 121% | 216% |
| Average Min. FPS Gain | 196% | 140% | 274% | 167% | 85% | 140% |
In terms of average FPS gains for two GPUs, AMD has the advantage here. It’s not much of an advantage at under 10%, but it is mostly consistent. The same can be said for three GPU setups, where the average gain for a three GPU setup versus a two GPU setup nets AMD a 127% gain versus 121% for NVIDIA. The fact that the Radeon HD 6970 is normally the weaker card in a single-GPU configuration makes things all the more interesting though. Are we seeing AMD close the gap thanks to CPU bottlenecks, or are we really looking at an advantage for AMD’s CrossFire scaling? One thing is for certain, CrossFire scaling has gotten much better over the last year – at the start of 2010 these numbers would not have been nearly as close.
Overall the gains for SLI or CrossFire in a dual-GPU configuration are very good, which fits well with the fact that most users will never have more than two GPUs. Scaling is heavily game dependent, but on average it’s good enough that you’re getting your money’s worth from a second video card. Just don’t expect perfect scaling in more than a handful of games.
As for triple-GPU setups, the gains are decent, but on average it’s not nearly as good. A lot of this has to do with the fact that some games simply don’t scale beyond two GPUs at all – Civilization V always comes out as a loss, and the GPU-heavy Metro 2033 only makes limited gains at best. Under a one monitor setup it’s hard to tell if this is solely due to poor scaling or due to CPU limitations, but CPU limitations alone do not explain it all. There are a couple of cases where a triple-GPU setup makes sense when paired with a single monitor, particularly in the case of Crysis, but elsewhere framerates are quite high after the first two GPUs with little to gain from a 3rd GPU. I believe super sample anti-aliasing is the best argument for a triple-GPU setup with one monitor, but at the same time that restricts our GPU options to NVIDIA as they’re the only one with DX10/DX11 SSAA.
Minimum framerates with three GPUs does give us a reason to pause for a moment and ponder some things. For the games we do collect minimum framerate data for – Crysis and Battlefield: Bad Company 2 – AMD has a massive lead in minimum framerates. In practice I don’t completely agree with the numbers, and it’s unfortunate that most games don’t generate consistent enough minimum framerates to be useful. From the two games we do test AMD definitely has an advantage, but having watched and played a number of games I don’t believe this is consistent for every game. I suspect the games we can generate consistent data for are the ones that happen to favor the 6970, and likely because of the VRAM advantage at that.
Ultimately triple-GPU performance and scaling cannot be evaluated solely on a single monitor, which is why we won’t be stopping here. Later this month we’ll be looking at triple-GPU performance in a 3x1 multi-monitor configuration, which should allow us to put more than enough load on these setups to see what flies, what cracks under the pressure, and whether multi-GPU scaling can keep pace with such high resolutions. So until then, stay tuned.
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Ryan Smith - Monday, April 4, 2011 - link
There are 2 reasons for that:1) We can't immediately get another 6990. I know it seems odd that we'd have trouble getting anything, but vendors are generally uninterested in sampling cards that are reference, which is why we're so grateful to Zotac and PowerColor for the reference 580/6970.
2) We actually can't run a second 6990 with our existing testbed. The Rampage II Extreme only has x16 slots at positions 2 and 4; position 6 is x8. The spacing needs for a 6990CF setup require 2 empty slots, meaning we'd have to install it in position 6. Worse yet is that position 6 is abutted by our Antec 1200W PSU - this isn't a problem with single-GPU cards as the blowers are well clear of the PSU, but a center-mounted fan like the 6990 would get choked just as if there was another card immediately next to it.
We will be rebuilding our testbed for SNB and using a mobo with better spacing, but that's not going to happen right away. The point being that we're not ignoring the 590/6990 multiple card configurations, it's just not something we're in a position to test right now.
piroroadkill - Monday, April 4, 2011 - link
As long as it's in the works, that's alright. Seems like you have your reasons for it being the way it is.Rukur - Monday, April 4, 2011 - link
This whole technology is stupid with monitors.Why don't you stitch together 3 projectors for a seamless canvas to play a game ?
SlyNine - Monday, April 4, 2011 - link
"This whole technology is stupid with monitors." Do you suppose neural interfaces will be her soon. kick ass.Rukur - Monday, April 4, 2011 - link
Can you read more than one sentence ?monkeyshambler - Monday, April 4, 2011 - link
Interesting stuff, but for a 3 card SLI / crossfire what I'd really want to see is what the framerates are when every setting on the card is maxed.e.g. 24x AA 16x AF, high quality settings selected in the driver control panels etc.
supplement this with whats the performance on triple SLI with 3 1920*1080 monitors @ 4x AA
As lets face it if your going to spend this sort of money (and likely a watercooling rig too as theirs no way three cards are tolerable otherwise) you want to have a genuine show of why you should invest.
The current resolutions just will never stretch the cards or enable them to differentiate significantly from a standard SLI setup.
Hope we can see some of the above in a future article....
Rukur - Monday, April 4, 2011 - link
I tend to agree. How is maxing everything any worse then half inch monitor bezels all over your play area.The whole idea of eye infinity is stupid unless we all look through widows with 1 inch gaps while racing extreme cars.
How about some projectors stitched together for real people to actually try.
erple2 - Tuesday, April 5, 2011 - link
Wasn't there an analysis a while back comparing 1x, 2x, 4x, 8x and 16x AA? I thought that the conclusion to that was that there's no discernible difference between 8x and 16x AA, and the differences between 4x and 8x were only visible in careful examination of static images. Under normal play, you couldn't actually tell any difference between them.Maybe I'm just remembering wrong.
Also, I think that Ryan mentioned why they haven't yet done the triple monitor tests yet (lack of hardware).
DanNeely - Tuesday, April 5, 2011 - link
That's generally correct. Toms Hardware has run PCI restriction tests roughly once per GPU generation. The only game that ever really suffered at x4 bandwidth was MS flight simulator.PCIe bandwidth can impact some compute tasks. Einstien@home runs about 30% faster on a 460 in an 16x slot vs an 8x.
fepple - Monday, April 4, 2011 - link
With my two 5870s I have a wierd problem in crossfire. I have two screens a 24''' LCD and a 37'' LED TV. When in crossfire if I play video on the second screen it gets some odd artifacts of black(ish) horizontal lines across the bottom of the screen. Only solution i've found is to not have the cards in crossfire and plug the TV/Screen into different cards for watching stuff.Annoying, any thoughts?