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 - Sunday, April 3, 2011 - link
It took awhile, but we finally have 3 120Hz 1080P monitors on the way. So we'll be able to test Eyefinity, 3D Vision, and 3D Vision Surround; all of which have been neglected around here.Kaboose - Sunday, April 3, 2011 - link
I await these tests with breathless anticipation!veri745 - Sunday, April 3, 2011 - link
While this article was very well written, I think it is hardly worth it without the multi-monitor data. No-one (sane) is going to get 3x SLI/CF with a single monitor, so it's mostly irrelevant.The theoretical scaling comparison is interesting, but I'm a lot more interesting in the scaling at 3240x1920 or 5760x1080.
DanNeely - Sunday, April 3, 2011 - link
This is definitely a step in the right direction; but with other sites having 3x 1920x1200 or even 3x 2560x1600 test setups you'll still be playing catchup.RK7 - Sunday, April 3, 2011 - link
Finally! I created account just to write that comment :) That's what's missing and what definitely needs to be tested! Especially 3D Vision Surround - it's good to know if it's worth to put so much money into such setup, because single card may be on the edge of performance for modern games in stereoscopic mode with single monitor (good example is Metro 2033, that blows mind when in 3D, but I found with single GTX 570@900MHz is playable only at 1600x900 in 3D with maximum settings without DoF and AA, and even in such case it could drop for some action scenes with heavy lighting to ~12 fps...). So if three cards can achieve a good scaling and provide performance per monitor for 3 monitors setup close to single card for one monitor, then we're there and it's worth it definitely, but if numbers will be alike to those for single monitor scaling, then folks should be aware that there's no way for maximum visual quality gaming with current hardware on 3 monitors...Dustin Sklavos - Monday, April 4, 2011 - link
Not completely neglected. I've added triple-monitor surround testing to my boutique desktop reviews whenever able. :)Crazymech - Sunday, April 3, 2011 - link
I'm having my doubts about the capabilities of the 920 OC'd to 3.33 GHz matched up with 3 of the most powerful single GPUs.I understand straying away from SB because of the lanes, but you could at least have upped the OC to 3,8-4, which many people do (and I would think most that considers a tripple setup would use).
To underline it I point to the small differences between the 4.5 GHz 2600K and the lower overclocked one in the boutique builds reviews, with the highest clocked CPU coupled with weaker GPU's nipping at the heels of the more powerful GPU.
I suggest you at least experiment in a single test (say metro for example.. or battlefield) what a higher clocked X58 (or the 980's 6 cores) could do to the setup.
If I'm wrong, it would at least be good to know that.
BrightCandle - Sunday, April 3, 2011 - link
The fact that sandy Bridge has a PCI-E lanes problem is grounds for testing the impact.Still I would rather see the numbers on X58 and triple screen gaming before seeing the impact that SB makes the performance of SLI/CF setups.
Ryan Smith - Sunday, April 3, 2011 - link
For what it's worth, 3.33GHz is actually where this specific 920 tops out. It won't take 3.5GHz or higher, unfortunately.We'll ultimately upgrade our testbed to SNB - this article is the impetus for that - but that's not going to happen right away.
Crazymech - Monday, April 4, 2011 - link
It wont take 3.5? Really? That amazes me.Though very unfortunate for the purpose of this test.
The main focus is (of course) always on how the new GPU in relation to a standard CPU improves the framerate, but once in a while it would be interesting what different CPU's do to the GPU and FPS aswell. Like the old Doom III articles of showing Athlon dominating PenIV.
Thanks for the answer anyhows :).