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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A5 - Sunday, April 3, 2011 - link
I'm guessing Ryan doesn't want to spend a month redoing all of their benchmarks over all the recent cards. Also the only one of your more recent games that would be at all relevant is Shogun 2 - SC2 runs well on everything, no one plays Arma 2, and the rest are console ports...slickr - Sunday, April 3, 2011 - link
apart from Shift, no game is console port.PC only is mafia 2, SC2, Arma 2, shogun 2, dead space is also not a console port. its PC port to consoles.
Ryan Smith - Sunday, April 3, 2011 - link
We'll be updating the benchmark suite in the next couple of months as keeping with our twice a year schedule. Don't expect us to drop Civ V or Crysis, however.Dustin Sklavos - Monday, April 4, 2011 - link
Jarred and I have gone back and forth on this stuff to get our own suite where it needs to be, and the games Ryan's running have sound logic behind them. For what it's worth...Aliens vs. Predator isn't worth including because it doesn't really leverage that much of DX11 and nobody plays it because it's a terrible game. Crysis Warhead STILL stresses modern gaming systems. As long as it does that it'll be useful, and at least provides a watermark for the underwhelming Crysis 2.
Battleforge and Shogun 2 I'm admittedly not sure about, same with HAWX and Shift 2.
Civ 5 should stay, but StarCraft II should definitely be added. There's a major problem with SC2, though: it's horribly, HORRIBLY CPU bound. SC2 is criminally badly coded given how long it's been in the oven and doesn't scale AT ALL with more than two cores. I've found situations even with Sandy Bridge hardware where SC2 is more liable to demonstrate how much the graphics drivers and subsystem hit the CPU rather than how the graphics hardware itself performs. Honestly my only justification for including it in our notebook/desktop suites is because it's so popular.
Mass Effect 2 to Dead Space 2 doesn't make any sense; Dead Space 2 is a godawful console port while Mass Effect 2 is currently one of the best if not THE best optimized Unreal Engine 3 games on the PC. ME2 should get to stay almost entirely by virtue of being an Unreal Engine 3 representative, ignoring its immense popularity.
Wolfenstein is currently the most demanding OpenGL game on the market. It may seem an oddball choice, but it really serves the purpose of demonstrating OpenGL performance. Arma 2 doesn't fill this niche.
Mafia II's easy enough to test that it couldn't hurt to add it.
JarredWalton - Monday, April 4, 2011 - link
Just to add my two cents....AvP is a lousy game, regardless of benchmarks. I also toss HAWX and HAWX 2 into this category, but Ryan has found a use for HAWX in that it puts a nice, heavy load on the GPUs.
Metro 2033 and Mafia II aren't all that great either, TBH, and so far Crysis 2 is less demanding *and* less fun than either of the two prequels. (Note: I finished both Metro and Mafia, and I'd say both rate something around 70%. Crysis 2 is looking about 65% right now, but maybe it'll pick up as the game progresses.)
c_horner - Sunday, April 3, 2011 - link
I'm waiting for the day when someone actually reports on the perceived usability of Mutli-GPU setups in comparison to a single high-end GPU.What I mean is this: often times even though you might be receiving an arbitrarily larger frame count, the lag and overall smoothness of the games aren't anywhere near as playable and enjoyable as a game that can be run properly with a single GPU.
Having tried SLI in the past I was left with a rather large distaste for plopping down the cost of another high end card. Not all games worked properly, not all games scaled well, some games would scale well in the areas it could render easily but minimum frame rates sucked etc. etc. and the list goes on.
When are some of these review sites going to post subjective and real world usage information instead of a bunch of FPS comparisons?
There's more to the story here.
semo - Sunday, April 3, 2011 - link
I think this review covers some of your concerns. It seems that AMD with their latest drivers achieve a better min FPS score compared to nVidia.I've never used SLI myself but I would think that you wouldn't be able to notice the latency due to more than one GPU in game. Wouldn't such latencies be in the micro seconds?
SlyNine - Monday, April 4, 2011 - link
And yet, those micro seconds seemed like macro seconds, Micro studder was one of the most annoying things ever! I hated my 8800GT SLI experience.Haven't been back to multi videocard setups since.
DanNeely - Monday, April 4, 2011 - link
Look at HardOCP.com's reviews. Instead of FPS numbers from canned benches they play the games and list the highest settings that were acceptable. Minimum FPS levels and for SLI/xFire microstuttering problems can push their recommendations down because even when the average numbers look great the situation might actually not be playable.robertsu - Sunday, April 3, 2011 - link
How is microstuttering with 3 GPU's? Is there any in this new versions?