AMD CrossFireX and Nvidia SLI Scalability by Radeon HD 6970 and GeForce GTX 570

In our today’s article we are going to learn which of these multi-processor technologies provides maximum performance gain compared with a single graphics accelerator and what obstacles the users may face in either case.

by Sergey Lepilov
03/10/2011 | 11:23 AM

At the end of the last year we tested AMD’s Radeon HD 6850 and HD 6870 graphics cards in CrossFireX mode and were impressed with the performance increase of such configurations over respective single cards which amounted up to 100%. AMD did in fact make it clear that they had overhauled their multi-GPU technology in the new Barts and Cayman processors not only on the software but also on the hardware level, so CrossFireX configurations could indeed be expected to work more effectively across more games and 3D benchmarks. We checked this out with the mentioned cards but what about AMD's top-of-the-line single-chip product Radeon HD 6970? Will it be that effective in a CrossFireX configuration and what will the temperature of two such graphics cards, installed next to each other into a system case, be? We will try to answer these questions in this review. For our testing to be not so narrowly focused and have a competitive streak, we will also add the results of Nvidia GeForce GTX 570s in single-card and SLI modes. Thus, we will see how the multi-GPU technologies from Nvidia and AMD compare in terms of efficiency.

Testbed and Methods

 

All graphics cards were benchmarked in a closed system case with the following configuration:

In order to lower the dependence of the graphics cards performance on the overall platform speed, I overclocked our 32 nm six-core CPU with the multiplier set at 24x and “Load-Line Calibration” (Level 2) enabled to 4.5GHz. The processor Vcore was increased to 1.475V in the mainboard BIOS:

The 6 GB of system DDR3 memory worked at 1.5 GHz frequency with 7-7-7-16_1T timings and 1.64V voltage. Turbo Boost and Hyper-Threading technologies were disabled during our test session.

AMD Radeon HD 6970 graphics cards are the reference ones. They work at nominal clock frequencies. However, both Nvidia GeForce GTX 570 graphics cards are also designed following the reference layout, but one of the cards worked at OC frequencies, so we had to adjust them to the nominal level before starting the tests:

 

 

The test session started on February 19, 2011. All tests were performed in Microsoft Windows 7 Ultimate x64 with all critical updates as of that date and the following drivers:

The graphics cards were tested in games in two currently most popular resolutions: 1920x1080 and 2560x1600. The tests were performed in two image quality modes: “High Quality+AF16x” – maximum texturing quality with enabled 16x anisotropic filtering and “High Quality+ AF16x+AA4(8)x” with enabled 16x anisotropic filtering and 4x full screen anti-aliasing (MSAA) or 8x if the average framerate was high enough for comfortable gaming experience. We enabled anisotropic filtering and full-screen anti-aliasing from the game settings or configuration files. If the corresponding options were missing, we changed these settings in the Control Panel of Catalyst and GeForce/ION drivers. Vertical sync was always off in driver control panels.

The benchmarking games and applications list has been updated minimally since our last review. Besides the usual patches updates for synthetic benchmarks, we recorded a new test scene for Left 4 Dead 2 game (d60), and used a new test scene B instead of the previously used test scene A. Moreover, we have temporarily added a beta version of the new Crysis 2 game, which will be replaced with a full game version as soon as it becomes available. Unfortunately, Crysis 2 only supports DirectX 9 for now.

So, the complete list of test applications included two popular semi-synthetic benchmarking suites, one technical demo and 18 games of various genres. Here is the complete list of tests used with the settings (all games listed in their release order):

If the game allowed recording the minimal fps readings, they were also added to the charts. We ran each game test or benchmark twice and took the best result for the diagrams, but only if the difference between them didn’t exceed 1%. If it did exceed 1%, we ran the tests at least one more time to achieve repeatability of results.

Performance

The results of the AMD Radeon HD 6970 cards are red in the diagrams. The Nvidia GeForce GTX 570s are traditionally green. Let’s now take a look at the numbers.

3DMark Vantage

The Radeon HD 6970 pair doesn’t boast high scalability compared to the single card and is also inferior to the GeForce GTX 570 SLI configuration. The gap is rather large in the FSAA-less mode although a GTX 570 is cheaper than an HD 6970.

3DMark 2011

The new version of the benchmarking suite has a different picture to show us: the two Radeon HD 6970s outperform the single such card by 83% and more. The GeForce GTX 570 SLI, on its part, is faster than the single GTX 570 by 77% and more. As a result, the multi-GPU tandems from AMD and Nvidia are roughly equal to each other in this test.

Unigine Heaven Demo

Unigine Heaven allows the CrossFireX configuration to be 93% to 105% faster than the single Radeon HD 6970. That’s excellent scalability, yet AMD’s solution is inferior to the GeForce GTX 570 both in single-card and multi-GPU modes, although the performance boost of the GeForce GTX 570 SLI is only 77% and 87% compared to the single such card. Nvidia’s product seems to cope better than AMD’s with the extremely high-level tessellation this test makes use of.

Crysis

The scalability of the Radeon HD 6970 CrossFireX subsystem varies from 63% to 100% (at 2560x1600 in the high-quality mode). As a result, the Radeon HD 6970 tandem is somewhat faster than the GeForce GTX 570 SLI although the respective single cards deliver the same performance in Crysis.

Far Cry 2

The Radeon HD 6970 shows high scalability in Far Cry 2 as well, being 81% and further ahead of the single card. The GeForce GTX 570 is somewhat faster than the AMD solution in every mode and configuration here, but Far Cry 2 doesn’t really need more than one fast graphics card to run at a playable speed even at the highest quality settings.

BattleForge: Lost Souls

The multi-GPU configurations from both AMD and Nvidia are excellent in terms of scalability in BattleForge: Lost Souls. Their performance increase is 88% and higher, which is a very good result for top-end graphics cards. The competitors are roughly equal across all the display modes, yet the GeForce GTX 570 is somewhat faster when we turn on full-screen antialiasing. It must be noted that the game’s system requirements are high and the CrossFireX and SLI tandems are going to be very useful for playing it with comfort.

Resident Evil 5

The GeForce GTX 570s win this test but, returning to the subject of this review, we can see that in the FSAA-less mode the scalability of the CrossFireX configuration varies from 62% to 74% whereas the scalability of the SLI tandem is 72% to 86%. When we turn FSAA on, the CrossFireX configuration offers higher scalability (83 to 88%) compared to the SLI one (73% to 81%). That’s good, but Nvidia’s solution is still faster.

S.T.A.L.K.E.R.: Call of Pripyat

Nvidia wins in S.T.A.L.K.E.R., too. Despite the performance benefits of the Radeon HD 6970 tandem over the single such card (40% at 1920x1080 and 60% at 2560x1600), the problem with CrossFireX in this game is that the bottom speed, which is the crucial factor for player’s comfort, is too low. Unfortunately, the two Radeon HD 6970s do not run S.T.A.L.K.E.R. as smoothly as the GeForce GTX 570s which is indicated by the difference in their bottom speeds. Nvidia’s multi-GPU solution enjoys a higher increase in average frame rate, too.

Borderlands: The Secret Armory of General Knoxx

Like in the previous test, the CrossFireX tandem does not enjoy a high advantage over the single card in terms of the average frame rate whereas its bottom speed is downright low. On the other hand, the GeForce GTX 570 pair is far from brilliant in this game, too.

Grand Theft Auto IV: Episodes from Liberty City

This game's engine doesn't like multi-GPU technologies much. As you can see, CrossFireX and SLI can only increase the average frame rate by 32 to 57%, which is hardly a strong argument in favor of buying a second card specifically for Grand Theft Auto IV.

Left 4 Dead 2: The Sacrifice

It’s all simple in this game: the heavier the graphics load, the higher the scalability of the multi-GPU technologies. The solutions from AMD and Nvidia are roughly equal to each other in this game but we must admit that Left 4 Dead 2 runs fast even on a single top-end graphics card at 2560x1600 with 8x FSAA.

Metro 2033: The Last Refuge

We would commend both multi-GPU technologies in Metro 2033: The Last Refuge (their scalability amounts to about 70%) if the bottom speeds were not so low. We cannot achieve a bottom speed of 20 fps on the Radeon HD 6970 CrossFireX or on the GeForce GTX 570 SLI here.

Just Cause 2

The graphics solutions from AMD and Nvidia deliver the same speed in single-GPU mode and offer the same scalability of the multi-GPU configurations. We must note that this game really calls for a multi-GPU subsystem if you want to play it at a high resolution with FSAA.

Aliens vs. Predator (2010)

Like in the previous game, the solutions from AMD and Nvidia are equals but both multi-GPU technologies are more effective than in Just Cause 2, boasting a performance increase up to 100% over the single card.

Lost Planet 2

As opposed to the two previous games, Lost Planet 2 is not so enthusiastic about the multi-GPU technologies. The performance growth varies from 55% to 77%. We can note that CrossFireX is less effective than SLI and that the Nvidia solutions are superior to the AMD ones in this game both in single-GPU and multi-GPU modes.

StarCraft 2: Wings of Liberty

Multi-GPU technologies can only make sense in StarCraft 2: Wings of Liberty if that’s Nvidia SLI and if you are going to use FSAA. Despite the unimpressive scalability over the single card, the GeForce GTX 570 tandem feels better in this test than the Radeon HD 6970 CrossFireX. The latter configuration gets awfully slow when we turn on FSAA.

Mafia 2

SLI technology has higher scalability in Mafia 2 than CrossFireX. As a result, the GeForce GTX 570 pair is as fast as the Radeon HD 6970 tandem and even faster at 1920x1080, although the Radeon wins in single-card mode.

Sid Meier’s Civilization V

Here, the AMD solutions are superior to the Nvidia ones in single-card mode as well as in terms of scalability of multi-GPU technologies.

F1 2010

Like in the previous test, the scalability of the CrossFireX tandem is higher than that of the SLI configuration, so the Radeon HD 6970s gain the upper hand. However, the CrossFireX subsystem is only 75% faster than the single HD 6970. Its bottom speed is high but this must be due to the game engine rather than to the graphics cards or multi-GPU technologies.

Tom Clancy’s H.A.W.X. 2

The Radeon HD 6970 CrossFireX is 83 to 95% faster than the single such card in this game, which is a very good result. On the other hand, the Nvidia solutions are superior to the AMD ones in every test mode and configuration here.

Crysis 2 beta

The beta version of Crysis 2 does not support DirectX 10 and 11 and is also incompatible with multi-GPU technologies. It doesn’t support FSAA, either. So, there is nothing to comment upon except that the Radeon cards have a lower bottom speed than the GeForces. Hopefully, the game will have become far friendlier to CrossFireX and SLI by the time of its release.

Performance Summary

Here is a table with the results of our tests. We can proceed to the summary diagrams now.

The first two pairs of summary diagrams allow us to compare the efficiency of AMD CrossFireX and Nvidia SLI technologies with respect to Radeon HD 6970 and GeForce GTX 570 graphics cards in all the games and graphics quality modes. First, here are the results without FSAA.

CrossFireX has higher efficiency than SLI in two out of the three semi-synthetic benchmarks, SLI winning in 3DMark Vantage only. AMD’s technology is also more effective in such games as Crysis, Far Cry 2, Aliens vs. Predator (2010), F1 2010 and Tom Clancy’s H.A.W.X. 2 whereas Nvidia’s SLI is better in Resident Evil 5, S.T.A.L.K.E.R., Metro 2033: The Last Refuge and Mafia 2. The two technologies have the same scalability in the rest of the games.

We must admit that turning FSAA on doesn't change the overall picture much:

We can only note that each multi-GPU technology improves its scalability, which might be expected since they are both developed for high loads.

The next two pairs of diagrams do not directly pertain to the subject of this review, but should be interesting nonetheless. The first two compare the speed of the single Radeon HD 6970 relative to the single GeForce GTX 570 which serves as a baseline or 0%.

The summary diagrams of this kind make it easy to see in what games a particular graphics card has an advantage. Here, the Radeon HD 6970 is much slower than the GeForce GTX 570 in Tom Clancy's H.A.W.X. 2, Lost Planet 2 and in the high-quality mode of StarCraft 2: Wings of Liberty. There are games where the Radeon HD 6970 is faster, although its advantage is not that large.

And here is how our Radeon HD 6970 CrossFireX tandem compares to the dual-GPU GeForce GTX 570 SLI configuration:

The two GeForce GTX 570s win in Resident Evil 5, S.T.A.L.K.E.R., Borderlands, Tom Clancy's H.A.W.X. 2, Lost Planet 2, and in the high-quality mode of StarCraft 2: Wings of Liberty. In the rest of the games the chances are the same or the Radeon HD 6970 pair goes ahead.

Temperature Tests

Unfortunately, we could not carry out our power measurements tests for technical reasons, but we did measure the temperature of our multi-GPU configurations. To put them under load we launched the test from Aliens vs. Predator (2010) and ran it in five cycles at 2560x1600 with the highest graphics quality settings and 16x anisotropic filtering but without FSAA. It is at such settings that the GPUs reached their highest temperatures.

This test was carried out with the graphics cards installed into a closed system case. Here are photographs of them, followed by their results:

 

 

Quite expectedly, each configuration is very hot. The GPUs of the Radeon HD 6970s were as hot as 94 and 90°C, their fans rotating at 3750 and 2660 RPM (the numbers refer to the top and bottom cards, respectively). The GPUs of the GeForce GTX 570s were 90 and 87°C hot, their fans working at 3270 and 2790 RPM. As the numbers suggest, both configurations are very hot and very noisy. Temperature sensors of different cards and GPUs are calibrated in different ways, but we can say that our GeForce GTX 570 tandem seemed to be less noisy than the Radeon HD 6970 pair. Anyway, we guess the best option for such configurations is a liquid cooling system with full-cover water blocks.

But do the cards differ much in terms of their GPU temperature when they are working alone rather than in a multi-GPU tandem?

 

The single Radeon HD 6970 was as hot as 90°C but its fan was working at 2470 RPM only. The GeForce GTX 570 had a GPU temperature of 87°C and a fan speed of 2610 RPM. So, the temperatures are the same as when the cards work in multi-GPU tandems but the noise level is lower.

Conclusion

As opposed to the midrange graphics cards like Radeon HD 6870 and HD 6850, the top-end single-chip Radeon HD 6970 does not often double the performance when used in a CrossFireX tandem. There seem to be several reasons for that. One is that the speed of a high-performance graphics subsystem depends more on the overall system performance. Then, the Radeon HD 6970 itself is rather a new product, so its driver may not have been optimized properly as yet. Besides, the CrossFireX technology is not supported well by the developers of certain games. But for all these problems, a Radeon HD 6970 tandem can indeed be twice as fast as a single HD 6970, particularly in such games as Crysis, BattleForge, Aliens vs. Predator (2010) and Sid Meier's Civilization IV. We also observed a 100% performance increase in the Unigine Heaven benchmark. The scalability varied from 80 to 90% in some more games as well, which is a very rewarding result. Considering this, we suspect that the potential of CrossFireX with top-end graphics cards is just not yet revealed in its fullness. We hope this technology will be optimized further to deliver a stable and consistent increase in performance across all games (especially in terms of the bottom speed).

Comparing CrossFireX and SLI with respect to top-end graphics cards, we cannot prefer either of them because their standings depend much on a particular game, and we don't think that users will buy a pair of such products for a total of $700-750 to play only a few select games. People who use such solutions naturally expect high performance in every game they launch. As for other aspects, our GeForce GTX 570 SLI tandem produced less noise, had lower GPU temperatures and also came at a lower cost than the Radeon HD 6970 CrossFireX, but you must be aware that replacing the cards' native coolers with something more efficient is not just desirable but vitally important for your multi-GPU configuration to have a long service life and be more or less comfortable to use.