Triple-GPU Scaling: AMD CrossFire Vs. Nvidia SLI

[majithia23]

Two GPUs are great, but are three that much better? When it comes to multi-card scaling, can AMD finally beat Nvidia? Who really needs this much performance? We loaded a super-fast system in single-, dual-, and triple-GPU configurations to find out.

Multi-card scaling usually improves at higher resolutions and details, yet three-way CrossFireX still falls behind CrossFire using a pair of cards. It appears as though this title uses only two of AMD's cards, and that might be a problem with Catalyst Application Profiles. Excellent scaling realized on Nvidia's three-way SLI setup adds insult to AMD's injury.

A third card appears to be about as appealing as an auxiliary nipple at 1680x1050, but higher resolutions prove the viability of both company's three-way solutions. AMD's second card scales a little better than Nvidia's, while Nvidia takes the scaling lead when a trio of boards run side-by-side.

The world looks a whole lot brighter for CrossFireX fans at 2560x1600 and 4x AA, where AMD shreds Nvidia.

Alright Radeon HD 6950s; now you're just showing off.

Mediocre three-way scaling by Nvidia's GeForce GTX 570 is put to bed by supreme scaling in AMD's three-way solution. Results like this make us want to go further, but doing so would require this editor to borrow some extra monitors for Eyefinity.

Two-way CrossFire continues to pull ahead as resolutions are increased, significantly beating SLI at 2560x1600. Three-way CrossFireX looks even better, with three-way SLI becoming inconsistent.

Any Radeon HD 6950 CrossFire solution beats any GeForce GTX 570 SLI configuration at 2560x1600, regardless of whether two or three cards are used. This is probably the only resolution in today's test that really matters, since a single card will pass most tests at anything less. Additionally, 2560x1600 has a similar pixel count as three 1280x1024 displays, so this is "just the beginning" for anyone planning to run in Eyefinity or Surround mode.

Things get ugly for Nvidia at 2560x1600. While a 67% performance gain for two-way and 112% gain for three-way SLI certainly aren't shabby, AMD's 92% two-way and 145% 3-way gains put it in the winner's circle.

This, in spite of the fact that one of our games, Aliens vs. Predator, didn't even benefit from the third AMD card.

Oops! It might be acceptable for Nvidia's better-performing card to consume more power in a single-GPU configuration, but CrossFire's superior performance scaling makes the GeForce GTX 570 a poor efficiency choice in SLI. Note that the power was measured using a game as well as FurMark. This was essential, since the middle Radeon HD 6950 was completely idle during the FurMark test.

The GTX 570s also ran hotter, but this editor would like to note that AMD's sink design leads to extremely tight fan spacing in 3-way mode. Local banshees abandoned our neighborhood at the commencement of power testing.

With Just Cause 2 (at our maximum test settings) making up the most-important portion of our power test, we used the corresponding benchmark values to calculate full-load efficiency. Average performance and power set the full-load baseline, while average power alone (for all six configurations) set the active idle baseline.

Lower power consumption and better performance gave AMD a big efficiency lead, while excellent performance scaling at a constant cost in CPU power allowed multiple HD 6950s to score higher full-load efficiency than a single card.

AMD's Radeon HD 6950 is anything but low-end, and yet its second card provides a huge 92% lead over a single board. Almost as impressively, a third card delivers an impressive 27% lead over two cards at "only" 2560x1600. We could expect even better results at higher resolutions, if only this lab had the monitors for that test. That's why I just expensed two more 2560x1600 displays to support additional testing (just kidding, boss)!

Fears of three-way CrossFireX not being supported by a variety of games were almost put to rest when only a single game, Aliens vs. Predator, didn't realize any scaling improvements when we added a third card. While we still have minor concerns about what other games might suffer similarly (after all, AMD couldn't get F1 2010 working with anti-aliasing until zero-hour for our Radeon HD 6990 review), no performance gain in only one of five tested titles gives us a great deal of confidence in the company's compatibility efforts moving forward. Aliens vs. Predator is the one game where SLI showed its best scaling, a fact that we find odd given that this is not a "TWIMTBP" title.

CrossFire came out with a huge overall scaling lead over SLI, and removing the one title that didn't reflect that average would have made the lead even bigger. Superior scaling allowed two mid-priced Radeon HD 6950s to approximate the performance of two higher-cost GeForce GTX 570s, while three HD 6950s took the performance win over three GTX 570s.

If CrossFire's value-oriented victory in two-way and performance win in three-way configurations weren't enough to convince us, the Radeon HD 6950's lower power certainly did. AMD started out with the highest efficiency at one card, and superb multi-GPU scaling allowed its efficiency to increase with every card we added. When's the last time adding parts made your machine more efficient?

The Test

[T0nyB]

Awesome article, thanks for the share! :) It totally suprised me, that in some tests ATIs best card out there shreded NVIDIAs at 3x SLi. Shame, that Catalyst doesn't take advantage of triple SLi in some cases (or all?).

But to take in consideradion the fact that there aren't many people using triple SLi, that isn't half that bad... If only I had the money to build myself a gaming PC with performance like that... :P

[LeetPirate]

Lower power consumption and better performance gave AMD a big efficiency lead, while excellent performance scaling at a constant cost in CPU power allowed multiple HD 6950s to score higher full-load efficiency than a single card.

I am quite pleased with the efficiency of the Radeon, I think AMD is in the right direction. :)

Wasting energy is for n00bs.