Micro-Stuttering And GPU Scaling In CrossFire And SLI

Test System And Benchmark Selection


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Test System
CPUIntel Core i5-2500K @ 5 GHz to verify GPU scaling
CoolingProlimatech SuperMega + Noiseblocker Multiframe PWM
MainboardGigabyte Z68X-UD7

RAM8 GB Kingston HyperX 1600 "Genesis"

System SSD256 GB Samsung 470 SeriesPower SupplyCougar GX 105080 PLUS GoldTotal1050 W

Combined Power 3.3V/5V160 WCombined Power 12V1008 WEfficiency93 %OSWindows 7 x64 UltimateTest EquipmentCurrent and Power Meter

Energy Logger 4000 (Conrad Electronic)• long-term measurements• monitoring• power measurements up to 1.2 KWVoltcraft

SBC-500 (Conrad Electronic)• precise measurements down to the milliwatt range• power measurements up to 500 wattsSound Level Meter

Voltcraft SL-400 (Conrad Electronic)• sound level measurements• long-term recording• monitoring

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Syntethic Benchmarks
3DMark 11Grahpics Tests 1-4
Unigine Sanctuary v.2.4Dynamic lightsHDR renderingParallax occlusion mappingAmbient occlusion mappingTranslucenceVolumetric light and fogParticle systemsPostprocessingInteractive experience with fly-through mode
Gaming Benchmarks
DirectX 11Metro 2033Aliens Vs. Predator
DirectX 10Call of JuarezS.T.A.L.K.E.R.: Call of Pripyat
DirectX 9Mafia II

Performance Categories: Gamer and Enthusiast

Although we cover a wide range of settings and resolutions in our launch coverage of various products, and will continue to do so, this piece includes two more generally-applicable performance categories that also take the acquisition cost into consideration. Our Gamer category is tested at 1680x1050, and our Enthusiast category is benchmarked at 1920x1080. We also base the image quality settings on both classifications.

Performance Index and Calculation Method

Instead of using cumulative frame rates to rank a graphics card, this review ranks cards in those same Gamer and Enthusiast classes. A graphics card that may be ranked rather low in the Enthusiast column might be completely usable in the Gamer category. Cumulative frame rates do not shed light on performance under specific conditions. Thus, we're replacing that old system with more transparent rankings.

So, how do we obtain these values? We take one representative from each GPU manufacturer, both for mid-range cards (AMD Radeon HD 6870 and Nvidia GeForce GTX 560 Ti) and high-end cards (AMD Radeon HD 6970, Nvidia GeForce GTX 570), and assess their behavior in 15 games. Then, we compute an average for each of the two card groups, creating two fictional 'Raforce Gedeon' cards. We use these two models as a reference for quality settings in each benchmark test and dub these synthetic frame rates the 100% level for the Gamer and Enthusiast categories, respectively, for each benchmark. The sum of all performance percentages, divided by the number of tests, yields two indexes. As the 'Raforce Gedeon' card is manufacturer-agnostic, advantages held by specific cards are eliminated from the get-go. This might sound complicated, but it really isn't. So long as you test using typical game settings, the rankings are a good indication of the price/performance ratio for each graphics card.

Power Draw and Temperature Measurement

We fully-loaded our CPU with Prime95 running threads at low priority in the background. Then, we measured the power draw of an entry-level graphics card with well-known power characteristics (first at idle, and then with FurMark running). Subtracting the card’s idle and load power from the total system power yielded, in each case, the total system power draw without a graphics card. These two values nearly matched, which allowed us to simply subtract 131 watts from all subsequent power measurements in order to obtain the power draw of the graphics card by itself. Of course, we also analyze the total power draw as a sanity check.

  • thorkle
    This is a very interesting article, I have wondered about this issue myself many times in the past. I was always curious why I would see strange lag like anomalies while still achieving perfect frame rate. Bravo Toms
  • compton
    Well, I'm a little surprised that three cards in Crossfire seem to eliminate visible microstuttering -- I would have guessed that triple cards would increase stuttering. But it also seems like there must be other factors at work. Unfortunately, there really isn't a good way to test for other factor -- if you even could know what to test for. In some circumstances, it seems like my monitor is causing some issues. If I play a game (lets use Fallout New Vegas for example) at a Synced 60FPS, you can look at FPS and it never deviates. It only uses 1/3 of my GPU cycles. But on one monitor, at the same resolution, it micro stutters. On another monitor, it looks perfectly fine. I thought it was some lag variance -- but then I've been told lag is always constant, that the reason lag varies in monitor testing is improper test methods. What ever the reason, it's actually really annoying. And I'm not anything approaching a competitive FPS player. Thanks for helping to track this issue down.

  • iam2thecrowe
    so will you now change your best gpu for the money from 2 x 6850's, since they obviously suck. I already bought one 6850 thinking it would be great to crossfire later and that was the best choice according to you toms........now i will have to throw it in the bin come upgrade time and buy a better single card. Oh, and AMD/Nvidia, if you cant get dual card configs to work properly, don't offer them, your wasting our money. Please fix this microstuttering crap, im sure it would be possible with a driver tweak.
  • 1kbuild
    What happens with Vsync turned on?
  • pirateboy
    why wasn't hybrid crossfire mentioned in this article?
  • bombat1994
    i think the MSI Radeon 6870 Hawk is the best graphics card on the market right now in terms of heat, power, performance and price
  • tmk221
    in most games you can limit maximum frame rates. So maybe if you limit max FR to let say 10 to 15 above min FR then the Micro-Stuttering effect would be gone ? anyone tried this? please share
  • shoelessinsight
    What is performance like using other load-balancing methods, like the split frame rendering that SLI originally used, or ATI's Scissor mode? Are these modes still available to those that choose them?

    Obviously, they won't reach frame rates as high as those attained through AFR, but if the frame rate loss is small enough, those modes might still be justifiable if they eliminate micro-stuttering altogether.

    I'd be curious if these alternate methods could justify the cost of an additional card through added performance without coming with the drawback of micro-stuttering.
  • boletus
    Regarding the decreased stuttering with 3 or 4 cards: could this be a similar effect to superimposing sine waves? Two waves a half cycle apart show visible peaks and valleys, while three waves at evenly staggered cycles form a much smoother band (on a graph or a scope).
  • haplo602
    I ma confused ... you are using 2 identical cards, so the frame rendering times as show on the metro 2033 second would be THE SAME on a single card as on a dual card configuration. the only difference is when each card starts to render right ?