Nvidia cards of 560 series not compatible in Sli
 

Just a warning for those with Nvidia 560 series graphics cards. The GTX560 and the GTX560 Ti won't work together in Sli mode according to information I have had as reply to my post at Nvidia Sli Club. Because there is a clash in the number of "CUDA CORES" with the two cards.

GTX560 = 336 CC
GTX560 Ti = 384 CC.

So those of us who are running GTX560 cards and want to go SLI be careful as to what you buy as the second card.

EVERYONE willing to buy a SLI / CFX solution, or, as a matter of fact, any ATI videocard, please read this article.

Why, really what do it change?
Just because you can measure something it don't mean everyone can see it.
I couldn't use IPS panels because I seen ghosting in certain types of games, lots of people can't see it but funny thing is I rarely notice micro shutter.
The main thing I got out reading that is if you game at ultra high resolutions (2560x1600) you need more then a 1GB video card, I maybe wrong but I do no every hardware review site will be looking at this and soon have an opinion.

Because that article is a perfect explanation for the micro-stutters everyone is complaining in here.

And because after reading that article, you won't ever consider getting a SLI/CFX solution for IL2 CoD.

Perfect. That's the reason why i noticed best performance after "Steam Ghost Patch" and lost some in the new beta patch. Max-Min-Average FPS in CloD and other modern Combat Sims "microstutter" fest means nothing.

I also get that shutter in COD with one card.

I had seen this linked before but only just now took the time to read it. Just...wow. Multi-hundred dollar GPU setups that companies know face such a problem and they don't bother telling customers about it, and we're sitting here complaining about a $50 game :-P

On a serious note, the summary for those who don't want to read the entire article.

1. As long as the average FPS is in an acceptable range, maintaining the illusion of movement in a game depends more on having subsequent frames render in a similar amount of time each, and less on the absolute FPS numbers. FPS can't measure this because it averages the results over an entire second, so they use a new unit to measure it: milliseconds needed per frame rendered, so if this catches on in further reviews expect it to get an acronym of its own like mspf or something :-P
   
2. Stutters are perceptible "breaks" in this illusion, caused by having subsequent frames render in amounts of time that differ more than a certain threshold: if mspf between subsequent frames differs more than a certain value, stutters occur.
   
3. Dual GPU setups are essentially a master-slave arrangement. While both GPUs render an equal part of the picture if AFR is used (alternate frame rendering, GPU1 renders frame 1, GPU 2 renders frame 2, etc), only GPU1 is connected to the monitor: GPU2 has to push the data "through" GPU1 before it reaches the monitor and this raises the mspf for GPU2. Every second frame takes longer to render than the previous one.
   In other words, dual GPU setups have an built-in "stutter generator" by hardware design, it's just that we don't always perceive it because it doesn't always go above that certain threshold.
   
4. Fraps (and maybe other FPS measuring tools too?) is inaccurate in measuring this, because it measures FPS by looking at when the frame is passed on to DirectX, not when it's actually rendered and displayed, so it misses that loop which institutes the delay.
   And now for the points that are especially relevant to CoD and flight sims in general...
   
5. A high vRAM usage exacerbates this problem.
   
6. The problem is more prone to occur on game engines that track time more accurately.

We know CoD's textures are quite large in size (high vRAM usage) and we know all sims are very time-sensitive. Tracking the ballistics of weapons down to individual bullets/cannon rounds in relation to the target, especially in an age where hitboxes are no longer used, means a high demand for precision in how time is measured: the game engine has to "slice down" the time in smaller pieces and the finer control over time the engine has, the more pronounced the problem becomes.
But we absolutely need that time control for accurate ballistics, FM and DM, not to mention consistency in multiplayer combat.

Ironically enough, nVidia's solution to this is to lower overall FPS by inserting a metering system in SLI setups that will delay frames that are rendered faster than others to produce a more even sequence (since they can't speed up the slow ones), which is something people who've been flying the microsoft civilian flight sims have been doing for a long time, either by setting the in-game FPS limiter or by using external ones.

It also explains perfectly well why my FPS with the latest beta are lower but the game is looking smoother.

In conclusion:

• FPS measurements on their own don't mean much, as stutters can occur even on high FPS. Plus, FPS are measured inaccurately by taking measurements from inside the rendering loop instead of measuring the entire cycle once it's completed: the point where the problem occurs is further down the "pipeline" than the point our FPS measuring tools get their data from, so they miss it completely.
  
• The things a flight sim needs to do demand a certain design of the foundation game engine that is more susceptible to these effects.
  
• Lowering the graphics load and especially reducing vRAM usage makes the problem harder to spot because the difference in mspf between individual frames is lowered (which, as far as CoD is concerned, means turn your texture size down a notch).
  
• It's an innate hardware design issue first and foremost and impossible to optimize 100% for every single game.

So, unless you're running quad SLI/Xfire on 100FPS with a sufficiently low and steady mspf between subsequent individual frames, sell your multi-GPU setups and put that money on a beefy single GPU - single card setup, it will run better and get you some money back too that you can spend on another upgrade ;)

Interesting reading, thank you for the education :)

Seriously?
I have hundreds of games that all run smooth....except for this one and now its hardware because one hardware review site writes an article.
People with the fastest GPU's on the market get shudder in this game and it happens with one card.

Same here. I also get stuttering when I run just a single card.

This is the only game with these massive stutters for me. It WAS this and Rise Of Flight, but guess what...after their latest patch, they fixed all their remaining SLI problems. This is after nearly a year of 777 Studios blaming nVidia for not having the right profile to support their game. I'm sure it had to do with a combination of both parties, but still...after THEIR patch, it worked. Hmmm...

I refuse the argument that it's the fault of multiple GPUs and not the programmer. If that was the case, all my games running in SLI would experience problems. But, conversely, games of all genre (ArmA2, RoF, Crysis 2, Metro 2033, ANYTHING) run nearly twice as better in SLI as they do just using one card. And no stuttering whatsoever.

ArmA2 and RoF both have plenty of calculations going on. Even if you made the argument that CLoD has more, it still shouldn't result in the nearly unplayable jitters I personally experience in-game.

And hey, I'm patient. I'll wait. As long as there's a patch that comes, I'll wait. The only way I'd be legitimately choked is if the devs simply washed their hands and said, like some of you, "you just shouldn't have got an SLI setup because they don't work." Sorry. That's just not true.

I agree with Mr Greezy, that the micro stutters we are getting aren't happening in other games that have been optimised. Call of Duty 4, for e.g. which is DX9 runs smoothly with Sli. I thought it might have been related to DX but unless it only affects DX10 then that isn't the problem. I also have no problems with ROF (DX10) after the last patch which has with the help of Nvidia runs smoothly with no break up of graphics. All the earlier Il2 series have no problems either (Ok Il2 is OGL ) so the problem points to optimisation of COD. Some of us have Sli running OK but not perfect, lets be patient and give the team our support with positive vibes and let them get on with it.

Guys please read my previous post again, as you seem to be reading into it more than it states. I didn't say "sit tight and do nothing devs, these guys were asking for it for buying dual GPUs", far from it. That's a totally different interpretation and it's not mine.

So, to recap, i'm not saying CoD is beyond optimizing or that everything is perfect, i'm just saying it has been said for ages that dual-GPU setups have an inherent hardware disadvantage by design that causes stutters in some games and now someone took the time to measure it accurately, confirm it via AMD/nVidia representatives and present it for the rest of us. Actually, if the article is accurate then it causes stutters in most games, but the "gap" is not always perceptible by the human eye and so it doesn't bother us most of the time.

In that sense yes, seriously, there's a hardware design issue in dual GPU setups overall (and in some single GPU setups too), which shows even more in CoD due to certain engine restrictions and bugs.

Sorry my man. Didn't mean to sound heated. I'm just speaking as a non-ultra technical PC user. As far as I'm concerned, everything else works great except CLoD. So I'm a fan of SLI.

It was a good article to read because it shows what the game devs have to deal with when working with Nvidia/AMD to get SLI/Xfire working well. Nuthin' ever comes easy, it seems!

Not true. Single GPU runs it smooth if you reduce settings to match your card performance (texture quality and lighting/shading mostly). I can confirm this for 2GB single GPUs at least.

I tested a EVGA GTX 580 3GB last night and even bumped my overclock to 4.6 and it shuttered in the same places I normally see it.