Micro-Stuttering And GPU Scaling In CrossFire And SLI

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thorkle

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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

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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

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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.
 

tmk221

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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

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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

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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

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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 ?
 

Haserath

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Could a frame be analyzed and split into certain pieces for each GPU to process? It would make each frame much more consistent if the load for each GPU was just about equal per frame even if there was overhead for splitting the load up and then having to transfer it to the first cards buffer.
 

SpadeM

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I guess buying 3dfx was the way to go for Nvidia. If all midrange cards are equipped with only one link then I assume that we won't get to see exotic combinations of 3, 4 cards in the next SBM.
 

Samy0806

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Nice article, it was very usefull. BUT why Three-Way, and Quad SLI configurations aren't benchmarked ?
AND i saw that Lucidlogix makes things worse on Radeon HD 6870 X2, what about the Lucidlocix Virtu, integrated in many motherboards, does it affects performance of your graphics card, and if it does how?
 

RazberyBandit

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One reason single-GPU Nvidia boards may trail AMD boards in Mafia II is because Mafia II supports PhysX. With PhysX enabled, a single board can sometimes struggle.

Based on the summary conclusion, does this mean Tom's has firmly gone back to recommending that users purchase "the most powerful single-GPU board you can afford" again?
 
[citation][nom]shoelessinsight[/nom]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.[/citation]

SFR was really good back in the day and it was enjoyable as well stable. Also it scaled well for two way setups but Nvidia killed it off because of quad and tri was becoming popular back in 08. ATI has other rendering modes as well such as tile but they went the afr rout as well. The best days of sli and crossfire are over but one can still try to optimize their way out of some micro shuttering.
 

BrightCandle

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One of the members of XtremeSystems has come up with a program that analyses the amount of variance from the average framerate from a fraps frame time file. Have a look at http://www.xtremesystems.org/forums/showthread.php?258433-Microstutter-in-latest-gen-cards-examples-included&highlight=microstutter for a link and some details on how to use it and results.

Toms could adopt this tool and use it to show the amount of MicroStutter along with their benchmark results. Many other sites like to show minimum fps in their graphs and I think showing the bottom 5% of frame times would be another way to show this problem up and compare the cards in your reviews.
 

greenrider02

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A great article, but of course a few stickler points:
-It's not about Bulldozer
-I would like to read some more detailed observations of problems you were seeing with crashing and driver issues
-A suggestion in the conclusion about what YOU would do with your own setups, as many of us want to know what the pros think
-It's not about Bulldozer
 

jonbla

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So based on the graphs at page 4, crossfire setups will still gain a performance increase but would suffer from minimum framerates similar to a single card?
 

colanusus

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@jonbla
- the line related with a single card is very even (not big fluctuations) that means that the experience is fluid.
- in crossfire you see huge drops of frames and where it happens its not the minimum frame rate which is important but the fact that it related with delays in showing the frames.

To be more explicit: we have 50 frames per second; this is fluid only if they are distributed evenly within 1 second; but if you have 49 frames within 40 milliseconds and than the 50th frame at 1 second you will experience an annoying visual delay
 

colanusus

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@jonbla
- the line related with a single card is very even (not big fluctuations) that means that the experience is fluid.
- in crossfire you see huge drops of frames and where it happens its not the minimum frame rate which is important but the fact that it related with delays in showing the frames.

To be more explicit: we have 50 frames per second; this is fluid only if they are distributed evenly within 1 second; but if you have 49 frames within 40 milliseconds and than the 50th frame at 1 second you will experience an annoying visual delay
 

ojas

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really informative article. this has been my experience with micro-stuttering (if what i'm about to describe is the same thing):

Hardware: Single Geforce 9600GT + CRT monitor @ 1024x768.

Well, first thing that comes to mind is Halo 1. Obviously, it runs smooth as ...well just about anything that's very smooth :p. Point is, while playing sidewinder (empty game, lan hosting) and firing from a ghost, i observed some stuttering while approaching the part where the shade sits (i'm assuming everyone's played halo or seen RvB). I checked the fps graph built into Halo. Turns out that the fps jumps to 120+ from 85 (vsync: on) when i fire. That shouldn't happen (since i have vsync on) but it just does.

Second example is america's army 2. Was playing offline on Border (was testing anti-aliasing and other things). As most of you probably know, AA2 is very CPU intensive and runs mostly on a single thread. I had set the "Maximum pre-rendered frames" option to 5 (default 3) in the nvidia control panel. At 85 fps (vsync), the game was stuttering, couldn't see the fps fall below 80 though, but then again i didn't log it or anything, change in the fps may have been too fast to notice. changed the pre-rendered frames back to 3 and it was fine.

Summary: I wonder if the game code also introduces stuttering? Can the CPU or RAM be any sort of bottleneck?

p.s. Like someone else asked, if a dual card config is producing a min fps of say 100 with micro-stuttering, and if it's capped at 85 or 60 fps (through vsync), will the stuttering remain?
 
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