PCGH: Micro stuttering on multi GPU solutions

[cadaveca]

Yes, problem is evident in dualcard configs in XP or Vista, 32-bit or 64bit, Vista shows same problems with 3-4 cards as well.

[KoHaN69]

What about SLi and CrossFire on linux?

[cadaveca]

rofl. Are you serious? PLease tell me you are not. I can't see why you are asking this question....there is no Linux Crossfire driver.

[KoHaN69]

I'm not sure about crossfire, but there's definitely an SLi driver for Linux.
Please refrain from being patronizing.

[cadaveca]

Sry, man. I humbly apologize. there's just no games for linux..most are windows, so the need for Crossfire on linux is very small.


I DIDN't know there was SLi for linux...I'm actually quite surprised. I wonder why they've invested time in that?

[KoHaN69]

nvidia always supported linux
ATI's linux newer drivers are open sourced, so crossfire might turn out eventually.
linux has official ports: Doom3, serious sam, UT2k4, Enemy Territory: Quake Wars,
and Unreal3 is coming soon

+wine and cedega of course

it's not DEAD

[cadaveca]

no, but I've never had Linux in my mind as an option for graphics rendering...power computing. Guess maybe I'll have re-evaluate that!

[Bo_Fox]

Wow!!!!! That explains all of the constant stuttering problems I experience with my games when using my 7900GTX-SLI PC instead of my other 8800GTX PC.

My favorite racing game, Test Drive Unlimited, is unplayable on 7900GTX SLI, although it can run at 35 fps sustained. The constant stuttering just does not look good at all, and looks more like 15 or 20 fps. Many other newer games also stutter more than on my 8800GTX.

[FischOderAal]

i can confirm that on 16x/4x the stuttering gets much worse, while it is there i only get one barely noticeable stutter in 5 minutes on the X16/x16

makes sense to me. on P35 x4 is connected via the southbridge to the northbridge and therefore has a higher latency.

[saaya]

if you get a stutter ever 5 minutes, then thats NOT caused by the dual videocards. micro stutering is constant, what you experience is caused by your system memory beeing full and the game has to read/write data from/to the hdd

[Dirtbiker14519]

Just wanted to Bump this and let everyone know that the new 8.4 drivers didn't resolve this issue . I guess I'll put them on ebay and buy an nVidia card.

[fireice2]

single GPU FTW!

[Dirtbiker14519]

Yep. School of hard knocks i guess :\.

[KoHaN69]

Yeah, I've always preferred single card too.
if you're gamign @ 1600x1200 or higher (which you should be, anything lower and a single midrange card should be fine for you) sell the GTX and get a 8800GTS 1gb or wait for 9800GT 1gb

[GoldenTiger]

Has this been fixed ever on the nVidia side, or still a constant issue?

[Bo_Fox]

Funny thing is when I force split-frame rendering, it seems to help a bit with the "micro" stuttering. However, SFR does not work for some games and I have to suffer severe micro-stuttering (and additional lag) with AFR mode in Test Drive Unlimited, UT3 and Bioshock, COD4, Transformers, ETQW, and most of the newer games.
So I use my 8800GTX for those (except for ETQW).

[saaya]

sure, sfr should improve the situation a lot, stuttering should only appear when one of the gpus needs more time for its part of the frame than originally planned. if sli is perfectionized then sfr or atis tile mode should cause no micro stuttering at all.

[adamsleath]

wot a kick in the arse for multicards :|

does running cards at exact same clocks help? does it only happen in some games? just curious as ive never run crossfire.

it would be helpful to have a list of games for 2, 3 and 4 card/gpu setups which work with absolutely no problems. it looks like a can of worms to me.

[Seraphiel]

Is there a game, where it is certain this phenomenon can be observed with nVIDIA SLI?

Some SLI supported games mentioned I have played personally, with and without SLI, and there is no doubt to me, that all of them felt more smoothly with SLI than without.

frame time looks a bit like this:

1:00:01 frame 1
1:00:04 frame 2
1:00:31 frame 3
1:00:34 frame 4

Please explain how that would ever give a less smooth experience than:

1:00:01 frame 1
...
1:00:31 frame 2
...

I really don't understand it, so please (someone) explain it to me. If the above is the correct explanation, then worst case scenario would be the same as without SLI, right?

I don't think the above explanation is the correct one, or at least not the complete one.

[AliG]

Hopefully the r700 won't have this issue by sharing the memory bus

[onewingedangel]

Please explain how that would ever give a less smooth experience

When there an even gap between frames your mind tend to fill in the blanks, so as long as your getting sufficient frame rates it appears smooth. With uneven gaps between frames you become aware of the uneven motion even if your getting more frames than required for what we would consider smooth motion.

30fps with even gaps can appear smooth, wheras the uneven gaps are noticable even with very high frame rates. This can mean that playing a game with a single card at 30fps could appear smoother than playing a game in sli at 60+fps.

[saaya]

wot a kick in the arse for multicards :|

does running cards at exact same clocks help? does it only happen in some games? just curious as ive never run crossfire.

it would be helpful to have a list of games for 2, 3 and 4 card/gpu setups which work with absolutely no problems. it looks like a can of worms to me.

it affects sli AND xfire, it happens in ALL games...
its just more apparent in some games compared to others...

Please explain how that would ever give a less smooth experience than:

1:00:01 frame 1
...
1:00:31 frame 2
...

I really don't understand it, so please (someone) explain it to me. If the above is the correct explanation, then worst case scenario would be the same as without SLI, right?

I don't think the above explanation is the correct one, or at least not the complete one.

i already explained it 2 times, did you read the entire thread? :P

ok... here we go again
if you draw a cartoon you need a certain amount of pics per second to show to make it look fluent, right? well you can make things look more fluent by doubling the frames. you just show each frame twice, that actually does look more fluent even though you dont get more information.

BUT, this only works if you insert the frames propperly and show them exactly between the other frames. what happens with sli and xifre now is that the extra frames that the second or third/fourth gpu adds, are not displayed or rendered in their propper time windows.

its a bit difficitcult to understand, i admit that...
its basically a bad syncing of game time and frame time.
essentially the stuttering is caused by the game time not matching the frame time, so when we actually see the frames, they dont show a constant flow of time between the different frames, but it stutters.

a movement isnt steady but from one frame to the other the game appears to run slightly faster, then slightly slower. it happens so fast that we perceive it as stuttering.

Hopefully the r700 won't have this issue by sharing the memory bus

i dont know... i dont think you need new hardware to get it to run propperly...
its possible with topdays cards to adjust the frame times, but... it means less performance.
maybe with new gpus they find a way to do adjust frame times without a perfomance impact... hopefully!

[fireice2]

Does this also happen with the GX2's and X2's?

[Seraphiel]

When there an even gap between frames your mind tend to fill in the blanks, so as long as your getting sufficient frame rates it appears smooth. With uneven gaps between frames you become aware of the uneven motion even if your getting more frames than required for what we would consider smooth motion.

30fps with even gaps can appear smooth, wheras the uneven gaps are noticable even with very high frame rates. This can mean that playing a game with a single card at 30fps could appear smoother than playing a game in sli at 60+fps.

Well, in Saaya's example the delay was constant (0.00.03), but even if it wasn't so, I am not sure that it would give a less smooth experience. Also, framerates can be pretty inconsistent when playing a game. I wish there was an easy way to actually test the theory.

its a bit difficitcult to understand, i admit that...
its basically a bad syncing of game time and frame time.
essentially the stuttering is caused by the game time not matching the frame time, so when we actually see the frames, they dont show a constant flow of time between the different frames, but it stutters.

a movement isnt steady but from one frame to the other the game appears to run slightly faster, then slightly slower. it happens so fast that we perceive it as stuttering.

That actually makes sense to me, if it means that the frames observed are not in sync with what they "should be" (1.00.01 frame are shown at 1.00.01, but frame 1.00.04 are shown at 1.00.06, frame 1.00.07 are shown at 1.00.07, but frame 1.00.10 are shown at 1.00.12 etc.) ?

And if they were in sync, even if irregular/inconsistent, then it would still be more smooth if more frames were rendered, right ?

Yes, I did read all of the thread. Could be me that just don't get it

Still, I personally haven't experienced this with SLI, so perhaps it is OS/driver/game etc. related and not a general problem. Wouldn't it be a problem in all games for all CF/SLI users, if that wasn't the case?

[onewingedangel]

Well, in Saaya's example the delay was constant (0.00.03)

No it wasn't, look again.

1:00:01 frame 1
0:00:03 gap
1:00:04 frame 2
0:00:27 gap
1:00:31 frame 3
0:00:03 gap
1:00:34 frame 4

Also, framerates can be pretty inconsistent when playing a game.

Using a single GPU when at 30fps theres a specific gap between frames (1/30 second), and when at 70fps whilst the gap is different (1/70 second), its still a consistant rate between frames. When you transition between frame counts you notice this as speed up or speed down, but either way it is still smooth as the gap between frames is consistant with the ammount of frames rendered.

With the AFR multi gpu approach the timing between frames can be inconsistant hence appearing as stuttering. Look at the example below:

EG. Single GPU
FRAME1 >30ms> FRAME2 >30ms> FRAME3 >30ms> FRAME4

EG.AFR
FRAME1 >10ms> FRAME2>20ms>FRAME3>10ms>FRAME4>20ms>FRAME5>10ms>FRAME6>20ms>FRAME7

Even though your getting additional frames from the second GPU its the timing of those frames that causes the stuttering. Under ideal circumstances the gap between the frames should be consistant at 15ms.

Add into that that the speed up and slow down experienced when the fps changes isn't neccesarily consistant between the to GPU's and the gap between the frames can be thrown out by an inconsistant rate, which further complicates things.