My thoughts on the whole SLI verses Crossfire.

[ChrisRay]

Well. This is just some speculation, ((Xfire,)) Some facts ((SLI)) and some just generic thoughts from me. I decided to wait a while to get a little more information about it. But here are my thoughts.

The biggest issue being brought up right now is compatibility. People have said that they dont like Nvidia's Profile system because it just doesnt work. While I can understand the criticism. There's usually good reason for this. If a game isnt seeing any performance benefit. Why even enable the second card? It'll just produce more heat. Draw more power. And can sometimes bet detrimental to performance by 1 or 2% at best. The Profile system is somewhat moot anyway. Anyone who'd buy a such setup would obviously know how to install coolbits. And by that point. The Nvidia SLI setup is pretty flexible in your control over SLI applications and how the driver reacts to SLI. There's really no reason why SLI users wouldnt want to do this anyway.

CPU limited scenerios wont benefit anyway. So may as well turn it off. I see no reason to believe ATI will make CPU limited scenerios faster either. I mean just take a look at this TweakTown article (http://www.tweaktown.com/document.php?dType=article&dId=773 ) where it shows that ATI pretty much experiences the same issues Nvidia SLI does in CPU limited scenerios. So I'm failing to see how this is much different from SLI in that regard. Not even ATI is gaurenteeing speedups. So in regards to application support.

In all honestly. ATI is using profiles too for its AFR multirendering aproach. If you look closely between the lines. I doubt anyone will disagree that AFR is right now the best aproach to scaling GPUS and ATI is certainly going to target all the same big name games Nvidia has. If that doesnt work. Go to Super Tiling for Direct3d and Scissors for OpenGL. While Nvidia will default to SFR if AFR doesnt work. Or single GPU rendering if performance isnt any better. IMO this once again exactly the same thing that SLI is doing. The only real difference is. Nvidia allows you to control the profile system with coolbits.

Another thing I've been thinking of. Regarding Control of the multi GPU setup. Currently with coolbits or a few application utilities such as Nhancer. You are allowed complete control over the profile system. You can select AFR, SFR, AFR2 (For RTT type apps)) or single GPU rendering. I've grown really fond of this system honestly. At first it seemed a bit a bit annoying to have to manage this. But now that I have managed it. I can really appreciate its uses. You can decide if you prefer AFR or SFR, without having to wait for driver updates at all. And if you can get away with AFR. There's very little reason not to use it providing it has no compatibility tweaks. Because it will scale geometry as well. Both SFR and Super Tiling will not scale Geometry so the ability to control this is a nice feature. I am not sure at this point if Xfire will allow control over this. As it stands now and from understanding of press released. The Catalyst AI controls whether AFR is used and Scissors/Tiling are used instead. Hopefully it will later allow for the flexibility of Nvidias profile aproach. My guess is ATI will allow for this flexibility as well.

Regarding Super Tiling. I dont know a whole lot about this mode other than what I have read and I have no idea how it scales in real world.. I do know it suffers all the same issues that SFR, and AFR suffer when it comes to render to texture scenerios and other areas where SLI has been known to fail. The only other thing is it doesnt work in in OpenGL. It also doesnt scale Geometry much like SFR.

Scissors verses SFR is also an interesting comparison. Unlike SFR which will dynamically adjust the GPU load for optimal performance. Scissors will just set the split and that is that. SFR has the potential to be more optimal under GPU load situations than scissors. I'm not entirely sure how scissors will manage the split frame aproach but I believe it can be set dependent on the app as well. It also can be split vertically or Horizontal. But from what I have read the horizontal aproach is more ideal in most situations. The argument against the load balancing of SFR is that it produces some CPU overhead. The argument for load balancing is under GPU limited pixel bound scenarios it has greater potential. I think its important to note the strength and weaknesses of each setup.

The last and not least is SuperAA. Very neat concept. I like it. Actually. My only problem with it is. Its not compatible with scissors, afr, or tiling. It cant be used with any performance enhancing mode. Which makes me somewhat question its viability. I really dont see the difference between using this mode or increasing resolution/anti aliasing settings with a performance SLI/Crossfire mode. Perhaps time will better tell. Once I see some performance comparisons with it. It'd be much better to judge its viability.

Ahh well. Sorry for the long post. Just trying to organize my thoughts on what IMO the important issues regarding the new competition and multi GPU rendering. I'm not trying to take anything away from ATI here and I am honestly happy they have a multi gpu platform now. What bugs me is some of needless fud when the two adaptions have alot of the same limitations/strengths.

[skoprowski]

Look at the new article in Tom's hardware- ATI is using profiles just like Nvidia.

"Catalyst A.I. fixes which games run in which rendering modes. If the driver does not recognize the game, the standard mode (SuperTiling) for Direct3D and Scissor for OpenGL applications is selected automatically. Users can only choose SuperAA mode freely."

I'm pretty sure I just read a recent interview with the guy in charge of SLI at Nvidia and he said that Nvidia's hardware is capable if supertiling too. All in all I think Crossfire and SLI is comparable. I am willing to bet we will see driver changes soon from Nvidia.

[Cota]

Supertiling has been used by Evans & Sutherland for simulation systems since the radeon 9700 days.

its supposed to have huge performance increase. what's puzzling is that Xfire version only works in d3d when the natural thing would be that it worked with openGL.

Vertical splitting is not possible simply because you of the way CRT handles video signals (at least on nvidia's SLI). It should be possible to implement it for digital displays via DVI.

I find it funny that over and over people get exited with marketing instead of real world performance.

Of course ATI is going to say Xfire is the next best thing since sliced bread, I have a hard time believing that their implementation will be fully compatible with all games (which doesn't mean it will increase performance in all of them).

[skoprowski]

So why doesn't this pertain to ATI? This seems like a logical explaination as to why Nvidia is not using supertiling. I don't see this changing for ATI. I really think the ATI PR machine is blowing a lot of smoke.

http://www.penstarsys.com/editor/tech/graphics/nvidia/sli_inter/

Can you quickly take us over the advantages and disadvantages of SLI as compared to a supertiling solution?

"NVIDIA has been working on SLI technology for many years. In fact, NVIDIA has been designing scalability logic into their GPUs since GeForce 3. However, an effective multi-GPU technology is non-trivial, requiring extensive research & development in both hardware and software. NVIDIA designed SLI technology with the flexibility to support multiple rendering algorithms, offering optimal performance for different types of applications. Our two primary algorithms are dynamic split frame rendering (SFR) and alternate frame rendering (AFR), but there are others.

Supertiling is another algorithm that may be used to scale performance. The problem with supertiling is that it isn’t able to scale geometry like AFR can. Supertiling also has a problem with over-fetching textures (as did scanline interleaving) because of the number of textures that cross the tiling boundaries. This means that each GPU would have to fetch the same texture for neighboring tiles. In SFR, we have one edge where textures can cross boundries. In supertiling, you have many, many more edges and the problem is multiplied linearly with the number of edges. These double-fetched textures can eat up valuable bandwidth.

When developing SLI technology a number of different algorithm options were investigated. In fact NVIDIA looked at supporting supertiling as well, however it simply wasn’t the optimal choice for delivering the highest scaling performance. "

[Cota]

"NVIDIA has been working on SLI technology for many years. In fact, NVIDIA has been designing scalability logic into their GPUs since GeForce 3. "

I don't believe that, nvidia hasn't been able to deliver multichip technology to quantum3d for years. Quantum3d still has simulation systems based on 3DFX!!!!! (up to 16 VS-100) and just recently incorporated dual chip (nv4x) and sli based simulators.

[jAkUp]

hmmm... I didn't see this posted anywhere:

http://www.tweaktown.com/document.php?dType=article&dId=773

X850XT Crossfire

Normal
1024x768 – 85.4
1280x1024 – 83.1

4xAA 8xAF
1024x768 – 69.6
1280x1024 – 52.2

GeForce 6800 Ultra SLI

Normal
1024x768 – 83.8
1280x1024 – 82.5

4xAA 8xAF
1024x768 – 67.8
1280x1024 – 53.4

[spanker]

The last and not least is SuperAA. Very neat concept. I like it. Actually. My only problem with it is. Its not compatible with scissors, afr, or tiling. It cant be used with any performance enhancing mode. Which makes me somewhat question its viability. I really dont see the difference between using this mode or increasing resolution/anti aliasing settings with a performance SLI/Crossfire mode. Perhaps time will better tell. Once I see some performance comparisons with it. It'd be much better to judge its viability.


since some games simply dont work with any of the rendering mode's, you dont have to let one of the cards sit idle doing nothing, you can atleast use it to bump up the AA, from 4x to 8x for almost no fps hit

[ChrisRay]

since some games simply dont work with any of the rendering mode's, you dont have to let one of the cards sit idle doing nothing, you can atleast use it to bump up the AA, from 4x to 8x for almost no fps hit


Wait a minute. ATI has alluded that super tiling works in every Direct3d application. In reality this is the same as SFR. But it doesnt improve performance always. We havent seen any benches on the new super AA modes to assume they have no performance hit. This is something people need to understand. SFR has extremely high compatibility too. It just cant bring performance up in every scenerio. In many cases when you're CPU limited like this. You can turn on 8xAA and it'll play like its 4xAA. Again. How is this different?

Supertiling has been used by Evans & Sutherland for simulation systems since the radeon 9700 days.

its supposed to have huge performance increase. what's puzzling is that Xfire version only works in d3d when the natural thing would be that it worked with openGL.


It may very well have huge performance increases. But my guesses it's going to be very similar to SFR. Since both modes can do nothing to scale geometry.

[SH64]

hmmm... I didn't see this posted anywhere:

http://www.tweaktown.com/document.php?dType=article&dId=773

http://www.nvnews.net/vbulletin/showpost.php?p=621418&postcount=102

you didnt search very well :p

The last and not least is SuperAA. Very neat concept. I like it. Actually. My only problem with it is. Its not compatible with scissors, afr, or tiling. It cant be used with any performance enhancing mode. Which makes me somewhat question its viability. I really dont see the difference between using this mode or increasing resolution/anti aliasing settings with a performance SLI/Crossfire mode. Perhaps time will better tell. Once I see some performance comparisons with it. It'd be much better to judge its viability.

Hmm thats news to me .. so 10x/12x/14x cannot be used with a game running in any of CF's 3 rendering modes ??
if thats the case then those modes will turn out to be just like nVIDIA's 8x/12x/16x support with the expection of the less performance hit which will still be large in single GPU mode.
as you said though we need to see some performance numbers to judge.

other disadvatage of ATi's CF (vs nVIDIA's SLI) might be that user wont be able to use dual custom cooled video cards because ATi only has the right to provide the master cards AFAIK & those will use ATi standard cooling only.
its a little disadvantage though because people might get aftermarket coolers instead if they had cooling issues or overclcoking plans.


one of the things i liked in ATi's CF is the ability to switch between single GPU & CF mode without the need to reboot. SLI still requires rebooting. yes thats a minor thing but i like it!

[Beng]

The last and not least is SuperAA. Very neat concept. I like it. Actually. My only problem with it is. Its not compatible with scissors, afr, or tiling. It cant be used with any performance enhancing mode. Which makes me somewhat question its viability. I really dont see the difference between using this mode or increasing resolution/anti aliasing settings with a performance SLI/Crossfire mode.

In games where one X850XTPE (or future R520) is powerfull enough to play it @ max settings (=1600x1200/6xAA/16xAF) you can use the second card's power for a higher AA level without performance penalty. (not only higher AA, AF can increase too from 16 to 32 x AF).
And plenty of people use 17 or 19 inch LCD's, their maximum res is 1280x1024. In most games they hardly need the extra power from the second card, so they can use it as a AA enhancer.

[ChrisRay]

In games where one X850XTPE (or future R520) is powerfull enough to play it @ max settings (=1600x1200/6xAA/16xAF) you can use the second card's power for a higher AA level without performance penalty. (not only higher AA, AF can increase too from 16 to 32 x AF).
And plenty of people use 17 or 19 inch LCD's, their maximum res is 1280x1024. In most games they hardly need the extra power from the second card, so they can use it as a AA enhancer.


Like I said. How is this any different than Nvidia users enabling 8xS on games where one card is powerful enough to use 4xAA/8xAF at 1600x1200 with AFR/SFR enabled? Its a good idea. But in many applications where the CPU the bottleneck. You can do this with SLI too. I dont see the dramatic difference here. The same argument can be used for Nvidia hardware with 8xAA and even 12x modes. Providing the framebuffer will allow it anyway.

[Kojiro]

lol don't you see, SLI and Crossfire are evil plots devised by nvidia and ATI to make uber dork buy the same card twice. It just that ATI was playing it safe and waited if SLI would catch on. Now that it has, ATI want's to cash in on it too in a slightly modified SLI settup. (Advertized as improvements, though really subtle differences that bypasses patent laws. Nvidia can sue if it were too similar.)

ATI and Nvida = "Now that we sold our cards to our fanboys twice for double the performance, we will release a new single card with 4 x the power of the last king of the hill card."

[retsam]

lol don't you see, SLI and Crossfire are evil plots devised by nvidia and ATI to make uber dork buy the same card twice. It just that ATI was playing it safe and waited if SLI would catch on. Now that it has, ATI want's to cash in on it too in a slightly modified SLI settup. (Advertized as improvements, though really subtle differences that bypasses patent laws. Nvidia can sue if it were too similar.)

ATI and Nvida = "Now that we sold our cards to our fanboys twice for double the performance, we will release a new single card with 4 x the power of the last king of the hill card.


after reading this my I.Q went down 20 points ....

[SH64]

after reading this my I.Q went down 20 points ....

Really ? i lost 30 :(

[Remij]

some good points here.

[retsam]

Really ? i lost 30 thats becouse you have more to loose then i do :rolleyes:

[dan2097]

Like I said. How is this any different than Nvidia users enabling 8xS on games where one card is powerful enough to use 4xAA/8xAF at 1600x1200 with AFR/SFR enabled? Its a good idea. But in many applications where the CPU the bottleneck. You can do this with SLI too. I dont see the dramatic difference here. The same argument can be used for Nvidia hardware with 8xAA and even 12x modes. Providing the framebuffer will allow it anyway.

Well framebuffer limitations wouldnt be a problem with ATIs approach and at 1600x1200 8xfsaa 16xaf that does sound like where you would start to run out of framebuffer on 256mb cards in newer games. I hope the reviews when they arrive compare the performance and image quality of Nvidias 8/12/16x modes to ATIs superAA modes

In all honesty 1600x1200 +more than 4 or maybe 6xfsaa is probably complete overkill. 1280x1024 or lower where your completly cpu limited would be a more normal use and in which case framebuffer size wouldn't be such a problem, nonetheless 16x and to a lesser extent 12x would still have a stupidly big hit, how does that compare to the competition having only effectively one card though :confused:

If supertiling really had exactly the same disadvantages as SFR and some more there would be no reason for ATI to implement it, and definitly no reason for them to implement it as their default direct3d mode, assumedly it must be generally better, or atleast scale more consistantly.

[HighTest]

If supertiling really had exactly the same disadvantages as SFR and some more there would be no reason for ATI to implement it, and definitly no reason for them to implement it as their default direct3d mode, assumedly it must be generally better, or atleast scale more consistantly.

Yes there is a reason to implement it. For the consumer, they see "one more mode"! Doesn't matter if there is exactly no further improvement over SFR as the consumer is duped by "feature count".

Very valuable marketting point even if technically there is no difference. Even if nVIDIA enables SuperTiling just to maintain the feature parity, ATI will claim "we did it first" even if nVIDIA did lab tests for example.

[ChrisRay]

If supertiling really had exactly the same disadvantages as SFR and some more there would be no reason for ATI to implement it, and definitly no reason for them to implement it as their default direct3d mode, assumedly it must be generally better, or atleast scale more consistantly.

Of course Super tiling scales better than their version of SFR. Their version of SFR isnt dynamic at all so it will never have optimal load balancing.

[dan2097]

Of course Super tiling scales better than their version of SFR. Their version of SFR isnt dynamic at all so it will never have optimal load balancing.
I heard the load balancing in SFR was simply software based, so if it made enoughof a difference once cpu overhead was taken into account to make it as good as supertiling they would surely of implemented it.

[ChrisRay]

I heard the load balancing in SFR was simply software based, so if it made enoughof a difference once cpu overhead was taken into account to make it as good as supertiling they would surely of implemented it.

Yes, you heard that from Neeyik. And frankly I'm not convinced. The reason ATI uses its tiling mode over its SFR mode is because its its tiling mode offers an advantage over its SFR mode. It doesnt change my point. Why use Scissors when their tiling is probably almost gaurenteed to load better than a non dynamic version of SFR? You're making alot of assumptions that SFR is inferior based on the fact that ATI is using Tiling for D3D.

Again. Tiling "Does" have the same disadvantages as SFR. It cant solve render to texture problems. It cant solve geometry scaling. Even 3dmark05 wouldnt benefit from tiling anymore than it would benefit from SFR. And no this is not a geometry scaling limitation in this case.

[emailthatguy]

dont oem's and vendors also need to carry 2 different sku's for xfire? i believe that is the case and correct me if im wrong, wont that signifigantly hinder how many actual stores pickup the slave cards?