Unity SLI or Crossfire

Hi All,
We're working on an installation piece with Unity and have some questions. Here are the specs on the project:

We need a 1920x1920 signal from one computer. The unity app has continuous visual elements that animate over time across the entire 1920x1920 surface. As a result, we're thinking most likely one unity application.

the video signals will be handled by two HD projectors.

The application itself is pretty intensive and requires a good amount of horsepower. As a result, we're looking into the possibility of using SLI or crossfire to help keep frame rate high.

So I think our initial questions are:

1. Is Unity capable of reaping the benefits of SLI or Crossfire? If so, any information would be greatly appreciated (re SLI vs. crossfire).

2. We can't seem to enable SLI or Crossfire when dual spanning is active in either the nVidia or ATI control panels. Any workaround for this? Meaning, has anyone been able to have dual span mode WITH SLI/Crossfire?

Anyone with multi display and/or unity->HD projectors experience, would love to hear from you.

Thanks much in advance,

d

 

I'm not sure what your timeline is, but I've heard from an acquaintance with a test board that the next series of Nvidia cars. (3xx series) will be faster than SLI just using one card. The card should be coming out before the end of the year... hopefully.

 

Unfortunately, our deadline for testing, etc. is mid-december. We have 4 machines right now that we're testing with:

corei7 3.4GHz processors
xp 64 bit
8 GB ram

machine 1 - 2 GTX 295's
machine 2 - 3 GTX 285's
machine 3 - 2 Radeon HD 5800's
machine 4 - 2 Radeon HD 4800's


However, i don't think we can run monitor span SLI. Since monitor span is key, we may have to axe SLI/Crossfire anyways.

Anyone been able to run span mode with SLI?

d

 

1. if you write your own shaders for everything. otherwise no, unity shaders are developped with cross platform in mind and sli / cf are a windows only thing

2. I think the 190.x drivers on vista on the nvidia side fixed this issue actually with sli + screen span.
I'm on single card span at the moment, where its logically no prob sorry

 

I´ve got 2 x Geforce 8800 GTS´s running in SLI mode (Windows XP, latest Detonators)

So far I haven´t noticed that the SLI is used by Unity.

Tested by disabling and enabling the cards/SLI.

No performance gains there ?

Cheers !

 

engines never care about sli.
SLI to the engine appears like 1 gpu, thats the whole point behind it

But depending on the sli mode, it makes a difference in behavior.
Unity luckily has very few shaders that reference data from the last frame. if it had that more commonly you would see a performance degrade actually as the cards wouldn't be able to render upfront if they are set to render alternative frames.

 

Dreamora,

I for example have an Alienware M17X notebook with dual SLI Geforce GTX280M in there

You state that unity could benefit from SLI if you write your own shaders. Could you please give a little more information about this? Does that mean that a specific shader could be written which makes for example the DIFFUSE FAST shader suddenly work a lot faster because the second GPU will help ?

Are all the standard shaders in unity then not getting any benefit from SLI ?


regards,

Bart

 

most shaders don't have inter-frame dependencies and thus don't require any changes.

But there are shaders that depend on previous frames and these shaders need to be rewritten to use the correct frame.


As for the alienware notebook: anyone having that much money won't buy games that don't have HD quality on textures etc because "bad looking games don't suite cool kids with money S***ting parents" (harshly put but a reality that drives the development of no brainer games with high end visuals)

 

I'm sorry, but I'm

1) Not a kid
2) My parents don't S*** money
3) I work hard programming and wanted
4) absolutely the fastest possible laptop I could find just because I want to have to wait as little as possible compiling (therefore quadcore extreme)

It had to be a notebook to please my wife since she doesn't like me to be in the office from 8am tot 23PM or later. So at evenings I sit in living room with the notebook.

I know the gfx in this machine are quite fast, but I don't PLAY games. I create software and was just interested to see the full power of the notebook.

So if I create 100 objects in a scene and only use the normal bumpmapshader without any fullscreen effects, then that SLI should accelerate my rendering ?


regards,

Bart

 

Yupp, with this kind of shaders it will be SLI enabled.
Its primarily the "PostFX" class of shaders that has frame dependencies and has to be chacked / modified


As for the statement above: I know that others potentially buy this one too.
Though I fail to see how SLI in notebooks helps for anything else than developing burnt skins and back problems, because its still an M card in sli. As such you can hope that a 280M SLI combo is able to achieve somewhere GTX280 speed.

As for the quad core: Thats a valid point at least if you use .NET / C++ and have Xoreax InvisiBuild. Otherwise the quad won't help you anything as neither Unity nor Visual Studio use multiple cores for compiling. A single core with higher clocking would therefor be the better solution
My Core i7 in the desktop for example primarily shines due to multitasking and when I use L3DT / Texture Maker / PhotoShop ... that are the only cases that really use more than 2 cores, just to give you an idea on the direct use of multicores by now.
I'm mentioning that because the notebook market is about to change quite a bit with the introduction of USB 3.0 and the Core architecture and I wouldn't waste too much money on "highest end" at the time if you don't have very strong reasons (audio,video,photo editing or scientific work with CUDA) for it

 

1 answer for that cpu stuff -> H264, premiere, encore, after effects, ....

 

Hehe yeah media encoders are multicore capable and benefit from it

Thats why I put those in in case you use them.
For compiling and unity dev multicore has very little use, thats why I put that part in