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SLI: some questions.

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magellan

Member
Joined
Jul 20, 2002
I read over on the SLI FAQ on Nvidia's website and they mention two modes of SLI: AFR and SLI AA. If a game doesn't support SLI can you still use the SLI AA mode with it?

I'm surprised how few titles actually support SLI, somewhere around 370 and some of those titles are now irrelevant (who really needs SLI to play Doom3 or Deus Ex: Invisible War or Tron 2.0 or UT2004 or COD: MW3 or Silent Hill: The Room?).

Is it true SLI support is decreasing because of the increasing consolification of the video gaming world?
 

Soulcatcher668

Member
Joined
Jan 2, 2012
With DX-12 and Vulcan, SLI/Crossfire should become more readily available. They will not be crossfire and SLI anymore as this control will be at board level.
You will even be able to mix Nvidia and AMD cards.

Unfortunately this will not be backwards compatible. Games that do not do SLI/Crossfire now will not magically get support under DX-12/vulkan.
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
I dont think SLI support really had much going for it.. Look at Steam stats and see how many people % wise use multiple GPUs... not many at all. Surprisingly low in fact.

Multiple GPUs, to me, was for the extremely high resolution or extremely high FPS which a single card cannot handle. Otherwise, it was for the 'e-peen'. I mean what isn't to love with NEVER having 100% scaling (typical is what 50-90%, sometimes NONE), double the power use, and more hassle all around?

I really don't think it has anything to do with the, as you said "consolification" (is that a word?!!) of the video game world.
 

Janus67

Benching Team Leader
Joined
May 29, 2005
It's a 'word' that is used a lot in the pc games industry by critics etc.

As others said, for the vast majority of games multi gpu has very limited benefit. Sometimes you get some good scaling and more fps. But just as often there's no scaling or there's flickering or texture issues etc.
 

Zantal

Member
Joined
Mar 19, 2009
SLI AFR is alternate frame rendering which is the regular SLI (one card draws frame 1 the other draws frame 2) to increase performance.

SLI AA is an option you can enable in case the application does not support SLI AFR, with that you can basically crank up the antialiasing in the control panel
It doesn't increase performance it only increases quality while retaining the same performance.

My thought on why it is not so popular is because

Devs and nvidia need to put a lot of effort compared to the user base they are making it for (as stated above)

The systems with SLI are less because the gaming experience is worse.

They tried to make SLI a reality so they could try to sell us double the amount of cards, now we are shifting towards double the price for 1 really beefy card.

As of the DX12 remark, engines will have the capability of accessing multiple devices (before they couldn't as the "device" was really abstract)
still multi gpu support will need to be implemented, but don't expect 100% scaling anyway (and I don't believe it will be that much better anyway if at all)
 

jaymz9350

Member
Joined
May 13, 2006
The systems with SLI are less because the gaming experience is worse.
I'd say it's more to do with price and power draw. My experience is the same as when I ran single cards.

That said if the 980ti was out when I upgraded I'd of went that route over 970 SLI
 
OP
M

magellan

Member
Joined
Jul 20, 2002
With DX-12 and Vulcan, SLI/Crossfire should become more readily available. They will not be crossfire and SLI anymore as this control will be at board level.
You will even be able to mix Nvidia and AMD cards.

Unfortunately this will not be backwards compatible. Games that do not do SLI/Crossfire now will not magically get support under DX-12/vulkan.

Does Ashes of the Singularity support the DX-12 multi-GPU mode? Will all games coded for DX-12 have to support the DX-12 multi-GPU mode?
 

Janus67

Benching Team Leader
Joined
May 29, 2005
Does Ashes of the Singularity support the DX-12 multi-GPU mode? Will all games coded for DX-12 have to support the DX-12 multi-GPU mode?

Yes and No. Ashes does, the code is available for multi-gpu but requires effort on the part of the developer to implement.
 
OP
M

magellan

Member
Joined
Jul 20, 2002
Yes and No. Ashes does, the code is available for multi-gpu but requires effort on the part of the developer to implement.

So the multi-GPU benefit of DX-12 isn't transparent to the developer? They have to code their game specifically to take advantage of it? That's disappointing.
 

EarthDog

Gulper Nozzle Co-Owner
Joined
Dec 15, 2008
Location
Buckeyes!
Sure it does... you will want to overclock even skylake to remove the 'cap'. How much will vary by title. It isnt typically much, a few to several fps. But again, it depends on the title, res, settings, cards, cpu, etc...
 
OP
M

magellan

Member
Joined
Jul 20, 2002
Sure it does... you will want to overclock even skylake to remove the 'cap'. How much will vary by title. It isnt typically much, a few to several fps. But again, it depends on the title, res, settings, cards, cpu, etc...

Do you think there's any chance multi-GPU setups will be more viable w/DX12 and Windows 10? Or is it just empty hype?
 

Zantal

Member
Joined
Mar 19, 2009
For me it is just empty hype, I used to think of SLI as some kind of magic technology when I was younger, mainly because I didn't know back then how all this stuff works.

The problem lies at its core, no matter how much support there is for multi gpu or how good you are at optimizing it you are still fighting a battle you cannot win
which is to make 100% use of both cards, and you simply cannot do it with modern games.

It used to be somewhat better when we didn't have all these fancy effects and games consisted mostly of geometry and basic shading, back then SLI worked in a manner to evenly split workload on the gpus by using some complex algorithms which managed to calculate how much of the screen each card had to render to have similar loads.

Today with all these new fancy effects it just isn't possible anymore, Parallelism is a b***
There are some tasks which can be easily parallelized, such as rendering, this is why we have gpus with lots of "simple" cores.
this scales well proportionally to load and available power (removing constraints such as memory speed resolution different kinds of shaders etc etc)

If you were to add another gpu the only way to make 100% use of it would be to know in advance the frame it needs to render, and since we haven't invented time machines yet you simply cannot render a future frame.

So what we resort in doing is to delay the first frame. basically you are always 1 frame behind in respect to a single gpu config.

Now you would think this is a pretty solid tactic and it would scale 100%, well it would if you manage to keep frame times always exactly the same, you could achieve that with frame pacing or dynamically adjusting load (real time frame scaling)

You can clearly see that to solve 1 problem (low fps) you are creating many others, this is why from now on my philosophy is to get the beefiest card possible.