SLI for FSX: Debunked

[BimmerCop 332]

Hey Srdan, I know you will probably look at this thread... I read on another thread where you stated that SLI DOES benefit FSX/P3D when used with a visuals only setup (no cockpit, VC, etc).

 

Can you elaborate on this? This will benefit people who do home cockpits and use one PC for visuals only, like myself.

 

What type of performance increases are we looking at in these type of situations?

 

Sent from my Galaxy Nexus using Tapatalk 2

 

 

 

Brain fart!!! Nevermind this thread, mods can delete it. I just noticed Srdan had already started one on the same topic. Hahahah my bad!

 

Sent from my Galaxy Nexus using Tapatalk 2

 

 

[westman 257]

Hi

Did a test with a modifed Dazz Gpu mark with 3wievs setup for warpalizer.

Cards 680 and 690 , the 690 was 40% faster in that test

Need more time to finsh the tests

 

hasse

 

[Kosta 122]

Can you elaborate on this? This will benefit people who do home cockpits and use one PC for visuals only, like myself.

 

The tests we did some time ago, the user was Descend Descend, he has two GTX580s, and I we were making comparisons with my own computer, and in the end, measured up to *almost* double FPS (if I remember correctly) in some scenarios.

Yes, this will only work for scenery-view only, as apparently, SLI got broken through various cockpits, so yes, only for cockpit builders.

 

Brain fart!!! Nevermind this thread, mods can delete it. I just noticed Srdan had already started one on the same topic. Hahahah my bad!

 

Really? Where?

[jjjallen 37]

Prove it helps as I'm itchy to get another MSI680 Lightning GPU. Cheers jja

[jjjallen 37]

Cool Word Not Allowed - I didn't need the $$ anyway. Cheers jja

[martin-w 3,235]

double post, deleted.

[martin-w 3,235]

SLI got broken through various cockpits, so yes, only for cockpit builders.

 

Really! My understanding was, from everything Phil Taylor said, that FSX was not coded to make use of SLI in the first place.

 

SLI does seems to be advantageous marginally at very high res, or perhaps it's an advantage for those with multiple monitor set-ups, but I'm very dubious that "it got broken". It was never a feature that was present, to get broken, if it wasn't there in the first place, how can it get broken?.

[goates 576]

It was never a feature that was present, to get broken, if it wasn't there in the first place, how can it get broken?

 

At a basic level programs don't have to specifically do anything to make use of SLI/Crossfire. It is handled internally by the video driver such that the game doesn't need to know anything about it. However, there are things the developer can do to make better use of SLI/Crossfire. There are also things the developer can do that cause problems with SLI.

[KingGhidorah 209]

Really! My understanding was, from everything Phil Taylor said, that FSX was not coded to make use of SLI in the first place.

 

SLI does seems to be advantageous marginally at very high res, or perhaps it's an advantage for those with multiple monitor set-ups, but I'm very dubious that "it got broken". It was never a feature that was present, to get broken, if it wasn't there in the first place, how can it get broken?.

 

I think you are correct about this. A test as described above between one user's computer with a single card as it compares with some other guy's different computer running SLI seems like a less than ideal comparison. People who have very large res displays or are using surroundscreen setups can very easily see a difference between running two cards, versus running one card, simply by trying it with SLI on, and SLI off--and I'm not talking scenery only home cockpit builds, I'm talking a standard virtual cockpit view, with a virtual instrument panel and all. The difference is very noticeable. SLI doesn't "break" anything, and I'm not sure what has been "debunked" or by who.

[martin-w 3,235]

But my point, is that nothing was ever broken. No cockpit panels or gauges have ever broken it. Simply because Aces never coded FSX to support SLI in the first place.

 

I thought Phill Taylor had made that clear.

 

Don't get me wrong, if you are right, and SLI does have the potential to benefit FSX, then that's great, but I feel it would overturn everything we thought we understood about SLI and the sim.

 

Like all tests like this, we can't rely on just one experiment. The results would have to be confirmed, replicated by others.

[KingGhidorah 209]

<p><p><p><p>

OK, now I really slowly am feeling insulted. You really think that I'm testing FSX since yesterday?? You think I wrote my guide just out of pure amusement and hit a certain success rate because I just wrote the stuff out of blue skies? But, since you are relatively new to the community, I'll just take your comment with a grain of salt.

If you are actually saying that SLI makes no difference unless somebody is using a scenery-only home cockpit setup, then I disagree with you;I fly in the VC and I use SLI on my system with massive resolutions but only moderate 8xs/16x af, dx9, and the results are very clear to me. If I have SLI ON, things perform wonderfully. If I disable SLI, keeping everything else the same, the simulation suffers from massive stuttering and low fps. I hope I'm not misunderstanding what is being discussed here because if that isn't what you are refuting then I guess we have no disagreement--Maybe you guys are talking about something else, because I would have assumed you would agree with these observations.

[goates 576]

But my point' date=' is that nothing was ever broken. No cockpit panels or gauges have ever broken it. Simply because Aces never coded FSX to support SLI in the first place.

 

I thought Phill Taylor had made that clear.[/quote']

 

Read my post above. At a basic level developers do not need to do anything for their games/sims to use SLI. SLI and Crossfire are handled internally by the video driver, which can happen without the program ever being aware that there is more than 1 video card installed. Phil Taylor actually points this out in one of his blog posts I believe.

 

Having said all that, developers can optimize their program to make better use of SLI/Crossfire. Some programs, like FSX apparently, can also do things that hurt the use of SLI setups. Compounding the problem with FSX is that as it is a CPU bound sim, older CPUs would have held back performance long before any calls were made to the video driver. Meaning that only recently have we got to the point where CPU power has increased enough for more GPU power to become useful for more people. Those with very high resolution monitors or multiple monitors had already seen small improvements.

[goates 576]

Exactly why it is working in FSX really, and exactly why it works under certain scenarios only

 

Probably old code in FSX used to draw the panels making use of older DirectX functions that don't mix with SLI. Or something along those lines anyways.

[martin-w 3,235]

OK, then explain it to me, why did we see higher FPS with two cards, compared to one? Same system, same computer, same screen... results weren't lying.

 

I can't Word Not Allowed, and given that most of us on this forum have a great deal of respect for you, it's very interesting. The only thing I can think of is that I haven't recalled Phill Taylors words accurately.

 

Compounding the problem with FSX is that as it is a CPU bound sim, older CPUs would have held back performance long before any calls were made to the video driver. Meaning that only recently have we got to the point where CPU power has increased enough for more GPU power to become useful for more people. Those with very high resolution monitors or multiple monitors had already seen small improvements.

 

Now that would perhaps make sense. Sorry I missed your previous post.

 

And that. Exactly why it is working in FSX really, and exactly why it works under certain scenarios only - I was hoping I could reach Nvidia to look into the driver, why it doesn't work with certain cockpit kinds, but it was a long shot.

 

Could it be related to the gauges? Default FSX aircraft you see a boost. But in the NGX, with it's complex gauges, complex coding, you see no boost. Just wounder if it's the multitude of complex gauges that are in some way the issue?

 

Sorry if I'm talking rubbish, just thinking aloud.

[goates 576]

I can't Word Not Allowed' date=' and given that most of us on this forum have a great deal of respect for you, it's very interesting. The only thing I can think of is that I haven't recalled Phill Taylors words accurately.

[/quote']

 

Here's Phil's post regarding SLI.

 

http://blogs.msdn.com/b/ptaylor/archive/2007/03/03/fsx-more-on-sli-and-multi-core.aspx

 

He mentions one or two things that can break SLI in a game. Looks like FSX might be running into one or both of them.