Frequent_Flyer

Why am I getting poor performance with 4 graphics cards?

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I have 4 GTX 960s running in the computer.  However, I still get stuttering and whatnot.  I feel like I should not be having problems with performance as I would figure four should let me do about anything I want.  Is there something specific that I am missing?  Like maybe somehow only one of the graphics cards are being used? That probably isn't the case, but I don't know so any help would be appreciated.

Thanks!

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Posted (edited)

P3D doesn't really scale that well with SLI never mind Quad SLI.

So in reality you will be limited by the performance of your card series, which in this case, a 960 is not that powerful.

You also don't mention the rest of your system. P3D is still very dependent on CPU performance.

 

 

Edited by GHarrall
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I realized there are 4 GTX 1080s not a 960s... which I guess is not even relevant anymore considering what you just said about scaling.  That is very unfortunate that it doesn't scale very well... Does it scale at all or just very minimally? This is not my computer, so I will need to respond with what the other specs are in a bit when I find out.

 

Thanks.

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I was not even aware that four graphics cards could be used at the same time :blink:

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Yeah, supposedly the setup has it so that they are each used individually and not linked.  There are 4 main displays and 1 display for the control panel that need to be used at maximum performance and realism so that is why 4 were purchased.  I still think that there 4 graphics cards should definitely work better, which is why they were bought, but maybe in a different configuration that isn't typical? 

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Using 2 graphics cards gives lower than expected performance gains, using 4 is overkill. I also thought Nvidia officially disabled support for anything over 2 except for heavy duty work stations? It doesnt help that P3d is still primarily a CPU driven program. 

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Posted (edited)
59 minutes ago, Frequent_Flyer said:

Yeah, supposedly the setup has it so that they are each used individually and not linked.  There are 4 main displays and 1 display for the control panel

I installed 3 x 1080Tis, originally not SLI'd, with the intention of putting one projector on each. The result was not satisfactory -- too stuttery.

With all three on one 1080Ti and the other two cards actually unused, it was better! But best for smoothness was with the three projectors all on one card, and the three SLI'd. Definitely smoother than without SLI, but no faster.

There's also a small "boot" monitor on the same card, on the DVI connection (to ensure it is chosen by the BIOS for booting).

The three video cards seen to get used about evenly, but rarely more than 20% on each. The limitation on performance is always Processor Core 0, which is running at 100% solidly in all the denser situations, like EGCC with 100+ AI aircraft around.

My system is also a 7900X, with all 10 cores running at 4.8 GHz, and HT off. The memory is 4 x 8GHz, rated at 3400 Hz but running at 2800 for stability. 4 sticks is better with quad memory, making maximum use of the processor memory bandwidth.

Pete

 

Edited by Pete Dowson
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Anything passed two cards in SLI is no longer supported with Nvidia.  You could use 2X1080 in sli but will still be limited by the 8gb vram.  If i were you and wanted the best, sell those cards and upgrade to the 1080 ti with 11 gb of vram or wait a month for the new Nvidia cards to be annouced.

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The motherboard has two PCI slots each one capable of 16x or 8x lanes, one GPU installed will run on 16 lanes passthrough two GPUs installed each GPU will now only run on 8 lanes each + 2 16 lanes the same as one. This is why Nvidia don't see the point of SLI now with the power that the latest single GPU has.

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3 hours ago, GHarrall said:

P3D doesn't really scale that well with SLI never mind Quad SLI.

So in reality you will be limited by the performance of your card series, which in this case, a 960 is not that powerful.

You also don't mention the rest of your system. P3D is still very dependent on CPU performance.

 

 

I have an Intel Core i7-7700 CPU @ 3.60 Hz.

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Posted (edited)
1 hour ago, bgpearce01 said:

Anything passed two cards in SLI is no longer supported with Nvidia. 

Well my 3-way SLI is noticeably smoother than no SLI, and the loading on the three cards is about the same on each -- around 20% At present I am processor limited.

21 minutes ago, rjfry said:

The motherboard has two PCI slots each one capable of 16x or 8x lanes,

Interesting. Mine has three identical slots for GPUs, and I'm sure the spec says they are all 16-bit.

21 minutes ago, rjfry said:

This is why Nvidia don't see the point of SLI now with the power that the latest single GPU has.

Certainly the performance, frame-rate wise, isn't any better with the 3 linked up, but it is smoother than with just the one card in use and no SLI. And it is certainly much smoother than with each projector on its own card.

What is killing my performance is the inablility of P3D to drive three windows (albeit docked), all at 1080p (not 4k), without a 50% hit on frame rates. But it is still good everywhere except at dense airports like EGCC, EHAM, LFPG, with something near the amount of AI Traffic I like to see.

Pete

 

 

Edited by Pete Dowson
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3 minutes ago, Pete Dowson said:

Well my 3-way SLI is noticeably smoother than no SLI, and the loading on the three cards is about the same on each -- around 20% At present I am processor limited.

Interesting. Mine has three identical slots for GPUs, and I'm sure the spec says they are all 16-bit.

Certainly the performance, frame-rate wise, isn't any better with the 3 linked up, but it is smoother than with just the one card in use and no SLI. And it is certainly much smoother than with each projector on its own card.

What is killing my performance is the inablility of P3D to drive three windows (albeeit docked), all at 1080p (not 4k), without a 50% hit on frame rates. But it is still good everywhere except at dense airports like EGCC, EHAM, LFPG, with something near the amount of AI Traffic I like see see.

Pete

 

 

Each projector of mine has its own card just like yours, so hopefully that is the best set up.  Could you explain what you mean by it being "smoother"?  I take smoothness to be the opposite of having stutter.  However, from previous comments, stutter was said to have been a direct result of the CPU and not the GPU. But in your case, you say that having each projector on its own card (GPU) makes it more smooth for you.  I am new to all of this stuff and am just trying to get terminology down.

Thanks :)

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I think your CPU is the main factor.  3.6 ghz?  Have you tried an overclock?  At least 4.3 -4.4 should help a lot

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Posted (edited)
54 minutes ago, Pete Dowson said:

Well my 3-way SLI is noticeably smoother than no SLI, and the loading on the three cards is about the same on each -- around 20% At present I am processor limited

I have yet to see a mainstream motherboard use 3 X 16 pci lanes(at the same time).  Once you go past two you will need to cut them down to 8.  The architecture itself is limited to 64 lanes and you need to keep some open for data i/0 etc.  Regardless this is hardly a bottleneck in this situation.  You could probably pull a card and see the same if not better performance using 2.

 

Regarding using 3 or 4 video cards.  Starting with the pascal series cards (1070, 1080 etc), nvidia is restricting the use of more than 2 cards in sli.  The return and complexity of drivers after 2 cards is just not worth it.  I wanted to mention this incase anyone was thinking of adding a third or fourth card.  It would be a total waste of money and even if it did work in P3D, it wont in anything else such as games.  If you are running older 9 series of even 7 series nvidia cards, sure you could theoretically run 3 or 4.  But 2X gtx 1080 ti's will beat ANY 3 or 4 card variations.  Not to mention vram is not pooled so as you decrease the vram you will start to see stutters.

Edited by bgpearce01

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This post headline initially made me chuckle.

 

It made me think of this analogy.

Your 4 graphics cards are the Autobahn, where speed limits in many places are non existent, ergo, you can go as fast as you want.

 

P3D is your 1992 VW rabbit. 4-cylinder 1.8 litre 4-speed rocketship that tops out at 120kph.

Try as you might, you are never going to reach the top speed you imagine in that car despite having all the space in the world to do so. Old engine, old limits...

 

 

As many others have said, it's far better to upgrade the 4 old cards to one current gen card with as much VRAM as possible.

Happy motorin' 😉

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