GTX 680 SLI Issue: Worse performance than single card!!!

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Makaveliii

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Mar 3, 2013
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Hi Guys,

I am having a really weird problem right now. I recently purchased 2 different 680's off eBay. They both individually work perfectly fine. However, when they are SLI enabled, the performance is worse than the single card performance.

My Specs:

FX 8320 CPU
GIGABYTE GA-990FXA-UD3 Rev 4 Mobo
Asus GTX 680 Direct CUII OC GPU
MSI GTX 680 Twin Frozr III GPU
EVGA Supernova 750w Bronze
8gb DDR3
Windows 10 x64

I have tried numerous games with SLI enabled, including witcher 3 and fallout 4 but both perform worse than one of my single cards. By worse, I mean about 5 to 10 fps worse.

I know my CPU isn't the bottleneck, because I used to have a GTX 690 which gave me amazing performance and my CPU utilization never goes past 70 or 80. I know it isn't the PSU, because I benchmarked the cards with furmark with both pulling about 100w tdp, and were at 99 percent load, with no problems for about an hour. It isn't the temperatures as the card on top reaches 75degrees celsius max and the one at bottom only 64 through furmark. I tried installing different driver versions, and doing clean installs of them. I tested all the PCIe lanes and they were working fine. I also checked the PCIe bandwidth through GPUz and it was showing @x16 2.0 for both cards. I'm completely at a loss and this is turning out to be the biggest waste of money ever.

I'll try test the cards in sli in a friend's computer, and will try different SLI bridges and swap out the cards into different PCIe slots.

Another thing to note also is that when playing witcher 3 for example, the load on both gpu in sli is only 50% compared to 99 in single GPU mode.

Could it be a defective card? The MSI 680 also never went past 50 load when i first got it but I re-installed drivers (downgraded from 664 to 361) and the card was at 99% for every game/benchmark.
 
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Makaveliii

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FYI, I have the SLI bridge enabled and also SLI enabled in nVidia control panel. I have also gone into the power options and ticked high performance with no change. Will try installing Windows 7 and report back on results.
 
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Makaveliii

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They are the same GPU and both have 2gb VRAM each so should be compatible with each other.
 
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Makaveliii

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That's not true at all. Look up witcher 3 benchmarks with these 2 cards. They are hitting 60 fps easily. If you are suggesting less than 30fps is normal for 2 680s then take a look at the benchmark. There is definitely something wrong with my setup which is why I'm looking for answers
 
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nicholausrossi

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I'd be interested to see your results. I'm currently on W7 with 680 SLI and I was considering moving to W10. Here are some current benchmark scores:
70v8kWz.jpg


Edit: Have you set power management mode to "Prefer High Performance" in the NV control panel? The default setting is adaptive.
Edit2: Try disabling PCI-e link state power management as well. Link: http://
 
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imrazor

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Because they are different cards, they are probably operating at different speeds. Perhaps there is some sort of synchronization problem between them. Have you compared the GPU and memory clocks of both cards with something like MSI Afterburner?
 
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Makaveliii

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Yes I noticed this. Sometimes the msi would be clocked higher when I monitor it in game and other times it is the same for both. I researched sli extensively before buying the cards and the info I received everywhere was that the higher clocked card would automatically clock to the speeds of the second card. Also worth noting is that although both cards are 2gb, in gpuz I saw one was manufactured by Samsung and the other by a different company. I don't know how significant this is, probably isn't as it's all gddr5.
 
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imrazor

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I've heard conflicting reports about whether you can mix and match different cards in SLI. Some people say there's no problem using different cards, but sometimes I run across people claiming that it doesn't always work. That's why I've been hesitant to get another GTX 670 and SLI it with my existing card. The only suggestion I can make that might help is to disable SLI, use MSI Afterburner to manually synchronize the cards (ie, lower the speed of the faster one to exactly match the slower card), then reapply the SLI setting. I'm not sure that'll work, but it's the only suggestion I can make after everything's that been tried so far.
 
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imrazor

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Some other thoughts: have you tried swapping PCIe slots? Are you sure your PCIe slots are configured to have at least 8 lanes available in each slot you have your GTX 680's plugged into?

EDIT: Nevermind, I saw that you checked the bandwidth with GPU-Z. Just to confirm, though, your cards are in the slot closest to the CPU and the third PCIe x16 slot from the CPU, right?
 
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Makaveliii

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With my motherboard, only the first and third are x16 which is what I'm using. If i used the other PCI, it would show x4 in GPUz. I went from windows 10 to windows 7, and the performance was the same so no difference made there. However, I tried running 2013 Tomb Raider max settings 1080p with a single card and got about 70fps in benchmark. In SLI, I got 120 fps in benchmark. I tried running the benchmarks across 3 1680x1050p monitors and got 118fps in SLI. I tried shadow of mordor with 1 card at max settings on 1080p and got around 30fps, but 70-80fps in SLI. i Was only getting 50fps for this game with a 690. This has left me really confused. How is that even possible. Apparently, shadow of mordor scales more than 100%, and the 690 which is essentially 680 sli is getting lower fps. Only these 2 games are using both cards at 99% usage, whereas all the others use them at around 50% apart from dead rising 3, where 1 card is 99% and the other is 0%. Could it be optimisation issues? How do I go about this and how do I force 99% usage on both cards? I know there is a way to do this.
 
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Makaveliii

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I have seen online mixed opinion about the SLI scaling on witcher 3 and the SLi profile for it. Some people think it is extremely well optimised for their sli setup whereas others think the game should not be played on SLI. When I had the 690, on max settings at 1080p including hairworks settings I was getting solid 45 to 55 fps. This is probably because the chips were well in sync with each other. I will try sync both my cards speeds and report back. I have also tried 3 different SLI bridges with the same results so that rules that out.
 
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rossinator

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I can Skype with you this afternoon and go through some of your settings. PM me your Skype name and I'll add you as a contact.
 
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Makaveliii

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Thanks for the offer but I'm based in the UK where its past midnight so I would be unable to Skype. Could try tomorrow? I tried the witcher 3 with lowest possible settings and the fps shot up. Is this a CPU bottleneck? Maybe the CPU can't handle 2 gpu at same time?
 
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rossinator

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I would recommend taking a look at your bios settings to ensure your cpu is still still overclocked. If it isn't, 4.5ghz @1.45v is a pretty good starting place.
I have a suspicion that we could flash a new vbios on those cards (so they're identical cards eg 2x EVGA Classified FTW 2GB GTX 680s. We can even do a custom overclock and fan profile so they run at 1200+ core 24/7 and +500mhz on your memory. My 680s at those clocks are about 800 points away from 780 SLI in 3Dmark.
 
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Makaveliii

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Flashed my BIOS to the latest version F3, made no difference. I'm not willing to go as far as flashing my GPUs, as I don't want to brick them. Tried the 3dmark benches, and benches such as firestorm utilise both GPU to 90-99% all the time. On my benches, the scores I got were as good as an i5-4590 with gtx 970, bearing in mind I'm running a fx 8320. Therefore, SLI is fully working to its potential when the application is utilising it properly. I guess it is just the games then which I'm running that has piss poor optimisation.

I thought the witcher 3 was properly optimised aswell. I will test the new assassins creed now and report back.
 
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Makaveliii

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Just tried AC syndicate and surprisingly, for a Ubisoft game, it is extremely well optimised for SLI. both GPU load above 90 %. I guess it is just that some games simply run far better on a single GPU.

Anyway, thanks for all of your help guys.
 
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