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PCIe / SLI problem

karl420
By karl420
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Hi I have recently purchased a second gtx 970 to run in SLI. I noticed i get significantly lower performance when running SLI compared to a single card. I have literally sat on the internet for a couple of weeks now trying to find a solution to this problem and nothing seems to work for me. I have tried countless solutions like reinstalling the drivers, updating the bios, swapping GPUs around, changing Nvidia CP settings  etc.

 

My rig..

ASUS maximus VII ranger

850w Evga Supernowa

2x EVGA gtx 970 ftw

i7 4790k

 

 

I noticed that the GPU in the secondary PCIe slot is always running at x1 link speed instead of x8, even when using a single GPU in that slot. Thinking it was a faulty PCIe slot I returned my motherboard got a brand new one sent but nothing's changed. Could it possible be a faulty CPU? I don't have another one lying around to check it. What's strange is that I did not notice any difference in performance when running a single GPU at x16 in the primary slot compared to running a single GPU at x1 in the secondary slot.

 

Is this the reason I'm getting such a bad performance when running SLI?

 

Also I'm like 90% sure its not either of the GPUs as I've been running them separately in the primary slot for a week each with no issues

 

GPUz http://gpuz.techpowerup.com/15/07/17/3mc.png

 

the x1 does not change when running render tests or games

 

 

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Hi I have recently purchased a second gtx 970 to run in SLI. I noticed i get significantly lower performance when running SLI compared to a single card. I have literally sat on the internet for a couple of weeks now trying to find a solution to this problem and nothing seems to work for me. I have tried countless solutions like reinstalling the drivers, updating the bios, swapping GPUs around, changing Nvidia CP settings  etc.

 

My rig..

ASUS maximus VII ranger

850w Evga Supernowa

2x EVGA gtx 970 ftw

i7 4790k

 

 

I noticed that the GPU in the secondary PCIe slot is always running at x1 link speed instead of x8, even when using a single GPU in that slot. Thinking it was a faulty PCIe slot I returned my motherboard got a brand new one sent but nothing's changed. Could it possible be a faulty CPU? I don't have another one lying around to check it. What's strange is that I did not notice any difference in performance when running a single GPU at x16 in the primary slot compared to running a single GPU at x1 in the secondary slot.

 

Is this the reason I'm getting such a bad performance when running SLI?

 

Also I'm like 90% sure its not either of the GPUs as I've been running them separately in the primary slot for a week each with no issues

 

GPUz http://gpuz.techpowerup.com/15/07/17/3mc.png

 

the x1 does not change when running render tests or games

 

Link speed is likely the problem.

 

If you are running a single card, 1x is just fine. PCIE dumps out a TON of bandwidth, so the GPU can take it.

When running in SLI though, that may require more bandwidth than the 1x slot can give.

 

Look at the slot itself. Is it only wired for x1? Does the motherboard advertise the slot as higher than x1?

 

If worst comes to worst, you could try contacting Asus themselves.

~Judah

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Link speed is likely the problem.

If you are running a single card, 1x is just fine. PCIE dumps out a TON of bandwidth, so the GPU can take it.

When running in SLI though, that may require more bandwidth than the 1x slot can give.

Look at the slot itself. Is it only wired for x1? Does the motherboard advertise the slot as higher than x1?

If worst comes to worst, you could try contacting Asus themselves.

1x is not fine. It's too slow. PCIe doesn't dump that much bandwidth - PCIe 3.0 x16 transfers 32GB/s bidirectionally. 16GB per direction.

"It pays to keep an open mind, but not so open your brain falls out." - Carl Sagan.

"I can explain it to you, but I can't understand it for you" - Edward I. Koch

"I didn't die! I performed a tactical reset!" - Apollolol

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I didn't notice any performance difference even when running 1 card in the second PCIe slot at x1 which is really weird. I am able to get the same fps running 1 GPU at x1 in secondary PCIe slot as i do when running 1 GPU at x16 in the first PCIe slot. There should be a noticeable difference in performance but there is none. It's not a GPU-z bug as it appears to run at x1 in bios as well as other tools

 

Also did some benchmark tests and SLI seems to be working fine there scaling nicely and more or less doubling the score.

 

The issue occurs when I run games (tried W3, GTA5, Arkham Knight, Alien Isolation), e.g 1 card gets me 50fps on Witcher 3 on all settings maxed out whereas 2 cards is about 10-15 making it unplayable. Cards in SLI run at 50-60% usage. I have tried changing the power settings in both nvidia control panel and windows control panel with no improvement. 850W PSU should be able to easily handle this so pretty sure that's not the issue. SLI visual indicator is showing that it is working but not to its full potential.

 

I don't know much detail about the functionality of CPU but I've read somewhere that it's responsible for PCIe controller. Going to take it to a shop in the next couple of days as I don't have spare CPU to test with and they will :)

 

Also read about a PEG force x1 option in the bios but there isn't one in mine

 

Other than testing out a different CPU I'm all out of ideas. It's pretty unlikely that I would get a brand new motherboards with faulty PCIe socket twice haha...

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I didn't notice any performance difference even when running 1 card in the second PCIe slot at x1 which is really weird. I am able to get the same fps running 1 GPU at x1 in secondary PCIe slot as i do when running 1 GPU at x16 in the first PCIe slot. There should be a noticeable difference in performance but there is none. It's not a GPU-z bug as it appears to run at x1 in bios as well as other tools

 

Also did some benchmark tests and SLI seems to be working fine there scaling nicely and more or less doubling the score.

 

The issue occurs when I run games (tried W3, GTA5, Arkham Knight, Alien Isolation), e.g 1 card gets me 50fps on Witcher 3 on all settings maxed out whereas 2 cards is about 10-15 making it unplayable. Cards in SLI run at 50-60% usage. I have tried changing the power settings in both nvidia control panel and windows control panel with no improvement. 850W PSU should be able to easily handle this so pretty sure that's not the issue. SLI visual indicator is showing that it is working but not to its full potential.

 

I don't know much detail about the functionality of CPU but I've read somewhere that it's responsible for PCIe controller. Going to take it to a shop in the next couple of days as I don't have spare CPU to test with and they will :)

 

Also read about a PEG force x1 option in the bios but there isn't one in mine

 

Other than testing out a different CPU I'm all out of ideas. It's pretty unlikely that I would get a brand new motherboards with faulty PCIe socket twice haha...

In the Bios, Under "Advanced>SystemAgent>Graphics" Menu...

Go into the NB PCIE Configuration (This is different than the "Graphics" PCIE Slot selection)

Make sure that this is NOT on Auto, but on the Actual PCIE 3.0 setting.

 

By default on Auto, this feature had my 290 @ PCIE 2.0 16x, but had my GTX 970 @ PCIE 1.0 1x as a bug until it was changed off Auto mode.

 

Page 114 of your Manual - http://dlcdnet.asus.com/pub/ASUS/mb/LGA1150/MAXIMUS-VII-RANGER/e9798_maximus_vii_ranger_ug_v2_for_web_only.pdf

Maximums - Asus Z97-K /w i5 4690 Bclk @106.9Mhz * x39 = 4.17Ghz, 8GB of 2600Mhz DDR3,.. Gigabyte GTX970 G1-Gaming @ 1550Mhz

 

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Which PCIe slot are you actually using for the second card?

"It pays to keep an open mind, but not so open your brain falls out." - Carl Sagan.

"I can explain it to you, but I can't understand it for you" - Edward I. Koch

"I didn't die! I performed a tactical reset!" - Apollolol

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OK finally I found something, still just as strange though. I connected both cards and plugged my monitor into the second one. The second one is running correctly and the first one runs at 1x. So concluding the PCIe port that the monitor is plugged into runs fine. Any ideas what might be causing that?

 

Im using displayport

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OK finally I found something, still just as strange though. I connected both cards and plugged my monitor into the second one. The second one is running correctly and the first one runs at 1x. So concluding the PCIe port that the monitor is plugged into runs fine. Any ideas what might be causing that?

Im using displayport

Is this with SLI enabled or disabled?

"It pays to keep an open mind, but not so open your brain falls out." - Carl Sagan.

"I can explain it to you, but I can't understand it for you" - Edward I. Koch

"I didn't die! I performed a tactical reset!" - Apollolol

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both 

Try moving the DisplayPort connector over to the top card and see if anything changes.

"It pays to keep an open mind, but not so open your brain falls out." - Carl Sagan.

"I can explain it to you, but I can't understand it for you" - Edward I. Koch

"I didn't die! I performed a tactical reset!" - Apollolol

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I did. In both cases the card that the monitor isn't plugged into runs at x1 whereas the other one is running at x8. It changes when i swap the plug

That's strange. Any other cables you can try like DVI?

"It pays to keep an open mind, but not so open your brain falls out." - Carl Sagan.

"I can explain it to you, but I can't understand it for you" - Edward I. Koch

"I didn't die! I performed a tactical reset!" - Apollolol

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Just checked and it's the same when using DVI

Do you have another card to try? Maybe an older one? If not, I'd RMA the board if possible. Clearing CMOS may work too.

"It pays to keep an open mind, but not so open your brain falls out." - Carl Sagan.

"I can explain it to you, but I can't understand it for you" - Edward I. Koch

"I didn't die! I performed a tactical reset!" - Apollolol

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Do you have another card to try? Maybe an older one? If not, I'd RMA the board if possible. Clearing CMOS may work too.

 

Relating back to the monitor plug I didn't notice that GPUz swapped the list order of the cards so never mind that it's back to square one

 

So summing up either card will run at x1 in the secondary PCIe slot. I don't have any other GPUs lying around but seeing as both of mine run fine in the primary slot i doubt that they're faulty

 

I did RMA my board and got a brand new one but the issue still persists

 

I did things like clearing CMOS and updating the bios, as well as a number of drivers but nothing seems to work.

 

So as I mentioned above that my last guess is a fault with the CPU

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So as I mentioned above that my last guess is a fault with the CPU

It could be either the board or the CPU.

"It pays to keep an open mind, but not so open your brain falls out." - Carl Sagan.

"I can explain it to you, but I can't understand it for you" - Edward I. Koch

"I didn't die! I performed a tactical reset!" - Apollolol

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