GPU's defaulting to x8 PCI E lanes despite enough for 16x being available

[Jewish-Man]

Hello. I recently got a new laptop to use for school that is also pretty well equipped for gaming. As I was using this laptop, I noticed something strange. I was getting better performance in games on my laptop rather than my desktop. How could this be? My desktop is more powerful in every way.

 

Some research into my bios has revealed that my GPU's are only using 8 PCI-E lanes a piece when I have 40 total available. I am using an m.2 drive as my os drive as well. With all of these PCI-E devices together I should only be running 36 lanes actively (16+16+4=36). After spending awhile just browsing through the BIOS, I was unable to find anything that appeared to allow me to change the number of PCI-E lanes that each slot was using. Am I just missing something?

 

I know this isn't my only issue causing performance issues most likely, but it is definitely an issue. 

 

My system specs are included in the spoiler. I have confirmed that I am using the latest version of the BIOS available for my motherboard dated 18JULY2016.

 

Thanks for any help in advance!

 

Spoiler

• CPU
  Intel i7 6850k @ 3.9 GHz
• Motherboard
  MSI SLI Plus X99S
• RAM
  Corsair Vengeance LPX 32GB (2x16GB) DDR4 2400
• GPU
  Gigabyte G1 gaming GTX 1080 x2 SLI
• Case
  Coolermaster HAF X
• Storage
  Samsung 950 pro 512GB
• PSU
  EVGA SuperNOVA 850 T2
• Display(s)
  Asus PG278Q @ 2560X1440 144Hz Via Display Port, Asus VG248QE @ 1920x1080 144Hz Via DL-DVI
• Cooling
  Cooler Master Hyper 212 EVO
• Keyboard
  CORSAIR K70 RGB RAPIDFIRE Mechanical Gaming Keyboard
• Mouse
  Logitech G900
• Sound
  STEELSERIES Siberia 800
• Operating System
  Windows 10 Pro 64 bit

2

 

[Enderman]

No it is not an issue.

A GPU doesn't even use 8 lanes.

[Leeberator]

It could have to do with the slots the cards are in. Some boards have x16 slots that only operate at x8 speeds depending on what's plugged in where. Your 40-lane CPU makes this less of a possibility, but it's definitely still on the table.

 

Check your motherboard manual for a list of PCIe modes.

[Jewish-Man]

1 minute ago, LeeTheENTP said:

It could have to do with the slots the cards are in. Some boards have x16 slots that only operate at x8 speeds depending on what's plugged in where. Your 40-lane CPU makes this less of a possibility, but it's definitely still on the table.

 

Check your motherboard manual for a list of PCIe modes.

All of my PCI-E lanes are gen 3 16x slots as far as I am aware. When viewing the slots in the BIOS it also labels the slots as something along the lines of "PCI-E 3 x16 slot running at x8" where the GPU's are slotted and the same thing except x4 where the M.2 drive is slotted.

[Brooksie359]

No way that the pcie lanes is the issue. 8 lanes of pcie 2.0 is enough for basically all modern graphics cards. I am guessing your lanes are 3.0 in which case it is out of the realm of possibilities.

[VolkA]

Wait. So you have 2 1080 running at SLI? I thot when 2 running SLI, the lane will be x8 and x8? Or did I remember it wrongly.

[Brooksie359]

8 minutes ago, VolkA said:

Wait. So you have 2 1080 running at SLI? I thot when 2 running SLI, the lane will be x8 and x8? Or did I remember it wrongly.

It is with all z series mobos. They have an x99 mobo with a cpu that has more pcie lanes allowing it to run more than just the 2 x8 connections the z series mobos can.

Edited February 2, 2018 by Brooksie359
Autocorrect :(

[VolkA]

Just now, Brooksie359 said:

It is with all z series mobos. They have an x99 mobo with a gpu that has more pcie lanes allowing it to run more than just the 2 x8 connections the z series mobos can.

Ohhh. Okok. I guess I have not really update myself for a few years. Time for more researches and reading I guess.

[Brooksie359]

Just now, VolkA said:

Ohhh. Okok. I guess I have not really update myself for a few years. Time for more researches and reading I guess.

Also when I said gpu it is meant to be cpu. My damn autocorrect changes it for some dumb reason.

[Ace McPlane]

7 hours ago, Jewish-Man said:

Hello. I recently got a new laptop to use for school that is also pretty well equipped for gaming. As I was using this laptop, I noticed something strange. I was getting better performance in games on my laptop rather than my desktop. How could this be? My desktop is more powerful in every way.

 

Some research into my bios has revealed that my GPU's are only using 8 PCI-E lanes a piece when I have 40 total available. I am using an m.2 drive as my os drive as well. With all of these PCI-E devices together I should only be running 36 lanes actively (16+16+4=36). After spending awhile just browsing through the BIOS, I was unable to find anything that appeared to allow me to change the number of PCI-E lanes that each slot was using. Am I just missing something?

 

I know this isn't my only issue causing performance issues most likely, but it is definitely an issue. 

 

My system specs are included in the spoiler. I have confirmed that I am using the latest version of the BIOS available for my motherboard dated 18JULY2016.

 

Thanks for any help in advance!

 

  Hide contents

• CPU
  Intel i7 6850k @ 3.9 GHz
• Motherboard
  MSI SLI Plus X99S
• RAM
  Corsair Vengeance LPX 32GB (2x16GB) DDR4 2400
• GPU
  Gigabyte G1 gaming GTX 1080 x2 SLI
• Case
  Coolermaster HAF X
• Storage
  Samsung 950 pro 512GB
• PSU
  EVGA SuperNOVA 850 T2
• Display(s)
  Asus PG278Q @ 2560X1440 144Hz Via Display Port, Asus VG248QE @ 1920x1080 144Hz Via DL-DVI
• Cooling
  Cooler Master Hyper 212 EVO
• Keyboard
  CORSAIR K70 RGB RAPIDFIRE Mechanical Gaming Keyboard
• Mouse
  Logitech G900
• Sound
  STEELSERIES Siberia 800
• Operating System
  Windows 10 Pro 64 bit

2

 

Well, with my Asus Hero VII, it disables certain lanes and limits the x16 lane to x8 when certain things are plugged into certain slots. The M.2. drive slot is the biggest culprit I know of for this. This doesn't make sense in your case though. In my case, it's because I'm on the z97 platform and my CPU only actually has 16 PCIe lanes. With your setup, it would make no sense for it to start disabling slots and lanes.. There is a bios setting for this though. I'm not sure if your MSI board will have it though. Asus boards just have every option you can think of. 

 

If you do have the option though,

It'd likely be under the advanced options in your bios

and it would be called something like PCIe configuration or PCIe mode.

something like that.

 

I think though, in order to get that to work in x16 mode you're going to have to start pulling cards out to see what's causing the slot to run in x8.