(Solved) PCIE Lane issues

[aasberry]

Issue, I have been running unraid for a while.  I expected some performance loss in my gaming vm 5-10% but the bottom end was a lot more extreme than that (~50%).  I finally got around to troubleshooting the issue and it seems to be coming down to PCIE lanes and configurations.  And I may be crazy, but it felt like this was worse after installing a new NVME drive.  My current setup:

 

Ryzen 1600

Asus b350-f Strix

PCIE x16 slot 1 - GT710 (Gets x8 in this slot)

PCIE x16 slot 2 - RX 480 (It was either 2.0 or 3.0 at x4)

Ram 16GB

 

VMs:

VM1 - Windows 10 Blue iris

VM2 - Windows 10 Gaming

 

 

The RX480 running at x4 PCIE lanes seems to have quite the impact on the bottom end of my frame rates.  So, I need a solution and I have not found a decent answer yet.

 

Option 1:  If I could boot to unraid using the GT 710 in the second PCIE 16 slot this would solve my problems.  Idk how to do this not have I found good information on it yet if you know plz help.

 

Option 2: Throw money at it?  Get a x470 or x570 board instead that can actually run x8 +x8 I think that would help a good bit.  A good board recommendation that's not too expensive would be greatly appreciated!

 

If anyone has a better option I am definitely open to ideas!  I tried running unraid headless in the past and I had a lot of issues. But maybe I was just doing it wrong...

 

 

-Struggling Noob.

 

 

 

Solved: I was able to get things operating much more smoothly.  First off I had to remove CPU pinning.  I do not know why but this actually caused horrible stuttering.  Next I added another full cpu to the VM which really smoothed things out.   I thought the lanes were having more impact than then were.  Now I would say I am only losing about %10 off of my normal benchmark scores.  -  Thanks to everyone who helped!

 

Edited September 15, 2020 by aasberry

[Decto]

Just working on a simlar build but using workstation Xeon E5 board with lots of PCI-E flexibility.

Still having to comprimise in some areas.

 

PCI-E x4 should be Gen 3 in your second x16 slot, but that is likely a bottleneck for an RX480 as it caps the rate you can load textures into memory.

 

Not many boards allow you to choose VGA priority, you'll need to work through the advanced settings in the BIOS to see if there is a VGA priority or VGA PCI-E initialisation selection etc. Likely not, as mainly Gigabyte who enable this.

 

You may be able to use CSM, which is compataibility mode for non UEFI hardware / OS. 

Again you will need to hunt for this in the BIOS but it is documented in the manual - set to enable rather than Auto.

If you enable this, it should prioritise a GPU connected to the chipset at boot which would be your PCI-E X16_3 at the bottom of the board.

The GT710 would be quite happy with even a X1 lane and that should allow you access to the other two slots for GPU's.

 

The other two PCI-E X 16 slots are electrically connected to the CPU so should initialise later.

 

Failing that, GPU (VGA) BIOS passthrough. 

You either need to download an identical or compatable GPU BIOS or download the one from your card then pass this through on VM startup, there is a section for it in the VM creation tool. This should then allow you to pass through the primary GPU to an VM. 

 

Good luck 

 

 

 

 

 

 

 

 

[scorcho99]

The secondary slot is going to be a chipset driven pcie 4x 2.0 on that board. 50% performance loss still seems a bit extreme in that configuration but there would be a hit.

 

Regarding your option 1: Try to find an option to disable your CSM in the bios. On Ryzen at least, that seems to swap the primary boot GPU to chipset ports.

[mrjrp15]

You could try a bifurcating the x16 PCIE slot into multiple x8 slots. This will only work if the board supports bifurcation. I have been wanting to try on my Asrock b350 Fatality, since it does support this. However, it has some implications like case choice and additional power overhead. 

https://riser.maxcloudon.com/en/