GPU problems under linux

HI! I have a post about this same issue in the hardware forum but i think that might be the wrong place for it so im making one here. I need some help with gpus under linux. I intend to setup passthrough with a quadro k600 as the host gpu and a gtx 970 in the vm. The problem is that when i attempt to run my monitors of the quadro i get terrible lag. This doesn`t happen if it is the only gpu in the system. It only happens when both gpus are in. I also get different options for driver install in the driver menu when the quadro is the only gpu in the system.

here they are listed in lspcio

1b:00.0 VGA compatible controller: NVIDIA Corporation GK107GL [Quadro K600] (rev a1

1c:00.0 VGA compatible controller: NVIDIA Corporation GM204 [GeForce GTX 970] (rev a1)

this is a fresh install of ubuntu 18.04 if that is important.

help would be much appreciated

make sure they’re settled right in their slots. alot of bioses looks through their GPUs available by checking the first slot e.g. the one highest slotted on your mounted MOBO, then downwards(first slot even superseeds the CPU graphics alot of times).
It drowe me crazy before i figured it out, because i could litterally do a perfect setup for passthrough and for some reason my Os went all retarded when i passed my gaming GPU into a VM(offcourse this was the one slotted top).
I’d suggest making sure your gaming gpu is slotted in mmh your second/third slot, and then use a stub setup since nvidia drivers are “abit” sketchy, so by attaching the physical hardware to a stub you avoid the drivers doing some wierd thing in the background, since they’re both nvidia, since all it sees is nothing, before you release and passthrough.
Il’l admit it’s been a while since i tried it last but i doubt bioses have changed that much since early ubuntu 16.04.

Thanks for the reply. The problem is i cant put the gaming card in the bottom slot because it is too big. The thing is this is before even having passed anything through. Im really confused as to why the performance of the quadro would be different without the 970 in the case. It`s still in the same slot so the performance shouldnt be different right.

if the BIOS sees your 970 as it’s main GPU, so will linux, this is simply handed off to the OS.
I’d allmost wager you that if you moved your monitors connection to your other GPU, it’d still do all rendering on your “primary” GPU, and just pass through the rendered image to another GPU.
This is why you need to make sure your bios choose your quadro as your primary, then you can go all silly with your secondary GPU.
even worse if you try and passthrough your primary GPU, be ready for some emergency consoles and what not.

I see. Im gonna see if i can switch primary gpu somehow in bios.

Doesn`t seem like i can. Do you know if i can force X11 to run on the secondary card? because then i should be able to pass through the primary one right?

I have the exact same issues as you ghishnchips. I have the gpu I want to use for the passthrough in the pci slot nearest to the cpu and have the one I want to use solely for Ubuntu in the last slot near the edge of the motherboard. Having both gpus in the system while only outputting to the second gpu causes Ubuntu to freeze and eventually stop responding after login. Taking the first GPU out completely solves the problem. And exactly like you I cannot put my gaming graphics card in the other slot because I am using a matx mobo and a dual slot card cannot fit into that slot. I’ve been banging my head against the wall trying to figure this out and I’m glad I am not the only one having this problem. It also doesn’t seem that I have an option to choose my main gpu anywhere in my bios. It’s strange because if this were some kind of hardware problem like Lauritzen is suggesting I don’t understand why I can boot my Windows install and do the exact same thing but it works perfectly fine. Let me know if you ever find a solution.