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External GPU on Linux review

Written by Solène, on 01 September 2021.
Tags: #linux #gentoo #games #egpu

Comments on Fediverse/Mastodon

1. Introduction §

I like playing video games, and most games I play require a GPU that is more powerful than the integrated graphic chipset that can be found in laptop or computers. I recently found that external graphic card were a thing, and fortunately I had a few spare old graphic card for trying.

The hardware is called an eGPU (for external GPU) and are connected to the computer using a thunderbolt link. Because I buy most of my hardware second hand now, I've been able to find a Razer Core X eGPU (the simple core X and not the core X Chroma which provides USB and RJ45 connectivity on the case through thunderbolt), exactly what I was looking for. Basically, it's an external case with a PSU inside and a rack, pull out the rack and insert the graphic card, and you are done. Obviously, it works fine on Windows or Mac but it can be tricky on Linux.

Razer core X product

Attempt to make a picture of my eGPU with an nvidia 1060 in it
Attempt to make a picture of my eGPU with an nvidia 1060 in it

2. My setup §

I'm using a Lenovo T470 with an i5 CPU. When I want to use the eGPU, I connect the thunderbolt wire and keyboard / mouse (which I connect through an USB KVM to switch those from a computer to another). The thunderbolt port also provide power to the laptop which is good to know.

3. How does it work? §

There are two ways to use this device, the display can be connected to the eGPU itself or the rendering could be done on the laptop (let's say we only target laptops here) using the eGPU as a discrete card (only rendering, without display). Both modes have pros and cons.

  • External display Pros: best performance, allow many displays to be used
  • External display Cons: require a screen
  • Discrete mode Pros: no extra wire, no different setup when using the laptop without the eGPU
  • Discrete mode Cons: performance penalty, support doesn't work well on Linux

The performance penalty comes from the fact the thunderbolt bandwidth is limited, and if you want to display on your screen you need to receive the data back which will reduce the bandwidth allowed for rendering. A penalty of at least 20% should be expected in normal mode, and around 40% in discrete mode. This is not really fun but for a nice boost with an old graphic card this is still nice.

eGPU on Linux with a Razer core X Chroma

eGPU benchmarks

4. Configuration (NVIDIA) §

It's quite simple now in 2023 (blog update), the first step is to install nvidia-drivers.

4.1. Discrete mode §

- Add your user to the video group (at least on Gentoo)

- No /etc/X11/xorg.conf file is required

- The graphical card should appear in nvidia-settings under a "PRIME" menu

- Use prime-run as a prefix to run commands, the discrete mode is simply enabled by environment variables. If prime-run isn't a thing in your distribution, create a script nvidia-offload like explained in the NixOS wiki

NixOS wiki: Nvidia - offload mode

If you want to run Flatpak programs with the discrete GPU, you will need to set all the environment variables in the flatpak program environment. You can't just set them in your shell and run flatpak from there because of the sandboxing.

4.2. External display §

- Run nvidia-xconfig to create a /etc/X11/xorg.conf file that uses the Nvidia card as the main display

4.3. Both mode §

I ended figuring a xorg.conf allowing me to keep the same file with and without the eGPU, and to use the discrete and external display at the same time. The funniest part is if you run a program on the nvidia screen and move it back to the laptop screen, the eGPU continues to render it.

It's by far the most convenient configuration as you have nothing to tweak, and you can use laptop + eGPU displays.

Section "ServerLayout"
    Identifier "layout"
    Screen 0 "intel"
    Inactive "nvidia"
    Option "AllowNVIDIAGPUScreens"

Section "Device"
    Identifier "intel"
    Driver "modesetting"
    BusID  "PCI:0:2:0"

Section "Screen"
    Identifier "intel"
    Device "intel"

Section "Device"
    Identifier "nvidia"
    Driver "nvidia"
    BusID  "PCI:10:0:0"
    Option "AllowExternalGpus" "True"

Section "Screen"
    Identifier "nvidia"
    Device "nvidia"

4.4. Switching between modes §

If you want to switch from one to the other, you need to exit all X servers first. Booting with a xorg.conf for Nvidia while not having a Nvidia card plugged in will prevent X to start, which is annoying.

The program egpu-switch can help in that regard, but it can't choose between discrete or external display mode, you will need to decide which mode you prefer when the card is plugged by providing the according xorg.conf file.

egpu-switcher GitHub project page

5. What to expect of it on Linux? §

I've been using this on Gentoo only so far, but I had a previous experience with a pretty similar setup a few years ago with a laptop with a discrete nvidia card (called Optimus at that time), and the GPU was only usable as a discrete GPU and it was a mess at that time.

As for the eGPU, in external mode it works fine using the nvidia driver, I needed an xorg.conf file to tell to use the nvidia driver, then the display would be fine and 3D would work perfectly as if I was using a "real" card on a computer. I can play high demanding games such as Control, Death Stranding or other games using my Thinkpad Laptop when docked, this is really nice!

The setup is a bit weird though, if I want to undock, I need to prepare the new xorg.conf file and stop X, disconnect the eGPU and restart the display manager to login. Not very easy. I've been able to script it using a simple script at boot that will detect the Nvidia GPU and choose the correct xorg.conf file just before starting the display manager, it works quite fine and makes life easier.

6. Video games? §

I've been playing Steam video games, it works absolutely perfectly due to their work on Proton to make Windows games running. GOG games works fine too, I use Lutris games library manager to handle them and it works so far.

Now, there is the tricky discrete mode. On linux, the bumblebee project allows rendering a program in a virtual display to benefit from the 3D acceleration and then show it on another device, this work was done for Optimus hardware hence the bumblebee name (related to Transfomers lore). Steam doesn't like bumblebee at all and won't start game, this is a known bug, Steam is bad at managing multiple GPUs. I've not been able to display anything using bumblebee.

On the other hand, native Linux GOG games were working fine using bumblebee, however I don't own much high demanding Linux games so I've not been able to see if the performance hit was hard. Windows GOG games wouldn't run, partially because the DXVK (directX to vulkan) Wine rendering can't be used because bumblebee doesn't allow using Vulkan graphical API and error messages were unhelpful. I have literally lost two days of my life trying to achieve something useful with the discrete GPU mode but nothing came out of it, except native Linux games.

Playing Control on Gentoo (windowed for the screen)
Playing Control on Gentoo (windowed for the screen)

7. Why using an eGPU? §

Laptops are very limited in their upgrade capabilities, adding a GPU could avoid someone to own a "gaming" tower PC and a good laptop. The GPU is 100% replaceable because the case offers a pci express port and a standard PSU (which can be replaced too!). The EGPU could be shared among a few users in a home too. This is a nice way to recycling old GPUs for a nice graphic boost to play everything that is more than 5 years old (and that's a bunch of good games!). I think using a top notch GPU in this would be a waste though.

8. Conclusion §

I'm pretty happy with the experience so far, now I can play my favorites games on Linux using the same computer I like to use all the day. While the experience is not as plug and play than it is on Windows, it is solid and stable.

9. Troubleshoot §

Some reminders when something is wrong.

9.1. OpenSUSE setup §

This distribution ships with a tool "prime-select" which is very convenient, you can pick which driver you want to enable first, or if you want to do discrete rendering.

9.2. No sound §

An udev rule is certainly blocking the audio device for some reasons... On a system, I found the file "/lib/udev/rules.d/90-nvidia-udev-pm-G05.rules" with a comment about disabling audio devices, commenting it solves the problem.