[SOLVED] What issues may a Multi-GPU Arch system encounter?

sage-etcher · 2024-12-19 20:48:44

I am looking to multiboot Arch and NetBSD, but the latter does not support most modern GPUs, additionally, if it cannot find a card it falls back to software rendering (2). To work past this, I am looking to install 2 graphics cards, a Radeon RX 7800 XT for linux/windows gaming and a much older Radeon HD 5450 (1) for NetBSD dev environment.

Ignoring the NetBSD and Windows sides of things, what issues would be likely to encounter while running Arch?

I believe DRI_PRIME can be used to specify which card to use for acceleration (3), so that should handle both cards being able to share the same Monitor. If I recall correctly, Xorg allows you to specify which GPU to use for each monitor which should be helpful.
Are there any other issues that may be encountered using such a configuration?
With DRI_PRIME set to the RX7800XT, could the existence of the slower card impact performance?
If it were to cause noticeable performance issues, as a worst case scenario, could the 5450 be completely disabled within Arch?

Primarily I'm looking for a "what is to be expected" of such a configuration. I've never touched multi-GPU configurations and am not sure what, if any, challenges such entails.

A few sources noted earlier:
1. Radeon HD 5450 choice GPU for NetBSD: https://www.reddit.com/r/NetBSD/comment … r_targets/
2. Software Rendering (llvmpipe) on NetBSD: https://wiki.netbsd.org/laptops/
3. Multi-GPU (AMD and NVIDIA) in Arch: https://bbs.archlinux.org/viewtopic.php?id=285512

EDIT: fixed typo, 5450 not 5420
EDIT 2: RX not FX for gpu!

Last edited by sage-etcher (2024-12-23 14:58:06)

seth · 2024-12-19 23:39:17

For dual booting make sure to see the 3rd link below. Mandatory.
Disable it (it's NOT the BIOS setting!) and reboot windows and linux twice for voodo reasons.
Also check the entire article.

As for the GPUs, see https://wiki.archlinux.org/title/PCI_pa … h_via_OVMF
You can either pass one of them into a VM or hide it via the pci-stub driver.

both cards being able to share the same Monitor. If I recall correctly, Xorg allows you to specify which GPU to use for each monitor

So how many monitors do you plan to have?

If you feed both GPUs into the same monitor at the same time (and switch there) all monitor considerations are pretty much irrelevant - you make sure to use the desired GPU (either by completely hiding one or telling the display server - X11 or wayland - which one to use) and that's it.

If you have one monitor and attach it to one GPU and you're not too excited about swapping the plugs, you'll need render offloading which is standard for hybrid systems (notebooks) but not guaranteed to work with random GPUs off the shelf.
However: that's anything but an optimal solution, because copying the framebuffer will cause overhead and there's a good chance that vsync won't work (properly)

If you just want to jam 2 GPUs into the system and attach a monitor to each of them - and you can find a spare set of keyboard/mouse, you can run two sessions in parallel on the same system.
(Even w/ a single set of input devices you can run two independent X11 servers on the GPU w/o any issue, combining them w/o render offloading requires the legacy xinerama extension which conflicts w/ xrandr and since a lot of software silently expects xrandr to be available, that will get you into trouble)

cryptearth · 2024-12-20 00:53:04

NetBSD 10.1, released on December 16, 2024 - I doubt that this will issues with something modern like a RX 7800 XT (AMD FX was a CPU series - not a GPU one)

sage-etcher · 2024-12-20 01:46:08

seth wrote:

For dual booting make sure to see the 3rd link below. Mandatory.
Disable it (it's NOT the BIOS setting!) and reboot windows and linux twice for voodo reasons.
Also check the entire article.
As for the GPUs, see https://wiki.archlinux.org/title/PCI_pa … h_via_OVMF
You can either pass one of them into a VM or hide it via the pci-stub driver.

No worries, I've dual booted windows and linux before! however I'm looking to tri-boot with NetBSD, not run it in a VM.

seth wrote:

So how many monitors do you plan to have?
If you feed both GPUs into the same monitor at the same time (and switch there) all monitor considerations are pretty much irrelevant - you make sure to use the desired GPU (either by completely hiding one or telling the display server - X11 or wayland - which one to use) and that's it.
If you have one monitor and attach it to one GPU and you're not too excited about swapping the plugs, you'll need render offloading which is standard for hybrid systems (notebooks) but not guaranteed to work with random GPUs off the shelf.
However: that's anything but an optimal solution, because copying the framebuffer will cause overhead and there's a good chance that vsync won't work (properly)

Currently I only have the 1 monitor, however I plan on adding a second eventually.
I think i will try connecting both to the monitor, and leave the swapping to it instead, thank you! ^^
Oml the framebuffer needing coppied didn't once cross my mind, yeah that is not ideal! oh no!

cryptearth wrote:

NetBSD 10.1, released on December 16, 2024 - I doubt that this will issues with something modern like a RX 7800 XT

Yeah you would think so, but unfortunately I dont believe they do yet. I cant find anything official on support for dedicated cards, however their integrated support is severely outdated, and as recent as April 2024, Ive found threads of folks saying that their RX580 (2017 Release) isnt yet supported.

cryptearth wrote:

(AMD FX was a CPU series - not a GPU one)

ope! ill fix that! aaaa my apologies lmao! thank you!

Head_on_a_Stick · 2024-12-20 09:34:26

For the record NetBSD 10 uses the DRM stack from Linux 5.6 so the 7800XT won't be supported.

EDIT: OpenBSD 7.6 ported the Linux 6.6.52 drivers so that should work well.

Last edited by Head_on_a_Stick (2024-12-20 09:38:18)

seth · 2024-12-20 09:39:06

Currently I only have the 1 monitor, however I plan on adding a second eventually.
I think i will try connecting both to the monitor, and leave the swapping to it instead, thank you! ^^
Oml the framebuffer needing coppied didn't once cross my mind, yeah that is not ideal! oh no!

Just use one GPU (the more capable one) - nothing else makes much sense in this setup and you won't have any downsides from the second one just sitting there (provided it doesn't default to maximum power draw for no reason

sage-etcher · 2024-12-20 13:31:26

Head_on_a_Stick wrote:

For the record NetBSD 10 uses the DRM stack from Linux 5.6

This is verry helpful, thank you!!

Arch Linux

#1 2024-12-19 20:48:44

[SOLVED] What issues may a Multi-GPU Arch system encounter?

#2 2024-12-19 23:39:17

Re: [SOLVED] What issues may a Multi-GPU Arch system encounter?

#3 2024-12-20 00:53:04

Re: [SOLVED] What issues may a Multi-GPU Arch system encounter?

#4 2024-12-20 01:46:08

Re: [SOLVED] What issues may a Multi-GPU Arch system encounter?

#5 2024-12-20 09:34:26

Re: [SOLVED] What issues may a Multi-GPU Arch system encounter?

#6 2024-12-20 09:39:06

Re: [SOLVED] What issues may a Multi-GPU Arch system encounter?

#7 2024-12-20 13:31:26

Re: [SOLVED] What issues may a Multi-GPU Arch system encounter?

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