5d07e69461
Create an environment variable to allow to set the copy mode. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4251>
67 lines
2.5 KiB
Markdown
67 lines
2.5 KiB
Markdown
# Multi-GPU
|
|
|
|
## Selecting the primary GPU
|
|
|
|
When multiple GPUs are present in the same system, Mutter applies a series of
|
|
rules to select one of them as primary. However, it is possible to manually
|
|
select a different GPU by using a udev rule.
|
|
|
|
To illustrate it with an example, I'm going to make the NVIDIA GPU in my system
|
|
to be selected as the primary GPU.
|
|
|
|
Start by finding the vendor and device IDs of the target GPU:
|
|
|
|
```bash
|
|
$ lspci -nn
|
|
[...]
|
|
24:00.0 VGA compatible controller [0300]: NVIDIA Corporation AD107 [GeForce RTX 4060] [10de:2882] (rev a1)
|
|
```
|
|
|
|
In this case, we are looking for the vendor ID (10de) and the product (2882).
|
|
|
|
Next, create rule to set the desired GPU as primary. Make sure to replace the
|
|
vendor and device IDs:
|
|
|
|
```bash
|
|
$ cat /etc/udev/rules.d/61-mutter-preferred-primary-gpu.rules
|
|
SUBSYSTEM=="drm", ENV{DEVTYPE}=="drm_minor", ENV{DEVNAME}=="/dev/dri/card[0-9]", SUBSYSTEMS=="pci", ATTRS{vendor}=="0x10de", ATTRS{device}=="0x2882", TAG+="mutter-device-preferred-primary"
|
|
```
|
|
|
|
Finally, restart and check that the desired GPU was selected:
|
|
|
|
```bash
|
|
$ journalctl -b0 /usr/bin/gnome-shell
|
|
[...]
|
|
Device '/dev/dri/card1' prefers shadow buffer
|
|
Added device '/dev/dri/card1' (nouveau) using non-atomic mode setting.
|
|
Device '/dev/dri/card2' prefers shadow buffer
|
|
Added device '/dev/dri/card2' (amdgpu) using atomic mode setting.
|
|
Created gbm renderer for '/dev/dri/card1'
|
|
Created gbm renderer for '/dev/dri/card2'
|
|
GPU /dev/dri/card1 selected primary given udev rule
|
|
```
|
|
|
|
## Copy modes
|
|
|
|
Mutter composites the buffer to be displayed on all displays on the primary GPU,
|
|
regardless of which GPU the display is connected to.
|
|
|
|
Therefore, when a display is connected to a secondary GPU, the contents to be
|
|
displayed on that display need to be copied from the primary GPU to the
|
|
secondary GPU.
|
|
|
|
There are 3 copy modes available:
|
|
|
|
- Secondary GPU copy mode: The copy is performed by the secondary GPU. This is
|
|
the default copy mode.
|
|
- Zero-copy mode: The primary GPU exports a framebuffer and the secondary GPU
|
|
imports it. This mode is tried if the secondary GPU copy mode fails.
|
|
- Primary GPU copy mode: The primary GPU copies its contents to a dumb buffer
|
|
and the secondary GPU scan-outs from it. First, the GPU is used to perform
|
|
the copy and, if it fails, the copy is perform by the CPU. This mode is used
|
|
if the zero-copy mode fails.
|
|
|
|
For debug purposes, it is possible to force the copy mode by setting the
|
|
environment variable `MUTTER_DEBUG_MULTI_GPU_FORCE_COPY_MODE` to `zero-copy`,
|
|
`primary-gpu-gpu` or `primary-gpu-cpu`.
|