Home / ubuntu / Questions / 1506064
Accepted
popey
Asked: 2024-02-29 17:37:47 +0800 CST

Slow rendering. Which GPU is a desktop process running on?

  • 772

The question

Sometimes, applications feel like they're rendering slowly. I don't know which of the multiple GPUs is doing the work for that specific application. I would like to know which GPU is rendering a window or application. How do I find this out on a per-window or per-process basis?

System information

My desktop is running Ubuntu 23.10 on an Intel Skull Canyon NUC. It contains a weird CPU/GPU hybrid with Intel CPU and AMD GPU, on the same die.

alan@nuc:~$ lscpu | grep Model\ name
Model name:                         Intel(R) Core(TM) i7-8809G CPU @ 3.10GHz

alan@nuc:~$ lspci | grep AMD
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] 
  Polaris 22 XT [Radeon RX Vega M GH] (rev c0)

I also have an external GPU in a thunderbolt enclosure.

alan@nuc:~$ lspci | grep GeForce
40:00.0 VGA compatible controller: NVIDIA Corporation 
  TU102 [GeForce RTX 2080 Ti Rev. A] (rev a1)

I have three 1080p displays attached to the NVIDIA 2080 Ti. No displays are connected to the internal HDMI or DisplayPort connectors.

alan@nuc:~$ xrandr | grep "*"
   1920x1080     60.00*+  59.99    59.94    50.00  
   1920x1080     60.00*+  59.94    50.00    29.97  
   1920x1080     60.00*+  59.99    59.94    50.00

I am running the latest version of the Nvidia driver.

alan@nuc:~$ lsmod | grep ^nvidia\ 
nvidia              56811520  920 nvidia_uvm,nvidia_modeset
alan@nuc:~$ modinfo nvidia | grep ^version
version:        535.161.07
alan@nuc:~$ dpkg -l nvidia-driver* | grep ^ii
ii  nvidia-driver-535 535.161.07-0ubuntu0.23.10.1 amd64 
  NVIDIA driver metapackage

Edit: Adding this thanks to the answer below from Alistair Buxton. Interesting that the AMD GPU is the "Default" (which I suspect isn't what I want).

So the answer is I need to use switcheroo launch or launch using GNOME application launcher.

alan@nuc:~$ switcherooctl list
Device: 0
  Name:        Advanced Micro Devices, Inc. [AMD®/ATI] Polaris 22 XT [Radeon RX Vega M GH]
  Default:     yes
  Environment: DRI_PRIME=pci-0000_01_00_0

Device: 1
  Name:        NVIDIA Corporation TU102 [GeForce RTX 2080 Ti Rev. A]
  Default:     no
  Environment: __GLX_VENDOR_LIBRARY_NAME=nvidia __NV_PRIME_RENDER_OFFLOAD=1 __VK_LAYER_NV_optimus=NVIDIA_only

My workflow

I typically launch applications from their icon in the GNOME Shell launcher or from a shell script I manually run, which launches all my desktop applications on startup. However, there's also the option in the launcher to "Launch using Integrated Graphics Card".

For example, here's the standard Steam launcher icon menu:

Steam launcher menu

The problem

Sometimes, I feel like applications are rendering slowly.

Restating the question

I'd like to know how I know which GPU is in use by a process or window.

Happy to hear other opinions like:

  • You're seeing things
  • It's the thunderbolt which is slow

Not inclined to do any of these: :)

  • Use Wayland
  • Use the open source nouveau driver
  • Remove the NVidia GPU
drivers

1 Answers

  1. Best Answer

    Run switcherooctl list and you will see output like this for each GPU:

    Device: 0
  Name:        NVIDIA Corporation TU104 [GeForce RTX 2070 SUPER]
  Default:     yes
  Environment: __GLX_VENDOR_LIBRARY_NAME=nvidia __NV_PRIME_RENDER_OFFLOAD=1 __VK_LAYER_NV_optimus=NVIDIA_only

    Note the environment section. Gnome Shell launches programs with switcherooctl launch, which just inserts those variables into the program's environment. So when you want to determine which GPU a program is running on, check /proc/$pid/environ for environment variables matching one of the devices in the list.

    Edit to add: my understanding is that Gnome only uses switcheroo if you explicitly choose one of the "integrated" or "discrete" options. Otherwise it just runs the program normally. You won't see either set of variables in the environment, and absent any other config, the program will be running on whichever GPU your monitor is connected to.

    But do note I don't use either Gnome or a dual GPU set up so I could be wrong about this.

    You can verify that switcheroo launch works for a particular card by using it to launch glxgears -info and checking the value of GLX_RENDERER at the top of the output.

    • 0