[Edit: htop gave misleading metrics] Blender-hip doesn’t use gpu for rendering frames

Help
1

Background:

I have blender-hip installed since I have an rx 7600 gpu on my server:

  • CPU: AMD Ryzen 7 5700X (16) @ 4.66 GHz
  • GPU: AMD Radeon RX 7600 [Discrete]

My system config is this: https://codeberg.org/BlastboomStrice/dotfiles/src/.config/nixos-config/hosts/nixos-base/configuration.nix

  • I have enabled these:
hardware.graphics = {
  enable = true;
  enable32Bit = true;
};
hardware.amdgpu.opencl.enable = true;
My system metadata is here
  • system: "x86_64-linux"
  • host os: Linux 6.12.63, NixOS, 26.05 (Yarara), 26.05.20251228.c0b0e0f
  • multi-user?: yes
  • sandbox: yes
  • version: nix-env (Lix, like Nix) 2.94.0 System type: x86_64-linux Additional system types: i686-linux, x86_64-v1-linux, x86_64-v2-linux, x86_64-v3-linux Features: gc, signed-caches System configuration file: /etc/nix/nix.conf User configuration files: /home/base/.config/nix/nix.conf:/home/base/.config/kdedefaults/nix/nix.conf:/etc/xdg/nix/nix.conf:/home/base/.nix-profile/etc/xdg/nix/nix.conf:/nix/profile/etc/xdg/nix/nix.conf:/home/base/.local/state/nix/profile/etc/xdg/nix/nix.conf:/etc/profiles/per-user/base/etc/xdg/nix/nix.conf:/nix/var/nix/profiles/default/etc/xdg/nix/nix.conf:/run/current-system/sw/etc/xdg/nix/nix.conf Store directory: /nix/store State directory: /nix/var/nix Data directory: /nix/store/azv639a070gjjjr2h0bld6kf30xxr65y-lix-2.94.0/share
  • nixpkgs: /nix/store/xzl5dhddgjxp2p18h5qpkhvlkp8128j1-source

In blender in:

  • Edit/Preferences/System:
    • I have chosen HIP
    • Enabled both RX7600 gpu and Ryzen 7 5700X
    • Did not enable HIP RT because it makes system crash when using Cycles with Gpu
    • Kept display graphics at OpenGL
  • In Render options:
    • I have chosen Cycles as Rendering Engine
    • I have chosen GPU Compute as Device
      • I have also tried using CPU
    • I have Denoise enabled only in Render
      • I also tried turning it off

Issue

Using htop to monitor both cpu and gpu usage, blender seems to use the gpu ONLY to display, not render.

  • Looking around an object in cycles the cpu usage stays at around 10% while gpu goes to around 20%. But as soon as I stop looking around and let the frame render, gpu usage drops to around 0% and the cpu stays at around 10% (that’s cause I see practically one thread goes to 100%).
  • When rendering the frame (by pressing F12) the cpu usage goes to around 100%, while gpu goes to 1% (probably to display the image).
  • During all these, htop reports 0.0% compute usage for the gpu, only gfx usage seems to change

Expected behaviour

Blender should use the gpu when rendering.

2

Checking gpu usage with lact apparently the gpu is used, so apparaently htop simply cannot read/display gpu compute usage. Closing this.