It was great meeting (some of) you guys at NixCon!

Have you had a chance to look at the nix-community hydra situation connor (he/him) (UTC+2)?

the nix-community hydra situation

Is there a problem with it?

Hello!

I am trying to launch tests that rely on CUDA, following help from Gaétan Lepage yesterday, but I do not succeed.
My host is running nixpkgs 25.05, with a clone of nixpkgs/master in the current directory.

Any idea how to get this to run?

nix-build -I nixpkgs=. --arg config '{ allowUnfree = true; cudaSupport = true;}' -A python313Packages.triton.tests.axpy-cuda.gpuCheck
this derivation will be built:
  /nix/store/2m1zkm221qr6ziw2qkbds3r37r57f7xj-test-cuda.drv
building '/nix/store/2m1zkm221qr6ziw2qkbds3r37r57f7xj-test-cuda.drv'...
Traceback (most recent call last):
  File "/nix/store/biwmrywsnh5nvfxg13d319cx65956rvc-tester-cuda/bin/tester-cuda", line 38, in <module>
    x = torch.rand(size, device='cuda')
  File "/nix/store/419qp86g5l617y4pv5m0fgj04rhfnxrp-python3-3.13.6-env/lib/python3.13/site-packages/torch/cuda/__init__.py", line 412, in _lazy_init
    torch._C._cuda_init()
    ~~~~~~~~~~~~~~~~~~~^^
RuntimeError: Found no NVIDIA driver on your system. Please check that you have an NVIDIA GPU and installed a driver from http://www.nvidia.com/Download/index.aspx
error: builder for '/nix/store/2m1zkm221qr6ziw2qkbds3r37r57f7xj-test-cuda.drv' failed with exit code 1;
       last 7 log lines:
       > Traceback (most recent call last):
       >   File "/nix/store/biwmrywsnh5nvfxg13d319cx65956rvc-tester-cuda/bin/tester-cuda", line 38, in <module>
       >     x = torch.rand(size, device='cuda')
       >   File "/nix/store/419qp86g5l617y4pv5m0fgj04rhfnxrp-python3-3.13.6-env/lib/python3.13/site-packages/torch/cuda/__init__.py", line 412, in _lazy_init
       >     torch._C._cuda_init()
       >     ~~~~~~~~~~~~~~~~~~~^^
       > RuntimeError: Found no NVIDIA driver on your system. Please check that you have an NVIDIA GPU and installed a driver from http://www.nvidia.com/Download/index.aspx
       For full logs, run:
         nix log /nix/store/2m1zkm221qr6ziw2qkbds3r37r57f7xj-test-cuda.drv

 python
Python 3.12.11 (main, Jun  3 2025, 15:41:47) [GCC 14.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import torch
>>> torch.cuda.is_available()
True

nix-shell -I nixpkgs=. --arg config '{ allowUnfree = true; cudaSupport = true;}' -p python312Packages.torch

[nix-shell:~/Repos/hoh/nixpkgs]$ python
Python 3.12.11 (main, Jun  3 2025, 15:41:47) [GCC 14.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import torch
>>> torch.cuda.is_available()
True

Thanks connor (he/him) (UTC+2) .

I can now launch the triton test.

However, when attempting to launch tests on the unstloth library, nix builds Torch for Python313 instead of Python 312.
Torch is not supported on Python 3.13 yet - it still attempts to build however which confuses me.

diff --git a/pkgs/development/python-modules/unsloth/default.nix b/pkgs/development/python-modules/unsloth/default.nix
index 73f94721b5e0..e6473c3bfa1d 100644
--- a/pkgs/development/python-modules/unsloth/default.nix
+++ b/pkgs/development/python-modules/unsloth/default.nix
@@ -27,6 +27,9 @@
   hf-transfer,
   diffusers,
   torchvision,
+
+  # tests
+  cudaPackages,
 }:
 
 buildPythonPackage rec {
@@ -85,6 +88,19 @@ buildPythonPackage rec {
   # NotImplementedError: Unsloth: No NVIDIA GPU found? Unsloth currently only supports GPUs!
   dontUsePythonImportsCheck = true;
 
+  passthru.tests = {
+    import-cuda = cudaPackages.writeGpuTestPython
+      {
+        libraries = ps: [
+          ps.torch
+        ];
+      }
+      ''
+        import unsloth
+        unsloth.test()
+      '';
+  };
+
   meta = {
     description = "Finetune Llama 3.3, DeepSeek-R1 & Reasoning LLMs 2x faster with 70% less memory";
     homepage = "https://github.com/unslothai/unsloth";

nix-build -I nixpkgs=. --arg config '{ allowUnfree = true; cudaSupport = true;}' -A python312Packages.unsloth.tests.import-cuda

I managed to launch a test on my package with CUDA enabled, but I get an issue from triton not finding a C compiler. Does that ring a bell to someone ?

RuntimeError: Failed to find C compiler. Please specify via CC environment variable or set triton.knobs.build.impl.

I share my work in progress in a draft PR here: https://github.com/NixOS/nixpkgs/pull/441728