Set version to 0.4.4 (#73)

* Add `has_kernel` function

This function checks whether a kernel build exists for the current
environment (Torch version and compute framework).

* Test kernel repo that only contains Torch 2.4

.github/workflows/lint.yml

@@ -0,0 +1,10 @@
+name: Lints
+on: [push, pull_request]
+jobs:
+  lint:
+    name: Run lints
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run ruff
+        uses: astral-sh/ruff-action@v3

.github/workflows/test.yml

@@ -1,4 +1,4 @@
-name: Test hf-kernels
+name: Test kernels
 
 on:
   push:
@@ -26,6 +26,9 @@ jobs:
         python-version: ["3.10", "3.12"]
         torch-version: ["2.5.1", "2.6.0"]
 
+    env:
+      UV_PYTHON_PREFERENCE: only-managed
+
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -41,5 +44,16 @@ jobs:
       - name: Install the project
         run: uv sync --all-extras --dev
 
+      - name: Install setuptools for Triton-based test
+        run: uv pip install setuptools
+
+      - name: Check typing
+        run: uv run mypy src/kernels
+
       - name: Run tests
         run: uv run pytest tests
+
+      - name: Import check without torch
+        run: |
+          uv pip uninstall torch
+          python -c "import kernels"

LICENSE

@@ -0,0 +1,201 @@
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README.md

@@ -1,11 +1,42 @@
-# hf-kernels
+# kernels
 
-Make sure you have `torch==2.5.1+cu124` installed.
+<div align="center">
+<img src="https://github.com/user-attachments/assets/64a652f3-0cd3-4829-b3c1-df13f7933569" width="450" height="450" alt="kernel-builder logo">
+<p align="center">
+    <a href="https://pypi.org/project/kernels"><img alt="PyPI - Version" src="https://img.shields.io/pypi/v/kernels"></a>
+    <a href="https://github.com/huggingface/kernels/tags"><img alt="GitHub tag" src="https://img.shields.io/github/v/tag/huggingface/kernels"></a>
+    <a href="https://github.com/huggingface/kernels/actions/workflows/docker-build-push.yaml"><img alt="Test kernels" src="https://img.shields.io/github/actions/workflow/status/huggingface/kernels/test.yml?label=test"></a>
+  
+</p>
+</div>
+<hr/>
+
+The Kernel Hub allows Python libraries and applications to load compute
+kernels directly from the [Hub](https://hf.co/). To support this kind
+of dynamic loading, Hub kernels differ from traditional Python kernel
+packages in that they are made to be:
+
+- Portable: a kernel can be loaded from paths outside `PYTHONPATH`.
+- Unique: multiple versions of the same kernel can be loaded in the
+  same Python process.
+- Compatible: kernels must support all recent versions of Python and
+  the different PyTorch build configurations (various CUDA versions
+  and C++ ABIs). Furthermore, older C library versions must be supported.
+
+## 🚀 Quick Start
+
+Install the `kernels` package with `pip` (requires `torch>=2.5` and CUDA):
+
+```bash
+pip install kernels
+```
+
+Here is how you would use the [activation](https://huggingface.co/kernels-community/activation) kernels from the Hugging Face Hub:
 
 ```python
 import torch
 
-from hf_kernels import get_kernel
+from kernels import get_kernel
 
 # Download optimized kernels from the Hugging Face hub
 activation = get_kernel("kernels-community/activation")
@@ -20,57 +51,14 @@ activation.gelu_fast(y, x)
 print(y)
 ```
 
-## Docker Reference
+You can [search for kernels](https://huggingface.co/models?other=kernel) on
+the Hub.
 
-build and run the reference [examples/basic.py](examples/basic.py) in a Docker container with the following commands:
+## 📚 Documentation
 
-```bash
-docker build --platform linux/amd64 -t kernels-reference -f docker/Dockerfile.reference .
-docker run --gpus all -it --rm -e HF_TOKEN=$HF_TOKEN kernels-reference
-```
-
-## Locking kernel versions
-
-Projects that use `setuptools` can lock the kernel versions that should be
-used. First specify the accepted versions in `pyproject.toml` and make
-sure that `hf-kernels` is a build dependency:
-
-```toml
-[build-system]
-requires = ["hf-kernels", "setuptools"]
-build-backend = "setuptools.build_meta"
-
-[tool.kernels.dependencies]
-"kernels-community/activation" = ">=0.0.1"
-```
-
-Then run `hf-kernel lock .` in the project directory. This generates a `kernels.lock` file with
-the locked revisions. The locked revision will be used when loading a kernel with
-`get_locked_kernel`:
-
-```python
-from hf_kernels import get_locked_kernel
-
-activation = get_locked_kernel("kernels-community/activation")
-```
-
-**Note:** the lock file is included in the package metadata, so it will only be visible
-to `hf-kernels` after doing an (editable or regular) installation of your project.
-
-## Pre-downloading locked kernels
-
-Locked kernels can be pre-downloaded by running `hf-kernel download .` in your
-project directory. This will download the kernels to your local Hugging Face
-Hub cache.
-
-The pre-downloaded kernels are used by the `get_locked_kernel` function.
-`get_locked_kernel` will download a kernel when it is not pre-downloaded. If you
-want kernel loading to error when a kernel is not pre-downloaded, you can use
-the `load_kernel` function instead:
-
-````python
-```python
-from hf_kernels import load_kernel
-
-activation = load_kernel("kernels-community/activation")
-````
+- [Using layers](docs/layers.md)
+- [Locking kernel versions](docs/locking.md)
+- [Environment variables](docs/env.md)
+- [Using kernels in a Docker container](docs/docker.md)
+- [Kernel requirements](docs/kernel-requirements.md)
+- [Writing kernels](https://github.com/huggingface/kernel-builder/blob/main/docs/writing-kernels.md) using [kernel-builder](https://github.com/huggingface/kernel-builder/)

docker/Dockerfile.reference

@@ -31,13 +31,13 @@ WORKDIR /app/kernel-test
 # install python depdencies
 RUN uv add torch==2.5.0 numpy
 
-# copy hf-kernels lib
-COPY src ./hf-kernels/src
-COPY pyproject.toml ./hf-kernels/pyproject.toml
-COPY README.md ./hf-kernels/README.md
+# copy kernels lib
+COPY src ./kernels/src
+COPY pyproject.toml ./kernels/pyproject.toml
+COPY README.md ./kernels/README.md
 
 # install library
-RUN uv pip install -e hf-kernels
+RUN uv pip install -e kernels
 
 # copy examples
 COPY examples ./examples
@@ -48,4 +48,4 @@ ENV NVIDIA_DRIVER_CAPABILITIES=compute,utility
 
 # command to run the script
 CMD ["uv", "run", "examples/basic.py"]
-# CMD ["ls", "hf-kernels"]
+# CMD ["ls", "kernels"]

docs/docker.md

@@ -0,0 +1,8 @@
+# Using kernels in a Docker container
+
+build and run the reference [examples/basic.py](examples/basic.py) in a Docker container with the following commands:
+
+```bash
+docker build --platform linux/amd64 -t kernels-reference -f docker/Dockerfile.reference .
+docker run --gpus all -it --rm -e HF_TOKEN=$HF_TOKEN kernels-reference
+```

docs/env.md

@@ -0,0 +1,10 @@
+# Environment variables
+
+## `KERNELS_CACHE`
+
+The directory to use as the local kernel cache. If not set, the cache
+of the `huggingface_hub` package is used.
+
+## `DISABLE_KERNEL_MAPPING`
+
+Disables kernel mappings for [`layers`](layers.md).

docs/kernel-requirements.md

@@ -0,0 +1,205 @@
+# Kernel requirements
+
+Kernels on the Hub must fulfill the requirements outlined on this page.
+You can use [kernel-builder](https://github.com/huggingface/kernel-builder/)
+to build conforming kernels.
+
+## Directory layout
+
+A kernel repository on the Hub must contain a `build` directory. This
+directory contains build variants of a kernel in the form of directories
+following the template
+`<framework><version>-cxx<abiver>-<cu><cudaver>-<arch>-<os>`.
+For example `build/torch26-cxx98-cu118-x86_64-linux`. The currently
+recommended build variants are:
+
+- `torch25-cxx11-cu118-x86_64-linux`
+- `torch25-cxx11-cu121-x86_64-linux`
+- `torch25-cxx11-cu124-x86_64-linux`
+- `torch25-cxx98-cu118-x86_64-linux`
+- `torch25-cxx98-cu121-x86_64-linux`
+- `torch25-cxx98-cu124-x86_64-linux`
+- `torch26-cxx11-cu118-x86_64-linux`
+- `torch26-cxx11-cu124-x86_64-linux`
+- `torch26-cxx11-cu126-x86_64-linux`
+- `torch26-cxx98-cu118-x86_64-linux`
+- `torch26-cxx98-cu124-x86_64-linux`
+- `torch26-cxx98-cu126-x86_64-linux`
+
+This list will be updated as new PyTorch versions are released. Kernels
+that are in pure Python (e.g. Triton kernels) only need to provide a
+single build variant:
+
+- `torch-universal`
+
+Each variant directory should contain a single directory with the same name
+as the repository (replacing `-` by `_`). For instance, kernels in the
+`kernels-community/activation` repository have a directories like
+`build/<variant>/activation`. This directory
+must be a Python package with an `__init__.py` file.
+
+## Versioning
+
+Kernels are versioned on the Hub using Git tags. Version tags must be of
+the form `v<major>.<minor>.<patch>`. Versions are used by [locking](./locking.md)
+to resolve the version constraints.
+
+## Native Python module
+
+Kernels will typically contain a native Python module with precompiled
+compute kernels and bindings. This module must fulfill the following
+requirements:
+
+- Use [ABI3/Limited API](https://docs.python.org/3/c-api/stable.html#stable-application-binary-interface)
+  for compatibility with Python 3.9 and later.
+- Compatible with [`manylinux_2_28`](https://github.com/pypa/manylinux?tab=readme-ov-file#manylinux_2_28-almalinux-8-based).
+  This means that the extension **must not** use symbols versions higher than:
+
+  - GLIBC 2.28
+  - GLIBCXX 3.4.24
+  - CXXABI 1.3.11
+  - GCC 7.0.0
+
+  These requirement can be checked with the ABI checker (see below).
+
+- No dynamic library dependencies outside:
+
+  - Torch;
+  - CUDA/ROCm libraries installed as dependencies of Torch.
+
+The manylinux_2_28 and Python ABI 3.9 version requirements can be checked with
+[`kernel-abi-check`](https://crates.io/crates/kernel-abi-check):
+
+```bash
+
+$ cargo install kernel-abi-check
+$ kernel-abi-check result/relu/_relu_e87e0ca_dirty.abi3.so
+🐍 Checking for compatibility with manylinux_2_28 and Python ABI version 3.9
+✅ No compatibility issues found
+```
+
+## Torch extension
+
+Torch native extension functions must be [registered](https://pytorch.org/tutorials/advanced/cpp_custom_ops.html#cpp-custom-ops-tutorial)
+in `torch.ops.<namespace>`. Since we allow loading of multiple versions of
+a module in the same Python process, `namespace` must be unique for each
+version of a kernel. Failing to do so will create clashes when different
+versions of the same kernel are loaded. Two suggested ways of doing this
+are:
+
+- Appending a truncated SHA-1 hash of the git commit that the kernel was
+  built from to the name of the extension.
+- Appending random material to the name of the extension.
+
+**Note:** we recommend against appending a version number or git tag.
+Version numbers are typically not bumped on each commit, so users
+might use two different commits that happen to have the same version
+number. Git tags are not stable, so they do not provide a good way
+of guaranteeing uniqueness of the namespace.
+
+## Layers
+
+A kernel can provide layers in addition to kernel functions. A layer from
+the Hub can replace the `forward` method of an existing layer for a certain
+device type. This makes it possible to provide more performant kernels for
+existing layers. See the [layers documentation](layers.md) for more information
+on how to use layers.
+
+### Writing layers
+
+To make the extension of layers safe, the layers must fulfill the following
+requirements:
+
+- The layers are subclasses of `torch.nn.Module`.
+- The layers are pure, meaning that they do not have their own state. This
+  means that:
+  - The layer must not define its own constructor.
+  - The layer must not use class variables.
+- No other methods must be defined than `forward`.
+- The `forward` method has a signature that is compatible with the
+  `forward` method that it is extending.
+
+The only exception to the _no class variables rule_ is addition of a
+`has_backward` class variable. This variable is used to indicate whether
+the layer has a backward pass implemented (`True` when absent).
+
+This is an example of a pure layer:
+
+```python
+class SiluAndMul(nn.Module):
+    # This layer does not implement backward.
+    has_backward: bool = False
+
+    def forward(self, x: torch.Tensor):
+        d = x.shape[-1] // 2
+        output_shape = x.shape[:-1] + (d,)
+        out = torch.empty(output_shape, dtype=x.dtype, device=x.device)
+        ops.silu_and_mul(out, x)
+        return out
+```
+
+For some layers, the `forward` method has to use state from the adopting class.
+In these cases, we recommend to use type annotations to indicate what member
+variables are expected. For instance:
+
+```python
+class LlamaRMSNorm(nn.Module):
+    weight: torch.Tensor
+    variance_epsilon: float
+
+    def forward(self, hidden_states: torch.Tensor) -> torch.Tensor:
+        return rms_norm_fn(
+            hidden_states,
+            self.weight,
+            bias=None,
+            residual=None,
+            eps=self.variance_epsilon,
+            dropout_p=0.0,
+            prenorm=False,
+            residual_in_fp32=False,
+        )
+```
+
+This layer expects the adopting layer to have `weight` and `variance_epsilon`
+member variables and uses them in the `forward` method.
+
+### Exporting layers
+
+To accommodate portable loading, `layers` must be defined in the main
+`__init__.py` file. For example:
+
+```python
+from . import layers
+
+__all__ = [
+  # ...
+  "layers"
+  # ...
+]
+```
+
+## Python requirements
+
+- Python code must be compatible with Python 3.9 and later.
+- All Python code imports from the kernel itself must be relative. So,
+  for instance if in the example kernel `example`,
+  `module_b` needs a function from `module_a`, import as:
+
+  ```python
+  from .module_a import foo
+  ```
+
+  **Never use:**
+
+  ```python
+  # DO NOT DO THIS!
+
+  from example.module_a import foo
+  ```
+
+  The latter would import from the module `example` that is in Python's
+  global module dict. However, since we allow loading multiple versions
+  of a module, we uniquely name the module.
+
+- Only modules from the Python standard library, Torch, or the kernel itself
+  can be imported.

docs/layers.md

@@ -0,0 +1,79 @@
+# Layers
+
+A kernel can provide layers in addition to kernel functions. A layer from
+the Hub can replace the `forward` method of an existing layer for a certain
+device type. This makes it possible to provide more performant kernels for
+existing layers.
+
+See [Kernel requirements](kernel-requirements.md) for more information the
+requirements of Hub layers.
+
+## Making a layer extensible with kernels from the hub
+
+### Using a decorator
+
+A layer can be made extensible with the `use_kernel_forward_from_hub`
+decorator. For example:
+
+```python
+@use_kernel_forward_from_hub("SiluAndMul")
+class SiluAndMul(nn.Module):
+    def forward(self, input: torch.Tensor) -> torch.Tensor:
+        d = input.shape[-1] // 2
+        return F.silu(input[..., :d]) * input[..., d:]
+```
+
+The decorator changes the layer, so that other implementations of the `forward`
+method can be registered using the name `SiluAndMul`.
+
+### External layers
+
+An existing layer that does not (yet) have the `use_kernel_forward_from_hub`
+decorator can be made extensible by by monkeypatching it using the `replace_kernel_forward_from_hub` function.
+
+```python
+from somelibrary import SiluAndMul
+
+replace_kernel_forward_from_hub(SiluAndMul, "SiluAndMul")
+register_kernel_mapping(kernel_layer_mapping)
+```
+
+The `register_kernel_mapping` call maps the name `SiluAndMul` to actual
+hub kernels. See the [Registering a hub kernel for a layer](#registering-a-hub-kernel-for-a-layer)
+section for more information.
+
+**Warning:** we strongly recommend using layers with a decorator, since
+it signifies that the maintainer intends to keep the `forward` signature
+compatible with layers from the hub.
+
+## Registering a hub kernel for a layer
+
+Once a layer is made extensible, users can register hub kernels for it
+by name using the `register_kernel_mapping` function. For example:
+
+```python
+kernel_layer_mapping = {
+    "SiluAndMul": {
+        "cuda": LayerRepository(
+            repo_id="kernels-community/activation",
+            layer_name="SiluAndMul",
+            revision="layers",
+        )
+    }
+}
+
+register_kernel_mapping(kernel_layer_mapping)
+```
+
+This will register the kernel mapping in the current context, which is
+normally global. It is recommended to scope the mapping to where it is
+used with the `use_kernel_mapping` context manager:
+
+```python
+with use_kernel_mapping(kernel_layer_mapping):
+    # Use the layer for which the mapping is applied.
+    ...
+```
+
+This ensures that the mapping is not active anymore outside the
+`with`-scope.

docs/locking.md

@@ -0,0 +1,44 @@
+# Locking kernel versions
+
+Projects that use `setuptools` can lock the kernel versions that should be
+used. First specify the accepted versions in `pyproject.toml` and make
+sure that `kernels` is a build dependency:
+
+```toml
+[build-system]
+requires = ["kernels", "setuptools"]
+build-backend = "setuptools.build_meta"
+
+[tool.kernels.dependencies]
+"kernels-community/activation" = ">=0.0.1"
+```
+
+Then run `kernel lock .` in the project directory. This generates a `kernels.lock` file with
+the locked revisions. The locked revision will be used when loading a kernel with
+`get_locked_kernel`:
+
+```python
+from kernels import get_locked_kernel
+
+activation = get_locked_kernel("kernels-community/activation")
+```
+
+**Note:** the lock file is included in the package metadata, so it will only be visible
+to `kernels` after doing an (editable or regular) installation of your project.
+
+## Pre-downloading locked kernels
+
+Locked kernels can be pre-downloaded by running `kernel download .` in your
+project directory. This will download the kernels to your local Hugging Face
+Hub cache.
+
+The pre-downloaded kernels are used by the `get_locked_kernel` function.
+`get_locked_kernel` will download a kernel when it is not pre-downloaded. If you
+want kernel loading to error when a kernel is not pre-downloaded, you can use
+the `load_kernel` function instead:
+
+```python
+from kernels import load_kernel
+
+activation = load_kernel("kernels-community/activation")
+```

examples/basic.py

@@ -1,6 +1,6 @@
 import torch
 
-from hf_kernels import get_kernel
+from kernels import get_kernel
 
 print("Starting examples/basic.py demo")
 

flake.lock

@@ -0,0 +1,134 @@
+{
+  "nodes": {
+    "flake-compat": {
+      "locked": {
+        "lastModified": 1733328505,
+        "narHash": "sha256-NeCCThCEP3eCl2l/+27kNNK7QrwZB1IJCrXfrbv5oqU=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "ff81ac966bb2cae68946d5ed5fc4994f96d0ffec",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "flake-utils_2": {
+      "inputs": {
+        "systems": "systems_2"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1737453259,
+        "narHash": "sha256-5LaFI9SQwCZmJDasMoYMdzNouWXNk3BvjKcO19tq1Rs=",
+        "owner": "danieldk",
+        "repo": "nixpkgs",
+        "rev": "e0372dbcfd19ddd783b7c3b3868f19322f83318e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "danieldk",
+        "ref": "outlines-v0.1.4-tgi",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": [
+          "tgi-nix",
+          "nixpkgs"
+        ],
+        "tgi-nix": "tgi-nix"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
+    "systems_2": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
+    "tgi-nix": {
+      "inputs": {
+        "flake-compat": "flake-compat",
+        "flake-utils": "flake-utils_2",
+        "nixpkgs": "nixpkgs"
+      },
+      "locked": {
+        "lastModified": 1741617161,
+        "narHash": "sha256-cwKYAsIVSLtoLbG48+oi3NkSrvuZRLYs8lkJmpDsTw0=",
+        "owner": "huggingface",
+        "repo": "text-generation-inference-nix",
+        "rev": "5946021ec6cb6aae18158a9dc27f893cfbab2925",
+        "type": "github"
+      },
+      "original": {
+        "owner": "huggingface",
+        "ref": "kernels-0.2.0",
+        "repo": "text-generation-inference-nix",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,54 @@
+{
+  inputs = {
+    tgi-nix.url = "github:huggingface/text-generation-inference-nix/kernels-0.2.0";
+    nixpkgs.follows = "tgi-nix/nixpkgs";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+      tgi-nix,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          inherit (tgi-nix.lib) config;
+          overlays = [
+            tgi-nix.overlays.default
+          ];
+        };
+      in
+      {
+        formatter = pkgs.nixfmt-rfc-style;
+        devShells = with pkgs; rec {
+          default = mkShell {
+            buildInputs =
+              [
+                black
+                mypy
+                pyright
+                ruff
+              ]
+              ++ (with python3.pkgs; [
+                huggingface-hub
+                pytest
+                pytest-benchmark
+                torch
+                venvShellHook
+              ]);
+
+            venvDir = "./.venv";
+
+            postVenvCreation = ''
+              unset SOURCE_DATE_EPOCH
+              ( python -m pip install --no-build-isolation --no-dependencies -e . )
+            '';
+          };
+        };
+      }
+    );
+}

pyproject.toml

@@ -1,20 +1,20 @@
 [project]
-name = "hf-kernels"
-version = "0.1.6"
-description = "Download cuda kernels"
+name = "kernels"
+version = "0.4.4"
+description = "Download compute kernels"
 authors = [
   { name = "OlivierDehaene", email = "olivier@huggingface.co" },
   { name = "Daniel de Kok", email = "daniel@huggingface.co" },
   { name = "David Holtz", email = "david@huggingface.co" },
   { name = "Nicolas Patry", email = "nicolas@huggingface.co" },
 ]
+license = { text = "Apache-2.0" }
 readme = "README.md"
 requires-python = ">= 3.9"
 dependencies = [
-  "huggingface-hub>=0.26.3",
-  "packaging>=24.2",
-  "tomli>=2.0.1; python_version<'3.11'",
-  "torch>=2.4",
+  "huggingface_hub>=0.26.0,<1.0",
+  "packaging>=20.0",
+  "tomli>=2.0; python_version<'3.11'",
 ]
 
 [build-system]
@@ -23,18 +23,46 @@ build-backend = "setuptools.build_meta"
 
 [dependency-groups]
 dev = [
+  "mypy == 1.14.1",
   "pytest >=8",
   # Whatever version is compatible with pytest.
   "pytest-benchmark",
+  "torch >=2.5",
 ]
 
+[project.optional-dependencies]
+torch = ["torch"]
+
 [project.scripts]
-hf-kernels = "hf_kernels.cli:main"
+kernels = "kernels.cli:main"
 
 [project.entry-points."egg_info.writers"]
-"hf-kernels.lock" = "hf_kernels.lockfile:write_egg_lockfile"
+"kernels.lock" = "kernels.lockfile:write_egg_lockfile"
 
-#[build-system]
-#requires = ["torch", "huggingface_hub", "numpy", "tomli;python_version<='3.10'"]
-#build-backend = "hf_kernels.build"
-#backend-path = ["src"]
+
+[tool.ruff]
+exclude = [
+  ".eggs",
+  ".git",
+  ".git-rewrite",
+  ".hg",
+  ".mypy_cache",
+  ".nox",
+  ".pants.d",
+  ".pytype",
+  ".ruff_cache",
+  ".svn",
+  ".tox",
+  ".venv",
+  ".venv*",
+  "__pypackages__",
+  "_build",
+  "build",
+  "dist",
+  "venv",
+]
+line-length = 119
+# Ignored rules:
+# "E501" -> line length violation
+lint.ignore = ["E501"]
+lint.select = ["E", "F", "I", "W"]

src/hf_kernels/__init__.py

@@ -1,3 +0,0 @@
-from hf_kernels.utils import get_kernel, install_kernel, load_kernel, get_locked_kernel
-
-__all__ = ["get_kernel", "get_locked_kernel", "load_kernel", "install_kernel"]

src/hf_kernels/build.py

@@ -1,144 +0,0 @@
-"""
-Python shims for the PEP 517 and PEP 660 build backend.
-
-Major imports in this module are required to be lazy:
-```
-$ hyperfine \
-     "/usr/bin/python3 -c \"print('hi')\"" \
-     "/usr/bin/python3 -c \"from subprocess import check_call; print('hi')\""
-Base: Time (mean ± σ):      11.0 ms ±   1.7 ms    [User: 8.5 ms, System: 2.5 ms]
-With import: Time (mean ± σ):      15.2 ms ±   2.0 ms    [User: 12.3 ms, System: 2.9 ms]
-Base 1.38 ± 0.28 times faster than with import
-```
-
-The same thing goes for the typing module, so we use Python 3.10 type annotations that
-don't require importing typing but then quote them so earlier Python version ignore
-them while IDEs and type checker can see through the quotes.
-"""
-
-from hf_kernels.compat import tomllib
-
-TYPE_CHECKING = False
-if TYPE_CHECKING:
-    from collections.abc import Mapping, Sequence  # noqa:I001
-    from typing import Any  # noqa:I001
-
-
-def warn_config_settings(config_settings: "Mapping[Any, Any] | None" = None) -> None:
-    import sys
-
-    if config_settings:
-        print("Warning: Config settings are not supported", file=sys.stderr)
-
-
-def call(
-    args: "Sequence[str]", config_settings: "Mapping[Any, Any] | None" = None
-) -> str:
-    """Invoke a uv subprocess and return the filename from stdout."""
-    import shutil
-    import subprocess
-    import sys
-
-    warn_config_settings(config_settings)
-    # Unlike `find_uv_bin`, this mechanism must work according to PEP 517
-    import os
-
-    cwd = os.getcwd()
-    filename = os.path.join(cwd, "pyproject.toml")
-    with open(filename, "rb") as f:
-        data = tomllib.load(f)
-
-    for kernel, _ in (
-        data.get("tool", {}).get("hf-kernels", {}).get("dependencies", {}).items()
-    ):
-        from hf_kernels.utils import install_kernel
-
-        install_kernel(kernel, revision="main")
-    uv_bin = shutil.which("uv")
-    if uv_bin is None:
-        raise RuntimeError("uv was not properly installed")
-    # Forward stderr, capture stdout for the filename
-    result = subprocess.run([uv_bin, *args], stdout=subprocess.PIPE)
-    if result.returncode != 0:
-        sys.exit(result.returncode)
-    # If there was extra stdout, forward it (there should not be extra stdout)
-    stdout = result.stdout.decode("utf-8").strip().splitlines(keepends=True)
-    sys.stdout.writelines(stdout[:-1])
-    # Fail explicitly instead of an irrelevant stacktrace
-    if not stdout:
-        print("uv subprocess did not return a filename on stdout", file=sys.stderr)
-        sys.exit(1)
-    return stdout[-1].strip()
-
-
-def build_sdist(
-    sdist_directory: str, config_settings: "Mapping[Any, Any] | None" = None
-) -> str:
-    """PEP 517 hook `build_sdist`."""
-    args = ["build-backend", "build-sdist", sdist_directory]
-    return call(args, config_settings)
-
-
-def build_wheel(
-    wheel_directory: str,
-    config_settings: "Mapping[Any, Any] | None" = None,
-    metadata_directory: "str | None" = None,
-) -> str:
-    """PEP 517 hook `build_wheel`."""
-    args = ["build-backend", "build-wheel", wheel_directory]
-    if metadata_directory:
-        args.extend(["--metadata-directory", metadata_directory])
-    return call(args, config_settings)
-
-
-def get_requires_for_build_sdist(
-    config_settings: "Mapping[Any, Any] | None" = None,
-) -> "Sequence[str]":
-    """PEP 517 hook `get_requires_for_build_sdist`."""
-    warn_config_settings(config_settings)
-    return []
-
-
-def get_requires_for_build_wheel(
-    config_settings: "Mapping[Any, Any] | None" = None,
-) -> "Sequence[str]":
-    """PEP 517 hook `get_requires_for_build_wheel`."""
-    warn_config_settings(config_settings)
-    return []
-
-
-def prepare_metadata_for_build_wheel(
-    metadata_directory: str, config_settings: "Mapping[Any, Any] | None" = None
-) -> str:
-    """PEP 517 hook `prepare_metadata_for_build_wheel`."""
-    args = ["build-backend", "prepare-metadata-for-build-wheel", metadata_directory]
-    return call(args, config_settings)
-
-
-def build_editable(
-    wheel_directory: str,
-    config_settings: "Mapping[Any, Any] | None" = None,
-    metadata_directory: "str | None" = None,
-) -> str:
-    """PEP 660 hook `build_editable`."""
-    args = ["build-backend", "build-editable", wheel_directory]
-
-    if metadata_directory:
-        args.extend(["--metadata-directory", metadata_directory])
-    return call(args, config_settings)
-
-
-def get_requires_for_build_editable(
-    config_settings: "Mapping[Any, Any] | None" = None,
-) -> "Sequence[str]":
-    """PEP 660 hook `get_requires_for_build_editable`."""
-    warn_config_settings(config_settings)
-    return []
-
-
-def prepare_metadata_for_build_editable(
-    metadata_directory: str, config_settings: "Mapping[Any, Any] | None" = None
-) -> str:
-    """PEP 660 hook `prepare_metadata_for_build_editable`."""
-    args = ["build-backend", "prepare-metadata-for-build-editable", metadata_directory]
-    return call(args, config_settings)

src/hf_kernels/utils.py

@@ -1,178 +0,0 @@
-import ctypes
-import importlib
-import importlib.metadata
-import inspect
-import json
-import os
-from pathlib import Path
-import platform
-import sys
-from importlib.metadata import Distribution
-from types import ModuleType
-from typing import List, Optional, Tuple
-
-from huggingface_hub import hf_hub_download, snapshot_download
-from packaging.version import parse
-
-from hf_kernels.compat import tomllib
-from hf_kernels.lockfile import KernelLock
-
-CACHE_DIR: Optional[str] = os.environ.get("HF_KERNELS_CACHE", None)
-
-
-def build_variant():
-    import torch
-
-    if torch.version.cuda is None:
-        raise AssertionError("This kernel requires CUDA to be installed. Torch was not compiled with CUDA enabled.")
-
-    torch_version = parse(torch.__version__)
-    cuda_version = parse(torch.version.cuda)
-    cxxabi = "cxx11" if torch.compiled_with_cxx11_abi() else "cxx98"
-    cpu = platform.machine()
-    os = platform.system().lower()
-
-    return f"torch{torch_version.major}{torch_version.minor}-{cxxabi}-cu{cuda_version.major}{cuda_version.minor}-{cpu}-{os}"
-
-
-def import_from_path(module_name: str, file_path):
-    # We cannot use the module name as-is, after adding it to `sys.modules`,
-    # it would also be used for other imports. So, we make a module name that
-    # depends on the path for it to be unique using the hex-encoded hash of
-    # the path.
-    path_hash = "{:x}".format(ctypes.c_size_t(hash(file_path)).value)
-    module_name = f"{module_name}_{path_hash}"
-    spec = importlib.util.spec_from_file_location(module_name, file_path)
-    module = importlib.util.module_from_spec(spec)
-    sys.modules[module_name] = module
-    spec.loader.exec_module(module)
-    return module
-
-
-def install_kernel(
-    repo_id: str, revision: str, local_files_only: bool = False
-) -> Tuple[str, str]:
-    """Download a kernel for the current environment to the cache."""
-    package_name = repo_id.split('/')[-1]
-    package_name = package_name.replace('-', '_')
-    repo_path = snapshot_download(
-        repo_id,
-        allow_patterns=f"build/{build_variant()}/*",
-        cache_dir=CACHE_DIR,
-        revision=revision,
-        local_files_only=local_files_only,
-    )
-
-    variant_path = f"{repo_path}/build/{build_variant()}"
-    module_init_path = f"{variant_path}/{package_name}/__init__.py"
-
-    if not os.path.exists(module_init_path):
-        raise FileNotFoundError(
-            f"Kernel `{repo_id}` at revision {revision} does not have build: {build_variant()}"
-        )
-
-    return package_name, variant_path
-
-
-def install_kernel_all_variants(
-    repo_id: str, revision: str, local_files_only: bool = False
-):
-    snapshot_download(
-        repo_id,
-        allow_patterns="build/*",
-        cache_dir=CACHE_DIR,
-        revision=revision,
-        local_files_only=local_files_only,
-    )
-
-
-def get_metadata(repo_id: str, revision: str, local_files_only: bool = False):
-    with open(
-        hf_hub_download(
-            repo_id,
-            "build.toml",
-            cache_dir=CACHE_DIR,
-            revision=revision,
-            local_files_only=local_files_only,
-        ),
-        "rb",
-    ) as f:
-        return tomllib.load(f)
-
-
-def get_kernel(repo_id: str, revision: str = "main"):
-    package_name, package_path = install_kernel(repo_id, revision=revision)
-    return import_from_path(package_name, f"{package_path}/{package_name}/__init__.py")
-
-
-def load_kernel(repo_id: str):
-    """Get a pre-downloaded, locked kernel."""
-    locked_sha = _get_caller_locked_kernel(repo_id)
-
-    if locked_sha is None:
-        raise ValueError(f"Kernel `{repo_id}` is not locked")
-
-    filename = hf_hub_download(
-        repo_id,
-        "build.toml",
-        cache_dir=CACHE_DIR,
-        local_files_only=True,
-        revision=locked_sha,
-    )
-    with open(filename, "rb") as f:
-        metadata = tomllib.load(f)
-    package_name = metadata["torch"]["name"]
-
-    repo_path = os.path.dirname(filename)
-    package_path = f"{repo_path}/build/{build_variant()}"
-    return import_from_path(package_name, f"{package_path}/{package_name}/__init__.py")
-
-
-def get_locked_kernel(repo_id: str, local_files_only: bool = False):
-    """Get a kernel using a lock file."""
-    locked_sha = _get_caller_locked_kernel(repo_id)
-
-    if locked_sha is None:
-        raise ValueError(f"Kernel `{repo_id}` is not locked")
-
-    package_name, package_path = install_kernel(
-        repo_id, locked_sha, local_files_only=local_files_only
-    )
-
-    return import_from_path(package_name, f"{package_path}/{package_name}/__init__.py")
-
-
-def _get_caller_locked_kernel(repo_id: str) -> Optional[str]:
-    for dist in _get_caller_distributions():
-        lock_json = dist.read_text("hf-kernels.lock")
-        if lock_json is not None:
-            for kernel_lock_json in json.loads(lock_json):
-                kernel_lock = KernelLock.from_json(kernel_lock_json)
-                if kernel_lock.repo_id == repo_id:
-                    return kernel_lock.sha
-    return None
-
-
-def _get_caller_distributions() -> List[Distribution]:
-    module = _get_caller_module()
-    if module is None:
-        return []
-
-    # Look up all possible distributions that this module could be from.
-    package = module.__name__.split(".")[0]
-    dist_names = importlib.metadata.packages_distributions().get(package)
-    if dist_names is None:
-        return []
-
-    return [importlib.metadata.distribution(dist_name) for dist_name in dist_names]
-
-
-def _get_caller_module() -> Optional[ModuleType]:
-    stack = inspect.stack()
-    # Get first module in the stack that is not the current module.
-    first_module = inspect.getmodule(stack[0][0])
-    for frame in stack[1:]:
-        module = inspect.getmodule(frame[0])
-        if module is not None and module != first_module:
-            return module
-    return first_module

src/kernels/__init__.py

@@ -0,0 +1,29 @@
+from kernels.layer import (
+    Device,
+    LayerRepository,
+    register_kernel_mapping,
+    replace_kernel_forward_from_hub,
+    use_kernel_forward_from_hub,
+    use_kernel_mapping,
+)
+from kernels.utils import (
+    get_kernel,
+    get_locked_kernel,
+    has_kernel,
+    install_kernel,
+    load_kernel,
+)
+
+__all__ = [
+    "get_kernel",
+    "get_locked_kernel",
+    "has_kernel",
+    "load_kernel",
+    "install_kernel",
+    "use_kernel_forward_from_hub",
+    "use_kernel_mapping",
+    "register_kernel_mapping",
+    "replace_kernel_forward_from_hub",
+    "LayerRepository",
+    "Device",
+]

src/kernels/cli.py

@@ -4,14 +4,14 @@ import json
 import sys
 from pathlib import Path
 
-from hf_kernels.compat import tomllib
-from hf_kernels.lockfile import KernelLock, get_kernel_locks
-from hf_kernels.utils import install_kernel, install_kernel_all_variants
+from kernels.compat import tomllib
+from kernels.lockfile import KernelLock, get_kernel_locks
+from kernels.utils import install_kernel, install_kernel_all_variants
 
 
 def main():
     parser = argparse.ArgumentParser(
-        prog="hf-kernel", description="Manage compute kernels"
+        prog="kernel", description="Manage compute kernels"
     )
     subparsers = parser.add_subparsers(required=True)
 
@@ -41,13 +41,13 @@ def main():
 
 
 def download_kernels(args):
-    lock_path = args.project_dir / "hf-kernels.lock"
+    lock_path = args.project_dir / "kernels.lock"
 
     if not lock_path.exists():
-        print(f"No hf-kernels.lock file found in: {args.project_dir}", file=sys.stderr)
+        print(f"No kernels.lock file found in: {args.project_dir}", file=sys.stderr)
         sys.exit(1)
 
-    with open(args.project_dir / "hf-kernels.lock", "r") as f:
+    with open(args.project_dir / "kernels.lock", "r") as f:
         lock_json = json.load(f)
 
     all_successful = True
@@ -59,10 +59,16 @@ def download_kernels(args):
             file=sys.stderr,
         )
         if args.all_variants:
-            install_kernel_all_variants(kernel_lock.repo_id, kernel_lock.sha)
+            install_kernel_all_variants(
+                kernel_lock.repo_id, kernel_lock.sha, variant_locks=kernel_lock.variants
+            )
         else:
             try:
-                install_kernel(kernel_lock.repo_id, kernel_lock.sha)
+                install_kernel(
+                    kernel_lock.repo_id,
+                    kernel_lock.sha,
+                    variant_locks=kernel_lock.variants,
+                )
             except FileNotFoundError as e:
                 print(e, file=sys.stderr)
                 all_successful = False
@@ -81,7 +87,7 @@ def lock_kernels(args):
     for kernel, version in kernel_versions.items():
         all_locks.append(get_kernel_locks(kernel, version))
 
-    with open(args.project_dir / "hf-kernels.lock", "w") as f:
+    with open(args.project_dir / "kernels.lock", "w") as f:
         json.dump(all_locks, f, cls=_JSONEncoder, indent=2)
 
 

src/kernels/layer.py

@@ -0,0 +1,264 @@
+import inspect
+import os
+import warnings
+from contextvars import ContextVar
+from copy import deepcopy
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING, Dict, Union
+
+from .utils import get_kernel
+
+if TYPE_CHECKING:
+    from torch import nn
+
+_DISABLE_KERNEL_MAPPING: bool = bool(int(os.environ.get("DISABLE_KERNEL_MAPPING", "0")))
+
+
+@dataclass(frozen=True)
+class Device:
+    type: str
+
+    # In the future we might add compute capabilities, etc.
+
+    def __eq__(self, other):
+        return isinstance(other, Device) and self.type == other.type
+
+    def __hash__(self):
+        return hash(self.type)
+
+
+@dataclass
+class LayerRepository:
+    """
+    Repository and name of a layer.
+    """
+
+    layer_name: str = field(
+        metadata={"help": "The name of the layer in the kernel repository."}
+    )
+    repo_id: str = field(metadata={"help": "The kernel hub repository with the layer."})
+    revision: str = field(
+        default="main", metadata={"help": "The revision of the layer."}
+    )
+
+    def __eq__(self, other):
+        return (
+            isinstance(other, LayerRepository)
+            and self.layer_name == other.layer_name
+            and self.repo_id == other.repo_id
+            and self.revision == other.revision
+        )
+
+    def __hash__(self):
+        return hash((self.layer_name, self.repo_id, self.revision))
+
+
+_KERNEL_MAPPING: ContextVar[Dict[str, Dict[Device, LayerRepository]]] = ContextVar(
+    "_KERNEL_MAPPING", default={}
+)
+
+
+def use_kernel_mapping(
+    mapping: Dict[str, Dict[Union[Device, str], LayerRepository]],
+    *,
+    inherit_mapping: bool = True,
+):
+    """
+    Context manager that sets a mapping for a duration of the context.
+
+    When `inherit_mapping` is set to `True` the current mapping will be
+    extended by `mapping` inside the context. If it is `False`, only
+    `mapping` is used inside the context.
+    """
+
+    class ContextManager:
+        def __enter__(self):
+            # Mappings always stack on previous mappings.
+            if inherit_mapping:
+                self.token = _KERNEL_MAPPING.set(deepcopy(_KERNEL_MAPPING.get()))
+            else:
+                self.token = _KERNEL_MAPPING.set({})
+            register_kernel_mapping(mapping)
+
+        def __exit__(self, exc_type, exc_value, traceback):
+            _KERNEL_MAPPING.reset(self.token)
+
+    return ContextManager()
+
+
+def register_kernel_mapping(
+    mapping: Dict[str, Dict[Union[Device, str], LayerRepository]]
+):
+    """
+    Allows one to register a mapping between a layer name the corresponding kernel to use, depending on the device.
+    This should be use in conjunction with `use_kernel_hub_forward` decorator on the classname.
+    Exemple usage:
+
+    ```python
+    from kernels import LayerRepository, register_kernel_mapping
+
+    kernel_layer_mapping = {
+      "LlamaRMSNorm": {
+          "cuda": LayerRepository(
+              repo_id="kernels-community/activation",
+              layer_name="RmsNorm",
+              revision="layers",
+          ),
+      },
+    }
+    register_kernel_mapping(kernel_layer_mapping)
+    ```
+    """
+    # Merge with existing mappings.
+    for new_kernel, new_device_repos in mapping.items():
+        device_repo = _KERNEL_MAPPING.get().setdefault(new_kernel, {})
+        for new_device, new_repo in new_device_repos.items():
+            if isinstance(new_device, str):
+                device_repo[Device(type=new_device)] = new_repo
+            else:
+                device_repo[new_device] = new_repo
+
+
+def replace_kernel_forward_from_hub(cls, layer_name: str, *, use_fallback: bool = True):
+    """
+    Replace the forward function of a layer using a layer from the kernel hub.
+    This function monkeypatches a layer, replacing the `forward` method
+    of the layer with that of a layer from the hub. The replacement is done
+    when a layer matching `layer_name` and device type is registered through
+    `register_layer_mapping`. The device type is inferred from the first
+    argument to `forward`.
+    """
+
+    fallback_forward = cls.forward
+
+    cached_layer: Dict[LayerRepository, nn.Module] = {}
+
+    def forward(self, x, *args, **kwargs):
+        if _DISABLE_KERNEL_MAPPING:
+            return fallback_forward(self, x, *args, **kwargs)
+
+        needs_backward = self.training
+        kernel = _KERNEL_MAPPING.get().get(layer_name)
+        if kernel is None:
+            warnings.warn(
+                "\n"
+                f"No kernel mapping found for layer `{layer_name}`. "
+                f"Check if the layer name matches one of the kernels in the mapping or add the kernel "
+                f"you want to use to the mapping. Defaulting to original forward implementation."
+            )
+            if not use_fallback:
+                raise ValueError(f"No layer mapping for `{layer_name}`")
+            return fallback_forward(self, x, *args, **kwargs)
+
+        device = getattr(x, "device", None)
+        if device is None:
+            return fallback_forward(self, x, *args, **kwargs)
+
+        repo = kernel.get(Device(type=device.type))
+        if repo is None:
+            if not use_fallback:
+                raise ValueError(
+                    f"No layer mapping for `{layer_name}` with device type `{device.type}`"
+                )
+            return fallback_forward(self, x, *args, **kwargs)
+
+        # Short-circuit if we already loaded the layer.
+        layer = cached_layer.get(repo, None)
+        if layer is not None:
+            if needs_backward and not getattr(layer, "has_backward", True):
+                return fallback_forward(self, x, *args, **kwargs)
+            return layer.forward(self, x, *args, **kwargs)
+
+        layer = _get_kernel_layer(
+            repo_id=repo.repo_id,
+            layer_name=repo.layer_name,
+            revision=repo.revision,
+        )
+
+        # We have to validate against the original signature.
+        orig_forward = cls.forward
+        try:
+            cls.forward = fallback_forward
+            _validate_layer(check_cls=cls, cls=layer)
+        finally:
+            cls.forward = orig_forward
+
+        cached_layer[repo] = layer
+
+        if needs_backward and not getattr(layer, "has_backward", True):
+            return fallback_forward(self, x, *args, **kwargs)
+        return layer.forward(self, x, *args, **kwargs)
+
+    cls.forward = forward
+
+
+def use_kernel_forward_from_hub(layer_name: str, *, use_fallback: bool = True):
+    """
+    Replace the forward function of a layer using a layer from the kernel hub.
+    This decorator can be applied to a layer and replaces the forward method
+    of the layer with that of a layer from the hub. The replacement is done
+    when a layer matching `layer_name` and device type is registered through
+    `register_layer_mapping`. The device type is inferred from the first
+    argument to `forward`.
+    """
+
+    def decorator(cls):
+        replace_kernel_forward_from_hub(cls, layer_name, use_fallback=use_fallback)
+        return cls
+
+    return decorator
+
+
+def _get_kernel_layer(*, repo_id: str, layer_name: str, revision: str) -> "nn.Module":
+    """Get a layer from a kernel."""
+
+    kernel = get_kernel(repo_id, revision=revision)
+
+    if getattr(kernel, "layers", None) is None:
+        raise ValueError(
+            f"Kernel `{repo_id}` at revision `{revision}` does not define any layers."
+        )
+
+    layer = getattr(kernel.layers, layer_name, None)
+    if layer is None:
+        raise ValueError(f"Layer `{layer_name}` not found in kernel `{repo_id}`.")
+    return layer
+
+
+def _validate_layer(*, check_cls, cls):
+    # The layer must have at least have the following properties: (1) it
+    # must be stateless; (2) the forward signature should correspond to
+    # the signature it is replacing; (3) forward should not call other
+    # methods.
+
+    from torch import nn
+
+    if not issubclass(cls, nn.Module):
+        raise TypeError(f"Layer `{cls}` is not a Torch layer.")
+
+    # We verify statelessness by checking that the does not have its own
+    # constructor (since the constructor could add member variables)...
+    if cls.__init__ is not nn.Module.__init__:
+        raise TypeError("Layer must not override nn.Module constructor.")
+
+    # ... or predefined member variables.
+    torch_module_members = {name for name, _ in inspect.getmembers(nn.Module)}
+    cls_members = {name for name, _ in inspect.getmembers(cls)}
+    difference = cls_members - torch_module_members
+    if difference != set() and difference != {"has_backward"}:
+        raise TypeError("Layer must not contain additional members.")
+
+    # Check whether the forward signatures are similar.
+    params = inspect.signature(cls.forward).parameters
+    ref_params = inspect.signature(check_cls.forward).parameters
+
+    if len(params) != len(ref_params):
+        raise TypeError(
+            "Forward signature does not match: different number of arguments."
+        )
+
+    for param, ref_param in zip(params.values(), ref_params.values()):
+        if param.kind != ref_param.kind:
+            raise TypeError(
+                f"Forward signature does not match: different kind of arguments ({param} ({param.kind}) and {ref_param} ({ref_param.kind})"
+            )

src/kernels/lockfile.py

@@ -1,33 +1,37 @@
+import hashlib
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Dict, List
+from typing import Dict, List, Tuple
 
 from huggingface_hub import HfApi
+from huggingface_hub.hf_api import GitRefInfo
 from packaging.specifiers import SpecifierSet
 from packaging.version import InvalidVersion, Version
 
-from hf_kernels.compat import tomllib
+from kernels.compat import tomllib
 
 
 @dataclass
-class FileLock:
-    filename: str
-    blob_id: str
+class VariantLock:
+    hash: str
+    hash_type: str = "git_lfs_concat"
 
 
 @dataclass
 class KernelLock:
     repo_id: str
     sha: str
-    files: List[FileLock]
+    variants: Dict[str, VariantLock]
 
     @classmethod
     def from_json(cls, o: Dict):
-        files = [FileLock(**f) for f in o["files"]]
-        return cls(repo_id=o["repo_id"], sha=o["sha"], files=files)
+        variants = {
+            variant: VariantLock(**lock) for variant, lock in o["variants"].items()
+        }
+        return cls(repo_id=o["repo_id"], sha=o["sha"], variants=variants)
 
 
-def _get_available_versions(repo_id: str):
+def _get_available_versions(repo_id: str) -> Dict[Version, GitRefInfo]:
     """Get kernel versions that are available in the repository."""
     versions = {}
     for tag in HfApi().list_repo_refs(repo_id).tags:
@@ -41,7 +45,7 @@ def _get_available_versions(repo_id: str):
     return versions
 
 
-def get_kernel_locks(repo_id: str, version_spec: str):
+def get_kernel_locks(repo_id: str, version_spec: str) -> KernelLock:
     """
     Get the locks for a kernel with the given version spec.
 
@@ -72,17 +76,36 @@ def get_kernel_locks(repo_id: str, version_spec: str):
             f"Cannot get sibling information for {repo_id} for tag {tag_for_newest.name}"
         )
 
-    file_locks = []
+    variant_files: Dict[str, List[Tuple[bytes, str]]] = {}
     for sibling in r.siblings:
         if sibling.rfilename.startswith("build/torch"):
             if sibling.blob_id is None:
                 raise ValueError(f"Cannot get blob ID for {sibling.rfilename}")
 
-            file_locks.append(
-                FileLock(filename=sibling.rfilename, blob_id=sibling.blob_id)
-            )
+            path = Path(sibling.rfilename)
+            variant = path.parts[1]
+            filename = Path(*path.parts[2:])
 
-    return KernelLock(repo_id=repo_id, sha=r.sha, files=file_locks)
+            hash = sibling.lfs.sha256 if sibling.lfs is not None else sibling.blob_id
+
+            files = variant_files.setdefault(variant, [])
+
+            # Encode as posix for consistent slash handling, then encode
+            # as utf-8 for byte-wise sorting later.
+            files.append((filename.as_posix().encode("utf-8"), hash))
+
+    variant_locks = {}
+    for variant, files in variant_files.items():
+        m = hashlib.sha256()
+        for filename_bytes, hash in sorted(files):
+            # Filename as bytes.
+            m.update(filename_bytes)
+            # Git blob or LFS file hash as bytes.
+            m.update(bytes.fromhex(hash))
+
+        variant_locks[variant] = VariantLock(hash=f"sha256-{m.hexdigest()}")
+
+    return KernelLock(repo_id=repo_id, sha=r.sha, variants=variant_locks)
 
 
 def write_egg_lockfile(cmd, basename, filename):
@@ -101,7 +124,7 @@ def write_egg_lockfile(cmd, basename, filename):
     if kernel_versions is None:
         return
 
-    lock_path = cwd / "hf-kernels.lock"
+    lock_path = cwd / "kernels.lock"
     if not lock_path.exists():
         logging.warning(f"Lock file {lock_path} does not exist")
         # Ensure that the file gets deleted in editable installs.

src/kernels/utils.py

@@ -0,0 +1,348 @@
+import ctypes
+import hashlib
+import importlib
+import importlib.metadata
+import inspect
+import json
+import logging
+import os
+import platform
+import sys
+from importlib.metadata import Distribution
+from pathlib import Path
+from types import ModuleType
+from typing import Dict, List, Optional, Tuple
+
+from huggingface_hub import file_exists, snapshot_download
+from packaging.version import parse
+
+from kernels.lockfile import KernelLock, VariantLock
+
+
+def _get_cache_dir() -> Optional[str]:
+    """Returns the kernels cache directory."""
+    cache_dir = os.environ.get("HF_KERNELS_CACHE", None)
+    if cache_dir is not None:
+        logging.warning(
+            "HF_KERNELS_CACHE will be removed in the future, use KERNELS_CACHE instead"
+        )
+        return cache_dir
+
+    return os.environ.get("KERNELS_CACHE", None)
+
+
+CACHE_DIR: Optional[str] = _get_cache_dir()
+
+
+def build_variant() -> str:
+    import torch
+
+    if torch.version.cuda is not None:
+        cuda_version = parse(torch.version.cuda)
+        compute_framework = f"cu{cuda_version.major}{cuda_version.minor}"
+    elif torch.version.hip is not None:
+        rocm_version = parse(torch.version.hip.split("-")[0])
+        compute_framework = f"rocm{rocm_version.major}{rocm_version.minor}"
+    else:
+        raise AssertionError("Torch was not compiled with CUDA or ROCm enabled.")
+
+    torch_version = parse(torch.__version__)
+    cxxabi = "cxx11" if torch.compiled_with_cxx11_abi() else "cxx98"
+    cpu = platform.machine()
+    os = platform.system().lower()
+
+    return f"torch{torch_version.major}{torch_version.minor}-{cxxabi}-{compute_framework}-{cpu}-{os}"
+
+
+def universal_build_variant() -> str:
+    # Once we support other frameworks, detection goes here.
+    return "torch-universal"
+
+
+def import_from_path(module_name: str, file_path: Path) -> ModuleType:
+    # We cannot use the module name as-is, after adding it to `sys.modules`,
+    # it would also be used for other imports. So, we make a module name that
+    # depends on the path for it to be unique using the hex-encoded hash of
+    # the path.
+    path_hash = "{:x}".format(ctypes.c_size_t(hash(file_path)).value)
+    module_name = f"{module_name}_{path_hash}"
+    spec = importlib.util.spec_from_file_location(module_name, file_path)
+    if spec is None:
+        raise ImportError(f"Cannot load spec for {module_name} from {file_path}")
+    module = importlib.util.module_from_spec(spec)
+    if module is None:
+        raise ImportError(f"Cannot load module {module_name} from spec")
+    sys.modules[module_name] = module
+    spec.loader.exec_module(module)  # type: ignore
+    return module
+
+
+def install_kernel(
+    repo_id: str,
+    revision: str,
+    local_files_only: bool = False,
+    variant_locks: Optional[Dict[str, VariantLock]] = None,
+) -> Tuple[str, Path]:
+    """
+    Download a kernel for the current environment to the cache.
+
+    The output path is validated againt `hash` when set.
+    """
+    package_name = package_name_from_repo_id(repo_id)
+    variant = build_variant()
+    universal_variant = universal_build_variant()
+    repo_path = Path(
+        snapshot_download(
+            repo_id,
+            allow_patterns=[f"build/{variant}/*", f"build/{universal_variant}/*"],
+            cache_dir=CACHE_DIR,
+            revision=revision,
+            local_files_only=local_files_only,
+        )
+    )
+
+    variant_path = repo_path / "build" / variant
+    universal_variant_path = repo_path / "build" / universal_variant
+
+    if not variant_path.exists() and universal_variant_path.exists():
+        # Fall back to universal variant.
+        variant = universal_variant
+        variant_path = universal_variant_path
+
+    if variant_locks is not None:
+        variant_lock = variant_locks.get(variant)
+        if variant_lock is None:
+            raise ValueError(f"No lock found for build variant: {variant}")
+        validate_kernel(repo_path=repo_path, variant=variant, hash=variant_lock.hash)
+
+    module_init_path = variant_path / package_name / "__init__.py"
+
+    if not os.path.exists(module_init_path):
+        raise FileNotFoundError(
+            f"Kernel `{repo_id}` at revision {revision} does not have build: {variant}"
+        )
+
+    return package_name, variant_path
+
+
+def install_kernel_all_variants(
+    repo_id: str,
+    revision: str,
+    local_files_only: bool = False,
+    variant_locks: Optional[Dict[str, VariantLock]] = None,
+) -> Path:
+    repo_path = Path(
+        snapshot_download(
+            repo_id,
+            allow_patterns="build/*",
+            cache_dir=CACHE_DIR,
+            revision=revision,
+            local_files_only=local_files_only,
+        )
+    )
+
+    if variant_locks is not None:
+        for entry in (repo_path / "build").iterdir():
+            variant = entry.parts[-1]
+
+            variant_lock = variant_locks.get(variant)
+            if variant_lock is None:
+                raise ValueError(f"No lock found for build variant: {variant}")
+
+            validate_kernel(
+                repo_path=repo_path, variant=variant, hash=variant_lock.hash
+            )
+
+    return repo_path / "build"
+
+
+def get_kernel(repo_id: str, revision: str = "main") -> ModuleType:
+    package_name, package_path = install_kernel(repo_id, revision=revision)
+    return import_from_path(package_name, package_path / package_name / "__init__.py")
+
+
+def has_kernel(repo_id: str, revision: str = "main") -> bool:
+    """
+    Check whether a kernel build exists for the current environment
+    (Torch version and compute framework).
+    """
+    package_name = package_name_from_repo_id(repo_id)
+    variant = build_variant()
+    universal_variant = universal_build_variant()
+
+    if file_exists(
+        repo_id,
+        revision=revision,
+        filename=f"build/{universal_variant}/{package_name}/__init__.py",
+    ):
+        return True
+
+    return file_exists(
+        repo_id,
+        revision=revision,
+        filename=f"build/{variant}/{package_name}/__init__.py",
+    )
+
+
+def load_kernel(repo_id: str, *, lockfile: Optional[Path] = None) -> ModuleType:
+    """
+    Get a pre-downloaded, locked kernel.
+
+    If `lockfile` is not specified, the lockfile will be loaded from the
+    caller's package metadata.
+    """
+    if lockfile is None:
+        locked_sha = _get_caller_locked_kernel(repo_id)
+    else:
+        with open(lockfile, "r") as f:
+            locked_sha = _get_locked_kernel(repo_id, f.read())
+
+    if locked_sha is None:
+        raise ValueError(
+            f"Kernel `{repo_id}` is not locked. Please lock it with `kernels lock <project>` and then reinstall the project."
+        )
+
+    package_name = package_name_from_repo_id(repo_id)
+
+    variant = build_variant()
+    universal_variant = universal_build_variant()
+
+    repo_path = Path(
+        snapshot_download(
+            repo_id,
+            allow_patterns=[f"build/{variant}/*", f"build/{universal_variant}/*"],
+            cache_dir=CACHE_DIR,
+            revision=locked_sha,
+            local_files_only=True,
+        )
+    )
+
+    variant_path = repo_path / "build" / variant
+    universal_variant_path = repo_path / "build" / universal_variant
+    if not variant_path.exists() and universal_variant_path.exists():
+        # Fall back to universal variant.
+        variant = universal_variant
+        variant_path = universal_variant_path
+
+    module_init_path = variant_path / package_name / "__init__.py"
+    if not os.path.exists(module_init_path):
+        raise FileNotFoundError(
+            f"Locked kernel `{repo_id}` does not have build `{variant}` or was not downloaded with `kernels download <project>`"
+        )
+
+    return import_from_path(package_name, variant_path / package_name / "__init__.py")
+
+
+def get_locked_kernel(repo_id: str, local_files_only: bool = False) -> ModuleType:
+    """Get a kernel using a lock file."""
+    locked_sha = _get_caller_locked_kernel(repo_id)
+
+    if locked_sha is None:
+        raise ValueError(f"Kernel `{repo_id}` is not locked")
+
+    package_name, package_path = install_kernel(
+        repo_id, locked_sha, local_files_only=local_files_only
+    )
+
+    return import_from_path(package_name, package_path / package_name / "__init__.py")
+
+
+def _get_caller_locked_kernel(repo_id: str) -> Optional[str]:
+    for dist in _get_caller_distributions():
+        lock_json = dist.read_text("kernels.lock")
+        if lock_json is None:
+            continue
+        locked_sha = _get_locked_kernel(repo_id, lock_json)
+        if locked_sha is not None:
+            return locked_sha
+    return None
+
+
+def _get_locked_kernel(repo_id: str, lock_json: str) -> Optional[str]:
+    for kernel_lock_json in json.loads(lock_json):
+        kernel_lock = KernelLock.from_json(kernel_lock_json)
+        if kernel_lock.repo_id == repo_id:
+            return kernel_lock.sha
+    return None
+
+
+def _get_caller_distributions() -> List[Distribution]:
+    module = _get_caller_module()
+    if module is None:
+        return []
+
+    # Look up all possible distributions that this module could be from.
+    package = module.__name__.split(".")[0]
+    dist_names = importlib.metadata.packages_distributions().get(package)
+    if dist_names is None:
+        return []
+
+    return [importlib.metadata.distribution(dist_name) for dist_name in dist_names]
+
+
+def _get_caller_module() -> Optional[ModuleType]:
+    stack = inspect.stack()
+    # Get first module in the stack that is not the current module.
+    first_module = inspect.getmodule(stack[0][0])
+    for frame in stack[1:]:
+        module = inspect.getmodule(frame[0])
+        if module is not None and module != first_module:
+            return module
+    return first_module
+
+
+def validate_kernel(*, repo_path: Path, variant: str, hash: str):
+    """Validate the given build variant of a kernel against a hasht."""
+    variant_path = repo_path / "build" / variant
+
+    # Get the file paths. The first element is a byte-encoded relative path
+    # used for sorting. The second element is the absolute path.
+    files: List[Tuple[bytes, Path]] = []
+    # Ideally we'd use Path.walk, but it's only available in Python 3.12.
+    for dirpath, _, filenames in os.walk(variant_path):
+        for filename in filenames:
+            file_abs = Path(dirpath) / filename
+
+            # Python likes to create files when importing modules from the
+            # cache, only hash files that are symlinked blobs.
+            if file_abs.is_symlink():
+                files.append(
+                    (
+                        file_abs.relative_to(variant_path).as_posix().encode("utf-8"),
+                        file_abs,
+                    )
+                )
+
+    m = hashlib.sha256()
+
+    for filename_bytes, full_path in sorted(files):
+        m.update(filename_bytes)
+
+        blob_filename = full_path.resolve().name
+        if len(blob_filename) == 40:
+            # SHA-1 hashed, so a Git blob.
+            m.update(git_hash_object(full_path.read_bytes()))
+        elif len(blob_filename) == 64:
+            # SHA-256 hashed, so a Git LFS blob.
+            m.update(hashlib.sha256(full_path.read_bytes()).digest())
+        else:
+            raise ValueError(f"Unexpected blob filename length: {len(blob_filename)}")
+
+    computedHash = f"sha256-{m.hexdigest()}"
+    if computedHash != hash:
+        raise ValueError(
+            f"Lock file specifies kernel with hash {hash}, but downloaded kernel has hash: {computedHash}"
+        )
+
+
+def git_hash_object(data: bytes, object_type: str = "blob"):
+    """Calculate git SHA1 of data."""
+    header = f"{object_type} {len(data)}\0".encode()
+    m = hashlib.sha1()
+    m.update(header)
+    m.update(data)
+    return m.digest()
+
+
+def package_name_from_repo_id(repo_id: str) -> str:
+    return repo_id.split("/")[-1].replace("-", "_")

tests/kernel_locking/kernels.lock

@@ -0,0 +1,66 @@
+[
+  {
+    "repo_id": "kernels-community/activation",
+    "sha": "6a030420d0dd33ffdc1281afc8ae8e94b4f4f9d0",
+    "variants": {
+      "torch25-cxx11-cu118-x86_64-linux": {
+        "hash": "sha256-3e39de10721a6b21806834fc95c96526b9cfe2c2052829184f2d3fa48ef5849d",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch25-cxx11-cu121-x86_64-linux": {
+        "hash": "sha256-b0dee22c65bb277fa8150f9ea3fc90e2b1c11f84b5d760bbf4ab9c7a4b102e58",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch25-cxx11-cu124-x86_64-linux": {
+        "hash": "sha256-8960cf857d641d591a7c2d4264925cc2bf7b4a6f9d738b74082b2fb0806db19a",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch25-cxx98-cu118-x86_64-linux": {
+        "hash": "sha256-0496e04c2900a2dc7ab0f3b95fe8ce9da69faab6b5ca3f55ddd62c26c81268d0",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch25-cxx98-cu121-x86_64-linux": {
+        "hash": "sha256-172b793b24dfed3dcb9adc7d3487f260c05b310c598fc6ee8abb3e230c59a0a8",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch25-cxx98-cu124-x86_64-linux": {
+        "hash": "sha256-12f5e66f32dc4cf4b21f43f76efad198556024da67a1ce28e88ea2d49ad8bdcc",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch26-cxx11-cu118-x86_64-linux": {
+        "hash": "sha256-bb70e2f36f0b4d12868956c2ad713c756570ff0e0eb4cf7fc3a78ebde617975b",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch26-cxx11-cu124-x86_64-linux": {
+        "hash": "sha256-a745732eb9ec5d6a54565dbeec5b3c983cc6aa072a4a2576ab2fef9b2a600005",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch26-cxx11-cu126-x86_64-linux": {
+        "hash": "sha256-1160684ca09c065864f27c5c110281807a1ec31d603bf05fcb974e9e7cfe35cc",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch26-cxx98-cu118-x86_64-linux": {
+        "hash": "sha256-24459d068943b93e4d55e94811469bf7e850d7958785132b108f1240724b846f",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch26-cxx98-cu124-x86_64-linux": {
+        "hash": "sha256-5b009ba63ab6d52ac1aaf70057a2d0fa6ea5d1788a2416111be02103c6bcaaaf",
+        "hash_type": "git_lfs_concat"
+      },
+      "torch26-cxx98-cu126-x86_64-linux": {
+        "hash": "sha256-05128889b4bdaf9ef58f3c07d93218deaa08e06f9121931b47efef8826482e4a",
+        "hash_type": "git_lfs_concat"
+      }
+    }
+  },
+  {
+    "repo_id": "kernels-community/triton-scaled-mm",
+    "sha": "af10d8c1affe8efce93d228c3e6e64ff673d493f",
+    "variants": {
+      "torch-universal": {
+        "hash": "sha256-b843c5f30b52b6c1c56fca28cb0cf453be71d6ce7d308f383dce71a8050f7b52",
+        "hash_type": "git_lfs_concat"
+      }
+    }
+  }
+]

tests/kernel_locking/pyproject.toml

@@ -0,0 +1,3 @@
+[tool.kernels.dependencies]
+"kernels-community/activation" = ">=0.0.2"
+"kernels-community/triton-scaled-mm" = ">=0.0.2"

tests/test_basic.py

@@ -1,6 +1,7 @@
 import pytest
 import torch
-from hf_kernels import get_kernel
+
+from kernels import get_kernel, has_kernel
 
 
 @pytest.fixture
@@ -8,6 +9,11 @@ def kernel():
     return get_kernel("kernels-community/activation")
 
 
+@pytest.fixture
+def universal_kernel():
+    return get_kernel("kernels-community/triton-scaled-mm")
+
+
 @pytest.fixture
 def device():
     if not torch.cuda.is_available():
@@ -28,3 +34,33 @@ def test_gelu_fast(kernel, device):
     )
 
     assert torch.allclose(y, expected)
+
+
+@pytest.mark.parametrize(
+    "kernel_exists",
+    [
+        ("kernels-community/activation", "main", True),
+        ("kernels-community/triton-layer-norm", "main", True),
+        # Repo only contains Torch 2.4 kernels (and we don't
+        # support/test against this version).
+        ("kernels-test/only-torch-2.4", "main", False),
+        ("google-bert/bert-base-uncased", "87565a309", False),
+    ],
+)
+def test_has_kernel(kernel_exists):
+    repo_id, revision, kernel = kernel_exists
+    assert has_kernel(repo_id, revision=revision) == kernel
+
+
+def test_universal_kernel(universal_kernel):
+    torch.manual_seed(0)
+    A = torch.randint(-10, 10, (64, 128), dtype=torch.int8, device="cuda")
+    B = torch.randint(-10, 10, (128, 96), dtype=torch.int8, device="cuda")
+    scale_a = torch.tensor(0.4, dtype=torch.float16, device="cuda")
+    scale_b = torch.tensor(0.6, dtype=torch.float16, device="cuda")
+
+    out = universal_kernel.triton_scaled_mm(A, B, scale_a, scale_b, torch.float16)
+    out_check = (A * scale_a) @ (B * scale_b)
+    out_check = out_check.to(torch.float16)
+
+    torch.testing.assert_close(out, out_check, rtol=1e-1, atol=1e-1)

tests/test_benchmarks.py

@@ -1,6 +1,7 @@
 import pytest
 import torch
-from hf_kernels import get_kernel
+
+from kernels import get_kernel
 
 
 @pytest.fixture

tests/test_kernel_locking.py

@@ -0,0 +1,24 @@
+from dataclasses import dataclass
+from pathlib import Path
+
+from kernels import load_kernel
+from kernels.cli import download_kernels
+
+
+# Mock download arguments class.
+@dataclass
+class DownloadArgs:
+    all_variants: bool
+    project_dir: Path
+
+
+def test_download_all_hash_validation():
+    project_dir = Path(__file__).parent / "kernel_locking"
+    download_kernels(DownloadArgs(all_variants=True, project_dir=project_dir))
+
+
+def test_load_locked():
+    project_dir = Path(__file__).parent / "kernel_locking"
+    # Also validates that hashing works correctly.
+    download_kernels(DownloadArgs(all_variants=False, project_dir=project_dir))
+    load_kernel("kernels-community/activation", lockfile=project_dir / "kernels.lock")

tests/test_layer.py

@@ -0,0 +1,277 @@
+import pytest
+import torch
+import torch.nn as nn
+from torch.nn import functional as F
+
+from kernels import (
+    Device,
+    LayerRepository,
+    register_kernel_mapping,
+    use_kernel_forward_from_hub,
+)
+from kernels.layer import _KERNEL_MAPPING, _validate_layer, use_kernel_mapping
+
+kernel_layer_mapping = {
+    "SiluAndMul": {
+        Device(type="cuda"): LayerRepository(
+            repo_id="kernels-community/activation",
+            layer_name="SiluAndMul",
+            revision="layers",
+        )
+    },
+    "SiluAndMulStringDevice": {
+        "cuda": LayerRepository(
+            repo_id="kernels-community/activation",
+            layer_name="SiluAndMul",
+            revision="layers",
+        )
+    },
+}
+
+register_kernel_mapping(kernel_layer_mapping)
+
+
+class SiluAndMul(nn.Module):
+    def __init__(self):
+        super().__init__()
+        # Used to check that we called hub kernel.
+        self.n_calls = 0
+
+    def forward(self, input: torch.Tensor) -> torch.Tensor:
+        self.n_calls += 1
+        d = input.shape[-1] // 2
+        return F.silu(input[..., :d]) * input[..., d:]
+
+
+@use_kernel_forward_from_hub("SiluAndMul")
+class SiluAndMulWithKernel(SiluAndMul):
+    pass
+
+
+@use_kernel_forward_from_hub("SiluAndMulStringDevice")
+class SiluAndMulStringDevice(SiluAndMul):
+    pass
+
+
+def test_arg_kinds():
+    @use_kernel_forward_from_hub("ArgKind")
+    class ArgKind(nn.Module):
+        def forward(
+            self,
+            arg1,
+            arg2,
+            *,
+            kwarg1,
+            kwarg2=42,
+        ):
+            return (arg1, arg2, kwarg1, kwarg2)
+
+    arg_kind = ArgKind()
+    assert arg_kind("foo", "bar", kwarg1="baz") == ("foo", "bar", "baz", 42)
+    assert arg_kind("foo", "bar", kwarg1="baz", kwarg2=5) == ("foo", "bar", "baz", 5)
+
+
+@pytest.mark.parametrize("cls", [SiluAndMulWithKernel, SiluAndMulStringDevice])
+@pytest.mark.parametrize("device", ["cuda", "cpu"])
+def test_hub_forward(cls, device):
+    torch.random.manual_seed(0)
+
+    silu_and_mul = SiluAndMul()
+    X = torch.randn((32, 64), device=device)
+    Y = silu_and_mul(X)
+
+    silu_and_mul_with_kernel = cls()
+    Y_kernel = silu_and_mul_with_kernel(X)
+
+    torch.testing.assert_close(Y_kernel, Y)
+
+    assert silu_and_mul.n_calls == 1
+    if device == "cuda":
+        assert silu_and_mul_with_kernel.n_calls == 0
+    else:
+        assert silu_and_mul_with_kernel.n_calls == 1
+
+
+def test_layer_fallback_works():
+    @use_kernel_forward_from_hub("SiluAndMulNonExisting")
+    class SiluAndMulWithKernelFallback(SiluAndMul):
+        pass
+
+    # Check that we don't raise an exception for a non-existing kernel.
+    SiluAndMulWithKernelFallback()
+
+
+def test_mapping_contexts():
+    assert set(_KERNEL_MAPPING.get().keys()) == {"SiluAndMul", "SiluAndMulStringDevice"}
+
+    extra_mapping1 = {
+        "TestKernel": {
+            Device(type="cuda"): LayerRepository(
+                repo_id="kernels-community/activation",
+                layer_name="SiluAndMul",
+                revision="layers",
+            )
+        }
+    }
+
+    with use_kernel_mapping(extra_mapping1):
+        assert set(_KERNEL_MAPPING.get().keys()) == {
+            "SiluAndMul",
+            "SiluAndMulStringDevice",
+            "TestKernel",
+        }
+
+        extra_mapping2 = {
+            "SiluAndMul": {
+                Device(type="cuda"): LayerRepository(
+                    repo_id="kernels-community/non-existing",
+                    layer_name="SiluAndMul",
+                    revision="layers",
+                )
+            }
+        }
+
+        with use_kernel_mapping(extra_mapping2):
+            assert set(_KERNEL_MAPPING.get().keys()) == {
+                "SiluAndMul",
+                "SiluAndMulStringDevice",
+                "TestKernel",
+            }
+            assert (
+                _KERNEL_MAPPING.get()["SiluAndMul"][Device(type="cuda")].repo_id
+                == "kernels-community/non-existing"
+            )
+
+        assert set(_KERNEL_MAPPING.get().keys()) == {
+            "SiluAndMul",
+            "SiluAndMulStringDevice",
+            "TestKernel",
+        }
+        assert (
+            _KERNEL_MAPPING.get()["SiluAndMul"][Device(type="cuda")].repo_id
+            == "kernels-community/activation"
+        )
+
+        with use_kernel_mapping(extra_mapping2, inherit_mapping=False):
+            assert set(_KERNEL_MAPPING.get().keys()) == {
+                "SiluAndMul",
+            }
+            assert (
+                _KERNEL_MAPPING.get()["SiluAndMul"][Device(type="cuda")].repo_id
+                == "kernels-community/non-existing"
+            )
+
+        assert set(_KERNEL_MAPPING.get().keys()) == {
+            "SiluAndMul",
+            "SiluAndMulStringDevice",
+            "TestKernel",
+        }
+        assert (
+            _KERNEL_MAPPING.get()["SiluAndMul"][Device(type="cuda")].repo_id
+            == "kernels-community/activation"
+        )
+
+    assert set(_KERNEL_MAPPING.get().keys()) == {
+        "SiluAndMul",
+        "SiluAndMulStringDevice",
+    }
+
+
+def test_validate_kernel_layer():
+    class BadLayer(nn.Module):
+        def __init__(self, *args, **kwargs):
+            super().__init__(*args, **kwargs)
+            self.foo = 42
+
+    with pytest.raises(TypeError, match="not override"):
+        _validate_layer(cls=BadLayer, check_cls=SiluAndMul)
+
+    class BadLayer2(nn.Module):
+        foo: int = 42
+
+    with pytest.raises(TypeError, match="not contain additional members"):
+        _validate_layer(cls=BadLayer2, check_cls=SiluAndMul)
+
+    class BadLayer3(nn.Module):
+        def forward(self, x: torch.Tensor, foo: int) -> torch.Tensor: ...
+
+    with pytest.raises(TypeError, match="different number of arguments"):
+        _validate_layer(cls=BadLayer3, check_cls=SiluAndMul)
+
+    class BadLayer4(nn.Module):
+        def forward(self, *, x: torch.Tensor) -> torch.Tensor: ...
+
+    with pytest.raises(TypeError, match="different kind of arguments"):
+        _validate_layer(cls=BadLayer4, check_cls=SiluAndMul)
+
+
+def test_fallback_used_when_training():
+    @use_kernel_forward_from_hub("Linear")
+    class TorchLinear(nn.Linear):
+        def __init__(self, *args, **kwargs):
+            super().__init__(*args, **kwargs)
+            # Used to check that we called hub kernel.
+            self.n_calls = 0
+
+        def forward(self, input: torch.Tensor) -> torch.Tensor:
+            self.n_calls += 1
+            return super().forward(input)
+
+    linear = TorchLinear(32, 32).to("cuda")
+
+    with use_kernel_mapping(
+        {
+            "Linear": {
+                Device(type="cuda"): LayerRepository(
+                    repo_id="kernels-test/backward-marker-test",
+                    layer_name="LinearImplicitBackward",
+                )
+            }
+        }
+    ):
+        linear.train()
+        X = torch.randn(10, 32, device="cuda")
+        linear(X)
+        assert linear.n_calls == 0
+
+        linear.eval()
+        linear(X)
+        assert linear.n_calls == 0
+
+    with use_kernel_mapping(
+        {
+            "Linear": {
+                Device(type="cuda"): LayerRepository(
+                    repo_id="kernels-test/backward-marker-test",
+                    layer_name="LinearBackward",
+                )
+            }
+        }
+    ):
+        linear.train()
+        X = torch.randn(10, 32, device="cuda")
+        linear(X)
+        assert linear.n_calls == 0
+
+        linear.eval()
+        linear(X)
+        assert linear.n_calls == 0
+
+    with use_kernel_mapping(
+        {
+            "Linear": {
+                Device(type="cuda"): LayerRepository(
+                    repo_id="kernels-test/backward-marker-test",
+                    layer_name="LinearNoBackward",
+                )
+            }
+        }
+    ):
+        linear.train()
+        X = torch.randn(10, 32, device="cuda")
+        linear(X)
+        assert linear.n_calls == 1
+
+        linear.eval()
+        linear(X)
+        assert linear.n_calls == 1