Add publishing workflow (#81)

* Allow layers to opt in to `torch.compile`

This change allows a layer to set the `can_torch_compile` class
variable to indicate that the layer is compatible with `torch.compile`.
When enabled, the layer does not fall back to the original
implementation when `torch.compile` is used.

* Comment fixes

Co-authored-by: Mohamed Mekkouri <93391238+MekkCyber@users.noreply.github.com>

---------

Co-authored-by: Mohamed Mekkouri <93391238+MekkCyber@users.noreply.github.com>

.github/workflows/publish.yml

@@ -0,0 +1,120 @@
+name: Publish Python 🐍 distribution 📦 to PyPI and TestPyPI
+
+on: push
+
+jobs:
+  build:
+    name: Build distribution 📦
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.9"
+      - name: Install pypa/build
+        run: >-
+          python3 -m
+          pip install
+          build
+          --user
+      - name: Build a binary wheel and a source tarball
+        run: python3 -m build
+      - name: Store the distribution packages
+        uses: actions/upload-artifact@v4
+        with:
+          name: python-package-distributions
+          path: dist/
+
+  publish-to-pypi:
+    name: >-
+      Publish Python 🐍 distribution 📦 to PyPI
+    if: startsWith(github.ref, 'refs/tags/') # only publish to PyPI on tag pushes
+    needs:
+      - build
+    runs-on: ubuntu-latest
+    environment:
+      name: pypi
+      url: https://pypi.org/p/<package-name> # Replace <package-name> with your PyPI project name
+    permissions:
+      id-token: write # IMPORTANT: mandatory for trusted publishing
+
+    steps:
+      - name: Download all the dists
+        uses: actions/download-artifact@v4
+        with:
+          name: python-package-distributions
+          path: dist/
+      - name: Publish distribution 📦 to PyPI
+        uses: pypa/gh-action-pypi-publish@release/v1
+
+  github-release:
+    name: >-
+      Sign the Python 🐍 distribution 📦 with Sigstore
+      and upload them to GitHub Release
+    needs:
+      - publish-to-pypi
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: write # IMPORTANT: mandatory for making GitHub Releases
+      id-token: write # IMPORTANT: mandatory for sigstore
+
+    steps:
+      - name: Download all the dists
+        uses: actions/download-artifact@v4
+        with:
+          name: python-package-distributions
+          path: dist/
+      - name: Sign the dists with Sigstore
+        uses: sigstore/gh-action-sigstore-python@v3.0.0
+        with:
+          inputs: >-
+            ./dist/*.tar.gz
+            ./dist/*.whl
+      - name: Create GitHub Release
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        run: >-
+          gh release create
+          "$GITHUB_REF_NAME"
+          --repo "$GITHUB_REPOSITORY"
+          --notes ""
+      - name: Upload artifact signatures to GitHub Release
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        # Upload to GitHub Release using the `gh` CLI.
+        # `dist/` contains the built packages, and the
+        # sigstore-produced signatures and certificates.
+        run: >-
+          gh release upload
+          "$GITHUB_REF_NAME" dist/**
+          --repo "$GITHUB_REPOSITORY"
+
+  publish-to-testpypi:
+    name: Publish Python 🐍 distribution 📦 to TestPyPI
+    needs:
+      - build
+    runs-on: ubuntu-latest
+
+    environment:
+      name: testpypi
+      url: https://test.pypi.org/p/<package-name>
+
+    permissions:
+      id-token: write # IMPORTANT: mandatory for trusted publishing
+
+    steps:
+      - name: Download all the dists
+        uses: actions/download-artifact@v4
+        with:
+          name: python-package-distributions
+          path: dist/
+      - name: Publish distribution 📦 to TestPyPI
+        uses: pypa/gh-action-pypi-publish@release/v1
+        with:
+          repository-url: https://test.pypi.org/legacy/
+          skip-existing: true # Only upload when the version is unique.

.github/workflows/test.yml

@@ -52,3 +52,8 @@ jobs:
 
       - name: Run tests
         run: uv run pytest tests
+
+      - name: Import check without torch
+        run: |
+          uv pip uninstall torch
+          python -c "import kernels"

LICENSE

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README.md

@@ -1,5 +1,16 @@
 # kernels
 
+<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
@@ -45,7 +56,9 @@ the Hub.
 
 ## 📚 Documentation
 
+- [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/)

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

@@ -1,8 +1,11 @@
 # Kernel requirements
 
-Kernels on the Hub must fulfill the requirements outlined on this page.
+Kernels on the Hub must fulfill the requirements outlined on this page. By
+ensuring kernels are compliant, they can be used on a wide range of Linux
+systems and Torch builds.
+
 You can use [kernel-builder](https://github.com/huggingface/kernel-builder/)
-to build conforming kernels.
+to build compliant kernels.
 
 ## Directory layout
 
@@ -10,34 +13,27 @@ 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:
+For example `build/torch26-cxx98-cu118-x86_64-linux`.
 
-- `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
+Each variant directory must 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.
 
+## Build variants
+
+A kernel can be compliant for a specific compute framework (e.g. CUDA) or
+architecture (e.g. x86_64). For compliance with a compute framework and
+architecture combination, all the variants from the [build variant list](https://github.com/huggingface/kernel-builder/blob/main/docs/build-variants.md)
+must be available for that combination.
+
+## 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
@@ -46,16 +42,31 @@ 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 glibc 2.27 or later. This means that no symbols
-  from later versions must be used. To archive this, the module should
-  be built against this glibc version. **Warning:** libgcc must also be
-  built against glibc 2.27 to avoid leaking symbols.
-- No dynamic linkage against libstdc++/libc++. Linkage for C++ symbols
-  must be static.
-- No dynamic library dependencies outside Torch or CUDA libraries
-  installed as dependencies of Torch.
+- 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:
 
-(These requirements will be updated as new PyTorch versions are released.)
+  - 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
 
@@ -76,6 +87,90 @@ 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.
+
+There are two exceptions to the _no class variables rule_:
+
+1. The `has_backward` variable can be used to indicate whether the layer has
+   a backward pass implemented (`True` when absent).
+2. The `can_torch_compile` variable can be used to indicate whether the layer
+   supports `torch.compile` (`False` 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.

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

@@ -13,7 +13,7 @@ build-backend = "setuptools.build_meta"
 "kernels-community/activation" = ">=0.0.1"
 ```
 
-Then run `kernel lock .` in the project directory. This generates a `kernels.lock` file with
+Then run `kernels 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`:
 
@@ -28,7 +28,7 @@ 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
+Locked kernels can be pre-downloaded by running `kernels download .` in your
 project directory. This will download the kernels to your local Hugging Face
 Hub cache.
 

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

@@ -1,6 +1,6 @@
 [project]
 name = "kernels"
-version = "0.2.1"
+version = "0.5.0.dev0"
 description = "Download compute kernels"
 authors = [
   { name = "OlivierDehaene", email = "olivier@huggingface.co" },
@@ -8,13 +8,13 @@ authors = [
   { 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>=2.5",
+  "huggingface_hub>=0.26.0,<1.0",
+  "packaging>=20.0",
+  "tomli>=2.0; python_version<'3.11'",
 ]
 
 [build-system]
@@ -27,8 +27,12 @@ dev = [
   "pytest >=8",
   # Whatever version is compatible with pytest.
   "pytest-benchmark",
+  "torch >=2.5",
 ]
 
+[project.optional-dependencies]
+torch = ["torch"]
+
 [project.scripts]
 kernels = "kernels.cli:main"
 

src/kernels/__init__.py

@@ -1,3 +1,29 @@
-from kernels.utils import get_kernel, get_locked_kernel, install_kernel, load_kernel
+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", "load_kernel", "install_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/layer.py

@@ -0,0 +1,297 @@
+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
+        is_compiling = _is_torchdynamo_compiling()
+
+        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:
+            # Switch to fallback when the layer does not support:
+            # compilation/compile when needed.
+            # backward when needed
+            needs_fallback = needs_backward and not getattr(layer, "has_backward", True)
+            needs_fallback |= is_compiling and not getattr(
+                layer, "can_torch_compile", False
+            )
+            if needs_fallback:
+                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
+
+        # Switch to fallback when the layer does not support
+        # compilation/compile when needed.
+        needs_fallback = needs_backward and not getattr(layer, "has_backward", True)
+        needs_fallback |= is_compiling and not getattr(
+            layer, "can_torch_compile", False
+        )
+        if needs_fallback:
+            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
+    # verify if : difference ⊄ {"can_torch_compile", "has_backward"}
+    if not difference <= {"can_torch_compile", "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})"
+            )
+
+
+def _is_torchdynamo_compiling():
+    # Importing torch._dynamo causes issues with PyTorch profiler (https://github.com/pytorch/pytorch/issues/130622)
+    # hence rather relying on `torch.compiler.is_compiling()` when possible (torch>=2.3)
+    try:
+        import torch
+
+        return torch.compiler.is_compiling()
+    except Exception:
+        try:
+            import torch._dynamo as dynamo  # noqa: F401
+
+            return dynamo.is_compiling()
+        except Exception:
+            return False

src/kernels/utils.py

@@ -4,6 +4,7 @@ import importlib
 import importlib.metadata
 import inspect
 import json
+import logging
 import os
 import platform
 import sys
@@ -12,29 +13,45 @@ from pathlib import Path
 from types import ModuleType
 from typing import Dict, List, Optional, Tuple
 
-from huggingface_hub import snapshot_download
+from huggingface_hub import file_exists, snapshot_download
 from packaging.version import parse
 
 from kernels.lockfile import KernelLock, VariantLock
 
-CACHE_DIR: Optional[str] = os.environ.get("HF_KERNELS_CACHE", None)
+
+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 None:
-        raise AssertionError(
-            "This kernel requires CUDA to be installed. Torch was not compiled with CUDA enabled."
-        )
+    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__)
-    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}"
+    return f"torch{torch_version.major}{torch_version.minor}-{cxxabi}-{compute_framework}-{cpu}-{os}"
 
 
 def universal_build_variant() -> str:
@@ -144,6 +161,29 @@ def get_kernel(repo_id: str, revision: str = "main") -> ModuleType:
     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.

tests/test_basic.py

@@ -1,7 +1,7 @@
 import pytest
 import torch
 
-from kernels import get_kernel
+from kernels import get_kernel, has_kernel
 
 
 @pytest.fixture
@@ -36,6 +36,22 @@ 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")

tests/test_layer.py

@@ -0,0 +1,314 @@
+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",
+        )
+    },
+    "SiluAndMulNoCompile": {
+        "cuda": LayerRepository(
+            repo_id="kernels-test/op-without-fake-test",
+            layer_name="SiluAndMul",
+        )
+    },
+    "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("SiluAndMulNoCompile")
+class SiluAndMulNoCompileKernel(SiluAndMul):
+    pass
+
+
+@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()
+
+
+@pytest.mark.parametrize("cls", [SiluAndMulWithKernel, SiluAndMulNoCompileKernel])
+@pytest.mark.parametrize("device", ["cuda", "cpu"])
+def test_torch_compile_layer(cls, device):
+    silu_and_mul = SiluAndMul()
+
+    X = torch.randn((32, 64), dtype=torch.float32, device=device)
+    Y = silu_and_mul(X)
+
+    silu_and_mul_with_kernel = cls()
+    silu_and_mul_with_kernel.eval()
+    silu_and_mul_compiled = torch.compile(silu_and_mul_with_kernel)
+
+    Y_compiled = silu_and_mul_compiled(X)
+
+    torch.testing.assert_close(Y_compiled, Y)
+
+
+def test_mapping_contexts():
+    assert set(_KERNEL_MAPPING.get().keys()) == {
+        "SiluAndMul",
+        "SiluAndMulStringDevice",
+        "SiluAndMulNoCompile",
+    }
+
+    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",
+            "SiluAndMulNoCompile",
+            "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",
+                "SiluAndMulNoCompile",
+                "TestKernel",
+            }
+            assert (
+                _KERNEL_MAPPING.get()["SiluAndMul"][Device(type="cuda")].repo_id
+                == "kernels-community/non-existing"
+            )
+
+        assert set(_KERNEL_MAPPING.get().keys()) == {
+            "SiluAndMul",
+            "SiluAndMulStringDevice",
+            "SiluAndMulNoCompile",
+            "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",
+            "SiluAndMulNoCompile",
+            "TestKernel",
+        }
+        assert (
+            _KERNEL_MAPPING.get()["SiluAndMul"][Device(type="cuda")].repo_id
+            == "kernels-community/activation"
+        )
+
+    assert set(_KERNEL_MAPPING.get().keys()) == {
+        "SiluAndMul",
+        "SiluAndMulStringDevice",
+        "SiluAndMulNoCompile",
+    }
+
+
+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