| --- |
| library_name: kernels |
| license: apache-2.0 |
| tags: |
| - kernel |
| - webgpu |
| - wgsl |
| --- |
| # com.microsoft.MatMulBnb4 |
|
|
| `com.microsoft` · ONNX Runtime contrib operator · contrib since_version 1 |
| |
| ## Description |
| |
| Computes `A @ dequant(B)^T` where `B` uses bitsandbytes 4-bit quantization: `quant_type = 0` selects FP4 and `quant_type = 1` selects NF4. Supports rank-2 float16/float32 `A`, `transB = 1`, and `training_mode = 0`; rank-1 and rank-3-or-higher `A`, bfloat16, `transB = 0`, and training are not implemented. `B` is the flattened `[N, K]` weight, two codes per byte with the even flat index in the high nibble. Each code indexes a fixed 16-entry codebook, and the value is `codebook[code] * absmax[flat_index / block_size]`. |
|
|
| See the [ONNX Runtime `MatMulBnb4` contrib-operator spec](https://github.com/microsoft/onnxruntime/blob/main/docs/ContribOperators.md#com.microsoft.MatMulBnb4) for the reference semantics. |
|
|
| ## Inputs |
|
|
| | Name | Bind key | Logical dtype | Rank | Shape | Description | Presence | |
| | --- | --- | --- | --- | --- | --- | --- | |
| | `A` | `aT` | `T1` | `2` | — | Float input matrix of shape `(M, K)`, not quantized. | required | |
| | `B` | `bT` | `T2` | `1` | — | The `[N, K]` weight, flattened and quantized to 4 bits, stored as `(N * K + 1) / 2` bytes; the ONNX type is uint8 (this WebGPU implementation reads one widened u32 per stored byte). | required | |
| | `absmax` | `absmaxT` | `T1` | `1` | — | Per-block absolute-maximum dequantization scales of shape `((N * K + block_size - 1) / block_size)`, same dtype as A. | required | |
|
|
| ## Outputs |
|
|
| | Name | Bind key | Logical dtype | Rank | Shape | Description | Presence | |
| | --- | --- | --- | --- | --- | --- | --- | |
| | `Y` | `yT` | `T1` | `2` | `[A[0], N]` | Result of `A` multiplied by the dequantized, transposed weight matrix, with shape `(M, N)` and the same dtype as `A`. | required | |
|
|
| ## Attributes |
|
|
| Attributes and default values (overridable per request): |
|
|
| | Attribute | Default | Description | |
| | --- | --- | --- | |
| | `training_mode` | `0` | Whether training outputs are requested. This inference-only implementation supports the standard default value 0. | |
| | `transB` | `1` | Whether the quantized weight is stored transposed. This implementation supports the standard default value 1. | |
| | `K` | — | Input feature count (the shared dimension). | |
| | `N` | — | Output feature count. | |
| | `block_size` | — | Number of weights sharing one absmax scale; a power of two, at least 16. | |
| | `quant_type` | — | Codebook selector: 0 = FP4, 1 = NF4. | |
|
|
| ## Type constraints |
|
|
| | Variable | Allowed dtypes | |
| | --- | --- | |
| | `T1` | `float32`, `float16` | |
| | `T2` | `uint8` | |
|
|
| ## Device requirements |
|
|
| Some implementation variants require `subgroup-matrix` and `subgroups`. These are route-specific capabilities, not package-wide requirements; availability also depends on the request shape and dtype. |
|
|
| ## Files |
|
|
| - [`metadata.json`](build/webgpu/metadata.json) — kernel metadata (id, digests, provenance) |
| - [`manifest.json`](build/webgpu/manifest.json) — the op contract (source of truth) |
| - [`test.json`](build/webgpu/test.json) — correctness cases |
| - [`bench.json`](build/webgpu/bench.json) — benchmark + tuning cases |
| - [`cast-scalar-x4.wgsl.jinja`](build/webgpu/cast-scalar-x4.wgsl.jinja) |
| - [`matmul-bnb4-gemv.wgsl.jinja`](build/webgpu/matmul-bnb4-gemv.wgsl.jinja) |
| - [`matmul-bnb4-sgmat.wgsl.jinja`](build/webgpu/matmul-bnb4-sgmat.wgsl.jinja) |
| - [`matmul-bnb4-tiled.wgsl.jinja`](build/webgpu/matmul-bnb4-tiled.wgsl.jinja) |
| - [`matmul-bnb4.wgsl.jinja`](build/webgpu/matmul-bnb4.wgsl.jinja) |
|
|
| ## Use with `@huggingface/kernels` |
|
|
| The loader derives every required output's shape and logical dtype from the manifest contract and this call. |
| It then allocates the result tensors automatically. |
|
|
| The `version: 1` option selects the published kernel contract; it is independent of any operator opset, contrib `since_version`, or model version. |
|
|
| Replace each `*Data` placeholder with a typed array containing the corresponding input data. |
|
|
| ```js |
| import { getKernel } from "@huggingface/kernels"; |
| |
| const kernel = await getKernel("webgpu-kernels/com.microsoft.MatMulBnb4", { version: 1 }); |
| const { yT } = await kernel({ |
| aT: { data: aTData, shape: [2, 24] }, |
| bT: { data: bTData, shape: [36] }, |
| absmaxT: { data: absmaxTData, shape: [5] }, |
| }, { |
| attrs: { |
| K: 24, |
| N: 3, |
| block_size: 16, |
| quant_type: 1, |
| }, |
| }); |
| ``` |
|
|
