---
title: "Ascend NPU Operator Development Guide"
description: "How to develop custom operators (Ascend C / Triton) for Ascend NPU and integrate them into the SGLang inference engine."
---

## Overview

[SGL-Kernel-NPU](https://github.com/sgl-project/sgl-kernel-npu) is the official
operator library provided by the SGLang framework for Ascend NPU. It includes
two types of operator implementations:

1. **Ascend C operators**: High-performance C++ kernels written in Ascend C,
   compiled into `libsgl_kernel_npu.so`, and registered through PyTorch's custom
   operator mechanism (`TORCH_LIBRARY_FRAGMENT`). Called in SGLang via
   `torch.ops.npu.<op_name>()`.
2. **Triton operators**: Python kernels written in Triton, adapted for Ascend
   NPU. Called directly via `from sgl_kernel_npu.xxx import ...`.

When SGLang detects an NPU device, it automatically loads `sgl_kernel_npu` and
uses its operators in place of GPU counterparts, providing optimized inference
on Ascend hardware.

## Directory Structure

<Note>
The identifiers `sgl_kenel_npu_ops.h`, `KernalHelloworld`, and `retrive_*` (e.g., `retrive_index`,
`retrive_next_token`, `retrive_next_sibling`) in this guide match the spelling used in the
upstream [sgl-kernel-npu](https://github.com/sgl-project/sgl-kernel-npu) repository and are kept verbatim for consistency.
</Note>

```text
sgl-kernel-npu/
├── csrc/                          # Ascend C operator C++ sources
│   ├── CMakeLists.txt             # Build configuration
│   ├── pytorch_extensions.cpp     # PyTorch op registration (core integration file)
│   └── <op_name>/                 # One directory per operator
│       ├── op_host/               # Host-side code (validation, tiling, launch)
│       │   ├── <op_name>.cpp
│       │   └── tiling/            # Optional: tiling data
│       └── op_kernel/             # Device-side code (Ascend C kernel on AICore)
│           └── <op_name>_kernel.cpp
├── include/
│   └── sgl_kenel_npu_ops.h        # C++ interface declarations
├── python/
│   └── sgl_kernel_npu/
│       └── sgl_kernel_npu/
│           ├── __init__.py        # Loads libsgl_kernel_npu.so
│           ├── attention/         # Triton attention kernels
│           ├── norm/              # Triton normalization kernels
│           ├── activation/        # Triton activation kernels
│           ├── fla/               # Triton linear attention kernels
│           ├── mamba/             # Triton Mamba kernels
│           ├── moe/               # Triton MoE kernels
│           └── sample/            # Triton speculative decoding kernels
├── tests/
│   └── python/sgl_kernel_npu/     # One test file per operator
├── build.sh                       # Build script
└── CMakeLists.txt                 # Root CMake configuration
```

## Developing Ascend C Operators

A complete Ascend C operator consists of two parts:

- **Device part**: Kernel code running on the NPU AICore, responsible for actual
  computation. Written using the Ascend C API.
- **Host part**: Code running on the CPU, responsible for parameter validation,
  data pre-processing, tiling, and kernel launch.

We recommend starting with the
[helloworld](https://github.com/sgl-project/sgl-kernel-npu/tree/main/csrc/helloworld)
example, a simple operator that performs element-wise addition on two tensors.

### Step 1: Create the operator directory and files

Create a new operator directory under `csrc/`, following the `op_host/` +
`op_kernel/` structure:

```text
csrc/<op_name>/
├── op_host/
│   └── <op_name>.cpp
└── op_kernel/
    └── <op_name>_kernel.cpp
```

### Step 2: Write the Device-side Kernel (op_kernel)

Device-side code runs on AICore and follows the Ascend C programming model. The
core structure is a class with `Init()` and `Process()` methods, plus an
`extern "C"` entry function.

Using helloworld as an example:

```cpp
// csrc/helloworld/op_kernel/kernel_helloworld.cpp
#include "kernel_operator.h"

constexpr int32_t BUFFER_NUM = 2;

class KernalHelloworld {
public:
    __aicore__ inline KernalHelloworld() {}

    __aicore__ inline void Init(GM_ADDR x, GM_ADDR y, GM_ADDR z, uint32_t totalLength)
    {
        // Compute workload for current block
        this->blockLength = totalLength / AscendC::GetBlockNum();
        this->tileNum = 8;
        this->tileLength = this->blockLength / this->tileNum / BUFFER_NUM;

        // Set global memory buffers
        xGm.SetGlobalBuffer((__gm__ half *)x + this->blockLength * AscendC::GetBlockIdx(), this->blockLength);
        yGm.SetGlobalBuffer((__gm__ half *)y + this->blockLength * AscendC::GetBlockIdx(), this->blockLength);
        zGm.SetGlobalBuffer((__gm__ half *)z + this->blockLength * AscendC::GetBlockIdx(), this->blockLength);

        // Initialize pipeline queues
        pipe.InitBuffer(inQueueX, BUFFER_NUM, this->tileLength * sizeof(half));
        pipe.InitBuffer(inQueueY, BUFFER_NUM, this->tileLength * sizeof(half));
        pipe.InitBuffer(outQueueZ, BUFFER_NUM, this->tileLength * sizeof(half));
    }

    __aicore__ inline void Process()
    {
        int32_t loopCount = this->tileNum * BUFFER_NUM;
        for (int32_t i = 0; i < loopCount; i++) {
            CopyIn(i);    // Move data from Global Memory to Local Memory
            Compute(i);   // Compute on Local Memory
            CopyOut(i);   // Move results back to Global Memory
        }
    }

private:
    __aicore__ inline void CopyIn(int32_t progress) { /* data copy-in... */ }
    __aicore__ inline void Compute(int32_t progress) { /* core computation... */ }
    __aicore__ inline void CopyOut(int32_t progress) { /* data copy-out... */ }

private:
    AscendC::TPipe pipe;
    AscendC::TQue<AscendC::TPosition::VECIN, BUFFER_NUM> inQueueX, inQueueY;
    AscendC::TQue<AscendC::TPosition::VECOUT, BUFFER_NUM> outQueueZ;
    AscendC::GlobalTensor<half> xGm, yGm, zGm;
    uint32_t blockLength, tileNum, tileLength;
};

// Entry function: the compile tool auto-generates aclrtlaunch_<op_name>.h from this name
extern "C" __global__ __aicore__ void helloworld(
    GM_ADDR x, GM_ADDR y, GM_ADDR z, uint32_t totalLength)
{
    KernalHelloworld op;
    op.Init(x, y, z, totalLength);
    op.Process();
}
```

**Key points:**

- Class methods must be marked with `__aicore__`, indicating they run on AICore.
- Use `AscendC::TPipe` + `AscendC::TQue` to build a pipeline that overlaps data
  movement and computation.
- The entry function must be declared `extern "C" __global__ __aicore__`. The
  compile tool generates a host-callable launch header
  `aclrtlaunch_<func_name>.h` from the function name.
- Simple operators (e.g., helloworld, cache_assign, lora) do not need extra
  workspace memory. Complex operators (e.g., mla_preprocess, alloc_extend,
  build_tree) require temporary workspace memory and are compiled separately in
  `CMakeLists.txt`.

For more in-depth Ascend C programming knowledge, refer to the
[Ascend C Kernel Development Guide](https://www.hiascend.com/document/detail/zh/CANNCommunityEdition/850alpha001/opdevg/Ascendcopdevg/atlas_ascendc_10_0001.html).

### Step 3: Write the Host-side Code (op_host)

Host-side code is responsible for passing PyTorch Tensors to the kernel and
launching it. The key macro is `EXEC_KERNEL_CMD` (located in
`csrc/utils/torch_helper.h`).

```cpp
// csrc/helloworld/op_host/helloworld.cpp
#include "defines.h"                   // Provides HOST_API macro
#include "torch_helper.h"              // Provides EXEC_KERNEL_CMD macro
#include "aclrtlaunch_helloworld.h"    // Auto-generated by compile tool

namespace sglang {
namespace npu_kernel {

HOST_API at::Tensor helloworld(const at::Tensor &x, const at::Tensor &y)
{
    // Create output tensor
    at::Tensor z = at::empty_like(x);

    // Define block count
    uint32_t blockDim = 8;

    // Compute total element count
    uint32_t totalLength = 1;
    for (uint32_t size : x.sizes()) {
        totalLength *= size;
    }

    // Launch kernel via EXEC_KERNEL_CMD macro
    EXEC_KERNEL_CMD(helloworld, blockDim, x, y, z, totalLength);
    return z;
}

} // namespace npu_kernel
} // namespace sglang
```

**Key points:**

- The namespace must be `sglang::npu_kernel`.
- Function signatures follow the pattern
  `at::Tensor <op_name>(const at::Tensor &input, ...)`.
- For operators with multiple outputs, use
  `std::tuple<at::Tensor, at::Tensor, ...>` or non-const reference parameters.

### Step 4: Declare the C++ Interface (include/sgl_kenel_npu_ops.h)

Add the operator function declaration in `include/sgl_kenel_npu_ops.h`:

```cpp
// include/sgl_kenel_npu_ops.h
namespace sglang {
namespace npu_kernel {

at::Tensor helloworld(const at::Tensor &x, const at::Tensor &y);

} // namespace npu_kernel
} // namespace sglang
```

### Step 5: Register the PyTorch Custom Operator (pytorch_extensions.cpp)

Register the operator in `csrc/pytorch_extensions.cpp` in two steps: define the
schema and bind the implementation.

```cpp
// csrc/pytorch_extensions.cpp
namespace {

// 1. Define operator schema (used by torch.compile, etc.)
TORCH_LIBRARY_FRAGMENT(npu, m)
{
    m.def("helloworld(Tensor x, Tensor y) -> Tensor");
    // ... other operator schemas ...
}

// 2. Bind implementation for the PrivateUse1 device (i.e., NPU)
TORCH_LIBRARY_IMPL(npu, PrivateUse1, m)
{
    m.impl("helloworld", TORCH_FN(sglang::npu_kernel::helloworld));
    // ... other operator implementations ...
}

} // namespace
```

**Schema conventions:**

- The namespace is fixed to `npu`. In SGLang, operators are called via
  `torch.ops.npu.<op_name>()`.
- Output tensor parameters use the `Tensor(a!)` mutating annotation.
- Optional parameters use the `Tensor?` annotation, with `c10::optional<T>`
  handling in the impl.
- For detailed schema syntax, see the
  [PyTorch Schema Reference](https://github.com/pytorch/pytorch/blob/main/aten/src/ATen/native/README.md#func).

**Implementation binding rules:**

- The device name is fixed to `PrivateUse1` (PyTorch NPU backend identifier).
- Use the `TORCH_FN` macro to bind to the implementation function.
- For complex operators with optional parameters, use lambda expressions to
  unpack the arguments.

### Step 6: Update the Build Configuration (csrc/CMakeLists.txt)

Add the new operator's source files to `csrc/CMakeLists.txt`:

**For operators not requiring workspace** (simple operators), add kernel source
to `no_workspace_kernel`:

```cmake
ascendc_library(no_workspace_kernel STATIC
    # ... existing kernel files ...
    ${PROJECT_OP_SRC_BASE}/<op_name>/op_kernel/<op_name>_kernel.cpp
)
```

**For operators requiring workspace** (complex operators), add kernel source to
`workspace_kernel` with the `-DHAVE_WORKSPACE -DHAVE_TILING` compile flags:

```cmake
ascendc_library(workspace_kernel STATIC
    # ... existing kernel files ...
    ${PROJECT_OP_SRC_BASE}/<op_name>/op_kernel/<op_name>_kernel.cpp
)
```

**Add host source files to `OP_SRCS`:**

```cmake
FILE(GLOB OP_SRCS
    # ... existing host files ...
    ${PROJECT_OP_SRC_BASE}/<op_name>/op_host/<op_name>.cpp
)
```

### Step 7: Build

Build following the steps in the
[python/sgl_kernel_npu/README.md](https://github.com/sgl-project/sgl-kernel-npu/blob/main/python/sgl_kernel_npu/README.md):

```bash
cd sgl-kernel-npu

# Build all modules
bash build.sh

# Install the sgl_kernel_npu wheel
pip install output/sgl_kernel_npu*.whl
```

The compiled `libsgl_kernel_npu.so` is copied into
`python/sgl_kernel_npu/sgl_kernel_npu/lib/` and loaded by the Python package.

## Developing Triton Operators

Triton operators are located under `python/sgl_kernel_npu/sgl_kernel_npu/`,
organized by function category:

```text
python/sgl_kernel_npu/sgl_kernel_npu/
├── attention/     # Attention (decode_attention, sinks_attention)
├── norm/          # Normalization (rmsnorm, fused_qk_norm, l1_norm)
├── activation/    # Activation (swiglu_oai, swiglu_quant)
├── fla/           # Linear attention (chunk, cumsum, wy_fast)
├── mamba/         # Mamba-related (causal_conv1d, state_update)
├── moe/           # MoE-related (mul_add, zero_experts)
└── sample/        # Speculative decoding (verify_tree_greedy)
```

**Development steps:**

1. Create a new `.py` file in the appropriate category subdirectory.
2. Write the kernel using the Triton language, using existing operators in the
   same directory as templates.
3. Export functions in the corresponding `__init__.py` if needed.
4. Write tests under `tests/python/sgl_kernel_npu/`.

**Note:** Many Triton operators are adapted from SGLang's GPU Triton kernels
(e.g., comments in `fla/utils.py` note the original source). Pay special
attention to differences between NPU and GPU when adapting.

## Integrating Operators into SGLang

### Ascend C Operator Integration

After completing the [Steps 1-7](#developing-ascend-c-operators) above (writing
the kernel, registering the torch op, building), and installing the
`sgl-kernel-npu` wheel, call the operator in SGLang as follows:

```python
import sgl_kernel_npu  # Loading the library auto-triggers libsgl_kernel_npu.so loading

# Call the operator
result = torch.ops.npu.helloworld(x, y)
```

Real-world usage in SGLang (from `sglang/srt/speculative/eagle_utils.py`):

```python
torch.ops.npu.build_tree_kernel_efficient(
    parent_list, selected_index, verified_seq_len, tree_mask,
    positions, retrive_index, retrive_next_token,
    retrive_next_sibling, topk, depth, draft_token_num, tree_mask_mode
)
```

### Triton Operator Integration

Import and call directly via Python:

```python
from sgl_kernel_npu.attention.decode_attention import decode_attention_fwd
from sgl_kernel_npu.norm.rmsnorm_bias import rmsnorm_bias
from sgl_kernel_npu.mamba.causal_conv1d import causal_conv1d_fwd

# Direct function call
output = decode_attention_fwd(q, k, v, ...)
```

Real-world usage in SGLang (from `sglang/srt/models/llama.py`):

```python
from sgl_kernel_npu.norm.split_qkv_rmsnorm_rope import split_qkv_rmsnorm_rope
```

### sgl-kernel-npu Wheel Update Process

Since SGLang and sgl-kernel-npu are separate Python packages, dependency updates
require a multi-PR workflow:

1. **Submit sgl-kernel-npu PR**: Add/modify operators in the sgl-kernel-npu
   repository, ensuring all tests pass.
2. **Bump sgl-kernel-npu version**: Update the version number in sgl-kernel-npu.
   Merging triggers an automatic PyPI release.
3. **Reference the new version in SGLang**:
   - Update the `sgl-kernel-npu` version requirement in SGLang's
     `python/pyproject.toml`.
   - Use the new operator in SGLang code.

If not urgent, you can wait for a regular release (typically within one week).

## Writing Unit Tests

Each operator needs a corresponding unit test under
`tests/python/sgl_kernel_npu/`, using Python's `unittest` framework.

Test file naming convention: `test_<op_name>.py`

```python
# tests/python/sgl_kernel_npu/test_helloworld.py
import unittest
import torch
import sgl_kernel_npu

class TestHelloworld(unittest.TestCase):
    def test_helloworld_basic(self):
        x = torch.randn(2048, dtype=torch.float16, device="npu")
        y = torch.randn(2048, dtype=torch.float16, device="npu")

        z = torch.ops.npu.helloworld(x, y)
        expected = x + y

        torch.testing.assert_close(z, expected)

if __name__ == "__main__":
    unittest.main()
```

Run tests:

```bash
python tests/python/sgl_kernel_npu/test_helloworld.py
```

**Testing checklist:**

- Cover typical input shapes (power-of-2 sizes and non-standard sizes).
- Cover different data types (bf16 / fp16, etc.).
- For operators with in-place behavior, verify correctness of output tensors.
- Compare against PyTorch native computation to verify accuracy.

## Code Style

### Pre-commit Checks

sgl-kernel-npu uses pre-commit for consistent code style:

```bash
pip3 install pre-commit
cd sgl-kernel-npu
pre-commit install
pre-commit run --all-files
```

**Note:** If `pre-commit run --all-files` fails the first time, run it again to
ensure all lint errors are auto-fixed. All code must pass checks before
submitting a PR.

### C++ Code Style

- Use the C++17 standard.
- Place all operator implementations under the `sglang::npu_kernel` namespace.
- Follow existing code style; format using `.clang-format`.
- Use `TORCH_CHECK` for error checking (not the standard GE `OP_ADD` macros).
- Do not include unnecessary GE registration code (e.g., `OP_ADD()` macros).

### Python Code Style

- Follow PEP 8.
- Use snake_case for file and function names.
- When adapting from SGLang GPU code, note the original source in the file
  header.

### General Principles

- Avoid code duplication: extract shared functions for any repeated code blocks
  over 5 lines.
- Minimize device synchronization: reduce CPU-NPU sync operations like
  `tensor.item()` or `tensor.cpu()`.
- Keep functions pure: avoid in-place argument modification.
- Keep files concise: split files exceeding 2,000 lines.

## Submitting a PR

1. **Fork the repo**: Fork
   [sgl-kernel-npu](https://github.com/sgl-project/sgl-kernel-npu) on GitHub,
   then clone locally.
2. **Create a branch**: Create a new branch from `main`, e.g.,
   `feature/add-my-op`.
3. **Develop and test**: Develop the operator and write tests following the
   steps above. Ensure all tests pass.
4. **Run pre-commit**: Ensure code formatting compliance.
5. **Commit and push**:

   ```bash
   git add .
   git commit -m "feat: add <op_name> operator"
   git push origin feature/add-my-op
   ```

6. **Create a PR**: Open a Pull Request on GitHub from your branch to
   `sgl-project/sgl-kernel-npu:main`.
7. **Wait for CI and review**: CI checks include linting, compilation, and
   operator tests. After passing, wait for maintainer review and merge.

## References

- [SGL-Kernel-NPU Official Repository](https://github.com/sgl-project/sgl-kernel-npu)
- [SGL-Kernel-NPU Contribution Guide](https://github.com/sgl-project/sgl-kernel-npu/blob/main/docs/developer_guide/contribution_guide.md)
- [Ascend C Kernel Development Guide](https://www.hiascend.com/document/detail/zh/CANNCommunityEdition/850alpha001/opdevg/Ascendcopdevg/atlas_ascendc_10_0001.html)
- [PyTorch Custom Ops Schema Reference](https://github.com/pytorch/pytorch/blob/main/aten/src/ATen/native/README.md#func)
- [helloworld Example Operator](https://github.com/sgl-project/sgl-kernel-npu/tree/main/csrc/helloworld)
- [SGLang Contribution Guide](/docs/hardware-platforms/ascend-npus/ascend_contribution_guide)
