# XNNPACK Backend

[XNNPACK](https://github.com/google/XNNPACK) is a library of optimized neural network operators for ARM and x86 CPU platforms. Our delegate lowers models to run using these highly optimized CPU operators. You can try out lowering and running some example models in the demo. Please refer to the following docs for information on the XNNPACK Delegate
- [XNNPACK Backend Delegate Overview](https://pytorch.org/executorch/stable/native-delegates-executorch-xnnpack-delegate.html)
- [XNNPACK Delegate Export Tutorial](https://pytorch.org/executorch/stable/tutorial-xnnpack-delegate-lowering.html)


## Directory structure

```bash
examples/xnnpack
├── quantization                      # Scripts to illustrate PyTorch 2 Export Quantization workflow with XNNPACKQuantizer
│   └── example.py
├── aot_compiler.py                   # The main script to illustrate the full AOT (export, quantization, delegation) workflow with XNNPACK delegate
└── README.md                         # This file
```

## Delegating a Floating-point Model

The following command will produce a floating-point XNNPACK delegated model `mv2_xnnpack_fp32.pte` that can be run using XNNPACK's operators. It will also print out the lowered graph, showing what parts of the models have been lowered to XNNPACK via `executorch_call_delegate`.

```bash
# For MobileNet V2
python3 -m examples.xnnpack.aot_compiler --model_name="mv2" --delegate
```

Once we have the model binary (pte) file, then let's run it with ExecuTorch runtime using the `xnn_executor_runner`. With cmake, you first configure your cmake with the following:

```bash
# cd to the root of executorch repo
cd executorch

# Get a clean cmake-out directory
rm -rf cmake-out
mkdir cmake-out

# Configure cmake
cmake \
    -DCMAKE_INSTALL_PREFIX=cmake-out \
    -DCMAKE_BUILD_TYPE=Release \
    -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
    -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
    -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON \
    -DEXECUTORCH_BUILD_XNNPACK=ON \
    -DEXECUTORCH_ENABLE_LOGGING=ON \
    -DPYTHON_EXECUTABLE=python \
    -Bcmake-out .
```

Then you can build the runtime components with

```bash
cmake --build cmake-out -j9 --target install --config Release
```

Now finally you should be able to run this model with the following command

```bash
./cmake-out/backends/xnnpack/xnn_executor_runner --model_path ./mv2_xnnpack_fp32.pte
```

## Quantization
First, learn more about the generic PyTorch 2 Export Quantization workflow in the [Quantization Flow Docs](https://pytorch.org/executorch/stable/quantization-overview.html), if you are not familiar already.

Here we will discuss quantizing a model suitable for XNNPACK delegation using XNNPACKQuantizer.

Though it is typical to run this quantized mode via XNNPACK delegate, we want to highlight that this is just another quantization flavor, and we can run this quantized model without necessarily using XNNPACK delegate, but only using standard quantization operators.

A shared library to register the out variants of the quantized operators (e.g., `quantized_decomposed::add.out`) into EXIR is required. On cmake, follow the instructions in `test_quantize.sh` to build it, the default path is `cmake-out/kernels/quantized/libquantized_ops_lib.so`.

Then you can generate a XNNPACK quantized model with the following command by passing the path to the shared library into the script `quantization/example.py`:
```bash
python3 -m examples.xnnpack.quantization.example --model_name "mv2" --so_library "<path/to/so/lib>" # for MobileNetv2

# This should generate ./mv2_quantized.pte file, if successful.
```
You can find more valid quantized example models by running:
```bash
python3 -m examples.xnnpack.quantization.example --help
```

## Running the XNNPACK Model with CMake
After exporting the XNNPACK Delegated model, we can now try running it with example inputs using CMake. We can build and use the xnn_executor_runner, which is a sample wrapper for the ExecuTorch Runtime and XNNPACK Backend. We first begin by configuring the CMake build like such:
```bash
# cd to the root of executorch repo
cd executorch

# Get a clean cmake-out directory
rm -rf cmake-out
mkdir cmake-out

# Configure cmake
cmake \
    -DCMAKE_INSTALL_PREFIX=cmake-out \
    -DCMAKE_BUILD_TYPE=Release \
    -DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
    -DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
    -DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON \
    -DEXECUTORCH_BUILD_XNNPACK=ON \
    -DEXECUTORCH_ENABLE_LOGGING=ON \
    -DPYTHON_EXECUTABLE=python \
    -Bcmake-out .
```
Then you can build the runtime componenets with

```bash
cmake --build cmake-out -j9 --target install --config Release
```

Now you should be able to find the executable built at `./cmake-out/backends/xnnpack/xnn_executor_runner` you can run the executable with the model you generated as such
```bash
./cmake-out/backends/xnnpack/xnn_executor_runner --model_path=./mv2_quantized.pte
```

## Delegating a Quantized Model

The following command will produce a XNNPACK quantized and delegated model `mv2_xnnpack_q8.pte` that can be run using XNNPACK's operators. It will also print out the lowered graph, showing what parts of the models have been lowered to XNNPACK via `executorch_call_delegate`.

```bash
python3 -m examples.xnnpack.aot_compiler --model_name "mv2" --quantize --delegate
```