# Quantization

🤗 Optimum provides an `optimum.onnxruntime` package that enables you to apply quantization on many models hosted on
the Hugging Face Hub using the [ONNX Runtime](https://github.com/microsoft/onnxruntime/blob/master/onnxruntime/python/tools/quantization/README.md)
quantization tool.

The quantization process is abstracted via the [ORTConfig](/docs/optimum/main/en/onnxruntime/package_reference/configuration#optimum.onnxruntime.ORTConfig) and
the [ORTQuantizer](/docs/optimum/main/en/onnxruntime/package_reference/quantization#optimum.onnxruntime.ORTQuantizer) classes. The former allows you to specify how quantization should be done,
while the latter effectively handles quantization.

<Tip>

You can read the [conceptual guide on quantization](../../concept_guides/quantization) to learn about quantization. It
explains the main concepts that you will be using when performing quantization with the
[ORTQuantizer](/docs/optimum/main/en/onnxruntime/package_reference/quantization#optimum.onnxruntime.ORTQuantizer).

</Tip>

## Quantizing a model to be used with Optimum's CLI

The Optimum ONNX Runtime quantization tool can be used through Optimum command-line interface:

```bash
optimum-cli onnxruntime quantize --help
usage: optimum-cli <command> [<args>] onnxruntime quantize [-h] --onnx_model ONNX_MODEL -o OUTPUT [--per_channel] (--arm64 | --avx2 | --avx512 | --avx512_vnni | --tensorrt | -c CONFIG)

options:
  -h, --help            show this help message and exit
  --arm64               Quantization for the ARM64 architecture.
  --avx2                Quantization with AVX-2 instructions.
  --avx512              Quantization with AVX-512 instructions.
  --avx512_vnni         Quantization with AVX-512 and VNNI instructions.
  --tensorrt            Quantization for NVIDIA TensorRT optimizer.
  -c CONFIG, --config CONFIG
                        `ORTConfig` file to use to optimize the model.

Required arguments:
  --onnx_model ONNX_MODEL
                        Path to the repository where the ONNX models to quantize are located.
  -o OUTPUT, --output OUTPUT
                        Path to the directory where to store generated ONNX model.

Optional arguments:
  --per_channel         Compute the quantization parameters on a per-channel basis.

```

Quantizing an ONNX model can be done as follows:

```bash
 optimum-cli onnxruntime quantize --onnx_model onnx_model_location/ --avx512 -o quantized_model/
```

This quantize all the ONNX files in `onnx_model_location` with the AVX-512 instructions.

## Creating an `ORTQuantizer`

The [ORTQuantizer](/docs/optimum/main/en/onnxruntime/package_reference/quantization#optimum.onnxruntime.ORTQuantizer) class is used to quantize your ONNX model. The class can be initialized using
the `from_pretrained()` method, which supports different checkpoint formats.

1. Using an already initialized `ORTModelForXXX` class.

```python
>>> from optimum.onnxruntime import ORTQuantizer, ORTModelForSequenceClassification

# Loading ONNX Model from the Hub
>>> ort_model = ORTModelForSequenceClassification.from_pretrained(
...     "optimum/distilbert-base-uncased-finetuned-sst-2-english"
... )

# Create a quantizer from a ORTModelForXXX
>>> quantizer = ORTQuantizer.from_pretrained(ort_model)
```

2. Using a local ONNX model from a directory.

```python
>>> from optimum.onnxruntime import ORTQuantizer

# This assumes a model.onnx exists in path/to/model
>>> quantizer = ORTQuantizer.from_pretrained("path/to/model")
```


## Apply Dynamic Quantization

The [ORTQuantizer](/docs/optimum/main/en/onnxruntime/package_reference/quantization#optimum.onnxruntime.ORTQuantizer) class can be used to quantize dynamically your ONNX model. Below you will
find an easy end-to-end example on how to quantize dynamically
[distilbert-base-uncased-finetuned-sst-2-english](https://huggingface.co/distilbert-base-uncased-finetuned-sst-2-english).

```python
>>> from optimum.onnxruntime import ORTQuantizer, ORTModelForSequenceClassification
>>> from optimum.onnxruntime.configuration import AutoQuantizationConfig

# Load PyTorch model and convert to ONNX
>>> onnx_model = ORTModelForSequenceClassification.from_pretrained("distilbert-base-uncased-finetuned-sst-2-english", export=True)

# Create quantizer
>>> quantizer = ORTQuantizer.from_pretrained(onnx_model)

# Define the quantization strategy by creating the appropriate configuration
>>> dqconfig = AutoQuantizationConfig.avx512_vnni(is_static=False, per_channel=False)

# Quantize the model
>>> model_quantized_path = quantizer.quantize(
...     save_dir="path/to/output/model",
...     quantization_config=dqconfig,
... )
```

## Static Quantization example

The [ORTQuantizer](/docs/optimum/main/en/onnxruntime/package_reference/quantization#optimum.onnxruntime.ORTQuantizer) class can be used to quantize statically your ONNX model. Below you will find
an easy end-to-end example on how to quantize statically
[distilbert-base-uncased-finetuned-sst-2-english](https://huggingface.co/distilbert-base-uncased-finetuned-sst-2-english).

```python
>>> from functools import partial
>>> from transformers import AutoTokenizer
>>> from optimum.onnxruntime import ORTQuantizer, ORTModelForSequenceClassification
>>> from optimum.onnxruntime.configuration import AutoQuantizationConfig, AutoCalibrationConfig

>>> model_id = "distilbert-base-uncased-finetuned-sst-2-english"

# Load PyTorch model and convert to ONNX and create Quantizer and setup config
>>> onnx_model = ORTModelForSequenceClassification.from_pretrained(model_id, export=True)
>>> tokenizer = AutoTokenizer.from_pretrained(model_id)
>>> quantizer = ORTQuantizer.from_pretrained(onnx_model)
>>> qconfig = AutoQuantizationConfig.arm64(is_static=True, per_channel=False)

# Create the calibration dataset
>>> def preprocess_fn(ex, tokenizer):
...     return tokenizer(ex["sentence"])

>>> calibration_dataset = quantizer.get_calibration_dataset(
...     "glue",
...     dataset_config_name="sst2",
...     preprocess_function=partial(preprocess_fn, tokenizer=tokenizer),
...     num_samples=50,
...     dataset_split="train",
... )

# Create the calibration configuration containing the parameters related to calibration.
>>> calibration_config = AutoCalibrationConfig.minmax(calibration_dataset)

# Perform the calibration step: computes the activations quantization ranges
>>> ranges = quantizer.fit(
...     dataset=calibration_dataset,
...     calibration_config=calibration_config,
...     operators_to_quantize=qconfig.operators_to_quantize,
... )

# Apply static quantization on the model
>>> model_quantized_path = quantizer.quantize(
...     save_dir="path/to/output/model",
...     calibration_tensors_range=ranges,
...     quantization_config=qconfig,
... )
```

## Quantize Seq2Seq models

The [ORTQuantizer](/docs/optimum/main/en/onnxruntime/package_reference/quantization#optimum.onnxruntime.ORTQuantizer) class currently doesn't support multi-file models, like
[ORTModelForSeq2SeqLM](/docs/optimum/main/en/onnxruntime/package_reference/modeling#optimum.onnxruntime.ORTModelForSeq2SeqLM). If you want to quantize a Seq2Seq model, you have to quantize each
model's component individually.

<Tip warning={true}>

Currently, only dynamic quantization is supported for Seq2Seq models.

</Tip>

1. Load seq2seq model as `ORTModelForSeq2SeqLM`.

```python
>>> from optimum.onnxruntime import ORTQuantizer, ORTModelForSeq2SeqLM
>>> from optimum.onnxruntime.configuration import AutoQuantizationConfig

# load Seq2Seq model and set model file directory
>>> model_id = "optimum/t5-small"
>>> onnx_model = ORTModelForSeq2SeqLM.from_pretrained(model_id)
>>> model_dir = onnx_model.model_save_dir
```

2. Define Quantizer for encoder, decoder and decoder with past keys

```python
# Create encoder quantizer
>>> encoder_quantizer = ORTQuantizer.from_pretrained(model_dir, file_name="encoder_model.onnx")

# Create decoder quantizer
>>> decoder_quantizer = ORTQuantizer.from_pretrained(model_dir, file_name="decoder_model.onnx")

# Create decoder with past key values quantizer
>>> decoder_wp_quantizer = ORTQuantizer.from_pretrained(model_dir, file_name="decoder_with_past_model.onnx")

# Create Quantizer list
>>> quantizer = [encoder_quantizer, decoder_quantizer, decoder_wp_quantizer]
```

3. Quantize all models

```python
# Define the quantization strategy by creating the appropriate configuration
>>> dqconfig = AutoQuantizationConfig.avx512_vnni(is_static=False, per_channel=False)

# Quantize the models individually
>>> for q in quantizer:
...     q.quantize(save_dir=".",quantization_config=dqconfig)  # doctest: +IGNORE_RESULT
```