.. meta::
   :description: How to use model quantization techniques to speed up inference.
   :keywords: ROCm, LLM, fine-tuning, usage, tutorial, quantization, Quark, GPTQ, transformers, bitsandbytes

*****************************
Model quantization techniques
*****************************

Quantization reduces the model size compared to its native full-precision version, making it easier to fit large models
onto GPUs with limited memory usage. This section explains how to perform LLM quantization using AMD Quark, GPTQ
and bitsandbytes on AMD Instinct hardware.

.. _quantize-llms-quark:

AMD Quark
=========

`AMD Quark <https://quark.docs.amd.com/latest/>`_ offers the leading efficient and scalable quantization solution tailored to AMD Instinct GPUs. It supports ``FP8`` and ``INT8`` quantization for activations, weights, and KV cache, 
including ``FP8`` attention. For very large models, it employs a two-level ``INT4-FP8`` scheme—storing weights in ``INT4`` while computing with ``FP8``—for nearly 4× compression without sacrificing accuracy. 
Quark scales efficiently across multiple GPUs, efficiently handling ultra-large models like Llama-3.1-405B. Quantized ``FP8`` models like Llama, Mixtral, and Grok-1 are available under the `AMD organization on Hugging Face <https://huggingface.co/collections/amd/quark-quantized-ocp-fp8-models-66db7936d18fcbaf95d4405c>`_, and can be deployed directly via `vLLM <https://github.com/vllm-project/vllm/tree/main/vllm>`_.

Installing Quark
-------------------

The latest release of Quark can be installed with pip

.. code-block:: shell

    pip install amd-quark

For detailed installation instructions, refer to the `Quark documentation <https://quark.docs.amd.com/latest/install.html>`_.


Using Quark for quantization
-----------------------------

#. First, load the pre-trained model and its corresponding tokenizer using the Hugging Face ``transformers`` library.

   .. code-block:: python

      from transformers import AutoTokenizer, AutoModelForCausalLM

      MODEL_ID = "meta-llama/Llama-2-70b-chat-hf"
      MAX_SEQ_LEN = 512

      model = AutoModelForCausalLM.from_pretrained(
          MODEL_ID, device_map="auto", torch_dtype="auto",
      )
      model.eval()

      tokenizer = AutoTokenizer.from_pretrained(MODEL_ID, model_max_length=MAX_SEQ_LEN)
      tokenizer.pad_token = tokenizer.eos_token

#. Prepare the calibration DataLoader (static quantization requires calibration data).

   .. code-block:: python

      from datasets import load_dataset
      from torch.utils.data import DataLoader

      BATCH_SIZE = 1
      NUM_CALIBRATION_DATA = 512

      dataset = load_dataset("mit-han-lab/pile-val-backup", split="validation")
      text_data = dataset["text"][:NUM_CALIBRATION_DATA]

      tokenized_outputs = tokenizer(
      text_data, return_tensors="pt", padding=True, truncation=True, max_length=MAX_SEQ_LEN
      )
      calib_dataloader = DataLoader(
      tokenized_outputs['input_ids'], batch_size=BATCH_SIZE, drop_last=True
      )

#. Define the quantization configuration. See the comments in the following code snippet for descriptions of each configuration option.

   .. code-block:: python

      from quark.torch.quantization import (Config, QuantizationConfig,
                                           FP8E4M3PerTensorSpec)

      # Define fp8/per-tensor/static spec.
      FP8_PER_TENSOR_SPEC = FP8E4M3PerTensorSpec(observer_method="min_max",
          is_dynamic=False).to_quantization_spec()

      # Define global quantization config, input tensors and weight apply FP8_PER_TENSOR_SPEC.
      global_quant_config = QuantizationConfig(input_tensors=FP8_PER_TENSOR_SPEC,
          weight=FP8_PER_TENSOR_SPEC)

      # Define quantization config for kv-cache layers, output tensors apply FP8_PER_TENSOR_SPEC.
      KV_CACHE_SPEC = FP8_PER_TENSOR_SPEC
      kv_cache_layer_names_for_llama = ["*k_proj", "*v_proj"]
      kv_cache_quant_config = {name :
          QuantizationConfig(input_tensors=global_quant_config.input_tensors,
                             weight=global_quant_config.weight,
                             output_tensors=KV_CACHE_SPEC)
          for name in kv_cache_layer_names_for_llama}
      layer_quant_config = kv_cache_quant_config.copy()

      EXCLUDE_LAYERS = ["lm_head"]
      quant_config = Config(
          global_quant_config=global_quant_config,
          layer_quant_config=layer_quant_config,
          kv_cache_quant_config=kv_cache_quant_config,
          exclude=EXCLUDE_LAYERS)

#. Quantize the model and export

   .. code-block:: python

      import torch
      from quark.torch import ModelQuantizer, ModelExporter
      from quark.torch.export import ExporterConfig, JsonExporterConfig

      # Apply quantization.
      quantizer = ModelQuantizer(quant_config)
      quant_model = quantizer.quantize_model(model, calib_dataloader)

      # Freeze quantized model to export.
      freezed_model = quantizer.freeze(model)

      # Define export config.
      LLAMA_KV_CACHE_GROUP = ["*k_proj", "*v_proj"]
      export_config = ExporterConfig(json_export_config=JsonExporterConfig())
      export_config.json_export_config.kv_cache_group = LLAMA_KV_CACHE_GROUP

      EXPORT_DIR = MODEL_ID.split("/")[1] + "-w-fp8-a-fp8-kvcache-fp8-pertensor"
      exporter = ModelExporter(config=export_config, export_dir=EXPORT_DIR)
      with torch.no_grad():
          exporter.export_safetensors_model(freezed_model,
              quant_config=quant_config, tokenizer=tokenizer)

Evaluating the quantized model with vLLM
----------------------------------------

The exported Quark-quantized model can be loaded directly by vLLM for inference. You need to specify the model path and inform vLLM about the quantization method (``quantization='quark'``) and the KV cache data type (``kv_cache_dtype='fp8'``).
Use the ``LLM`` interface to load the model:

.. code-block:: python

   from vllm import LLM, SamplingParamsinterface

   # Sample prompts.
   prompts = [
       "Hello, my name is",
       "The president of the United States is",
       "The capital of France is",
       "The future of AI is",
   ]
   # Create a sampling params object.
   sampling_params = SamplingParams(temperature=0.8, top_p=0.95)

   # Create an LLM.
   llm = LLM(model="Llama-2-70b-chat-hf-w-fp8-a-fp8-kvcache-fp8-pertensor",
             kv_cache_dtype='fp8',quantization='quark')
   # Generate texts from the prompts. The output is a list of RequestOutput objects
   # that contain the prompt, generated text, and other information.
   outputs = llm.generate(prompts, sampling_params)
   # Print the outputs.
   print("\nGenerated Outputs:\n" + "-" * 60)
   for output in outputs:
       prompt = output.prompt
       generated_text = output.outputs[0].text
       print(f"Prompt:    {prompt!r}")
       print(f"Output:    {generated_text!r}")
       print("-" * 60)

You can also evaluate the quantized model's accuracy on standard benchmarks using the `lm-evaluation-harness <https://github.com/EleutherAI/lm-evaluation-harness>`_. Pass the necessary vLLM arguments to ``lm_eval`` via ``--model_args``.

.. code-block:: shell

   lm_eval --model vllm \
     --model_args pretrained=Llama-2-70b-chat-hf-w-fp8-a-fp8-kvcache-fp8-pertensor,kv_cache_dtype='fp8',quantization='quark' \
     --tasks gsm8k

This provides a standardized way to measure the performance impact of quantization.
.. _fine-tune-llms-gptq:

GPTQ
====

GPTQ is a post-training quantization technique where each row of the weight matrix is quantized independently to find a
version of the weights that minimizes error. These weights are quantized to ``int4`` but are restored to ``fp16`` on the
fly during inference. This can save your memory usage by a factor of four. A speedup in inference is expected because
inference of GPTQ models uses a lower bit width, which takes less time to communicate.

Before setting up the GPTQ configuration in Transformers, ensure the `AutoGPTQ <https://github.com/AutoGPTQ/AutoGPTQ>`_ library
is installed.

Installing AutoGPTQ
-------------------

The AutoGPTQ library implements the GPTQ algorithm.

#. Use the following command to install the latest stable release of AutoGPTQ from pip.

   .. code-block:: shell

      # This will install pre-built wheel for a specific ROCm version.

      pip install auto-gptq --no-build-isolation --extra-index-url https://huggingface.github.io/autogptq-index/whl/rocm573/

   Or, install AutoGPTQ from source for the appropriate ROCm version (for example, ROCm 6.1).

   .. code-block:: shell

      # Clone the source code.
      git clone https://github.com/AutoGPTQ/AutoGPTQ.git
      cd AutoGPTQ

      # Speed up the compilation by specifying PYTORCH_ROCM_ARCH to target device.
      PYTORCH_ROCM_ARCH=gfx942 ROCM_VERSION=6.1 pip install .

      # Show the package after the installation 

#. Run ``pip show auto-gptq`` to print information for the installed ``auto-gptq`` package. Its output should look like
   this:

   .. code-block:: shell

      Name: auto-gptq
      Version: 0.8.0.dev0+rocm6.1
      ...

Using GPTQ with AutoGPTQ
------------------------

#. Run the following code snippet.

   .. code-block:: python

         from transformers import AutoTokenizer, TextGenerationPipeline
         from auto_gptq import AutoGPTQForCausalLM, BaseQuantizeConfig
         base_model_name = "NousResearch/Llama-2-7b-hf"
         quantized_model_name = "llama-2-7b-hf-gptq"
         tokenizer = AutoTokenizer.from_pretrained(base_model_name, use_fast=True)
         examples = [
             tokenizer(
                 "auto-gptq is an easy-to-use model quantization library with user-friendly apis, based on GPTQ algorithm."
             )
         ]
         print(examples)

   The resulting examples should be a list of dictionaries whose keys are ``input_ids`` and ``attention_mask``.

#. Set up the quantization configuration using the following snippet.

   .. code-block:: python

      quantize_config = BaseQuantizeConfig(
          bits=4,  		# quantize model to 4-bit
          group_size=128,  	# it is recommended to set the value to 128
          desc_act=False,  
      )

#. Load the non-quantized model using the AutoGPTQ class and run the quantization.

   .. code-block:: python

      # Import auto_gptq class.
      from auto_gptq import AutoGPTQForCausalLM

      # Load non-quantized model.
      base_model = AutoGPTQForCausalLM.from_pretrained(base_model_name, quantize_config, device_map = "auto")
      base_model.quantize(examples)

      # Save quantized model.
      base_model.save_quantized(quantized_model_name)

Using GPTQ with Hugging Face Transformers
------------------------------------------

#. To perform a GPTQ quantization using Hugging Face Transformers, you need to create a ``GPTQConfig`` instance and set the
   number of bits to quantize to, and a dataset to calibrate the weights.

   .. code-block:: python

      from transformers import AutoModelForCausalLM, AutoTokenizer, GPTQConfig

      base_model_name = " NousResearch/Llama-2-7b-hf"
      tokenizer = AutoTokenizer.from_pretrained(base_model_name)
      gptq_config = GPTQConfig(bits=4, dataset="c4", tokenizer=tokenizer)

#. Load a model to quantize using ``AutoModelForCausalLM`` and pass the
   ``gptq_config`` to its ``from_pretained`` method. Set ``device_map=”auto”`` to
   automatically offload the model to available GPU resources.

   .. code-block:: python

      quantized_model = AutoModelForCausalLM.from_pretrained(
                              base_model_name, 
                              device_map="auto", 
                              quantization_config=gptq_config)

#. Once the model is quantized, you can push the model and tokenizer to Hugging Face Hub for easy share and access.

   .. code-block:: python

      quantized_model.push_to_hub("llama-2-7b-hf-gptq")
      tokenizer.push_to_hub("llama-2-7b-hf-gptq")

   Or, you can save the model locally using the following snippet.

   .. code-block:: python

      quantized_model.save_pretrained("llama-2-7b-gptq")
      tokenizer.save_pretrained("llama-2-7b-gptq")

ExLlama-v2 support
------------------

ExLlama is a Python/C++/CUDA implementation of the Llama model that is
designed for faster inference with 4-bit GPTQ weights. The ExLlama
kernel is activated by default when users create a ``GPTQConfig`` object. To
boost inference speed even further on Instinct GPUs, use the ExLlama-v2
kernels by configuring the ``exllama_config`` parameter as the following.

.. code-block:: python

   from transformers import AutoModelForCausalLM, GPTQConfig
   #pretrained_model_dir = "meta-llama/Llama-2-7b"
   base_model_name = "NousResearch/Llama-2-7b-hf"
   gptq_config = GPTQConfig(bits=4, dataset="c4", exllama_config={"version":2})
   quantized_model = AutoModelForCausalLM.from_pretrained(
                           base_model_name,
                           device_map="auto",
                           quantization_config=gptq_config)

bitsandbytes
============

The `ROCm-aware bitsandbytes <https://github.com/ROCm/bitsandbytes>`_ library is
a lightweight Python wrapper around CUDA custom functions, in particular 8-bit optimizer, matrix multiplication, and
8-bit and 4-bit quantization functions. The library includes quantization primitives for 8-bit and 4-bit operations
through ``bitsandbytes.nn.Linear8bitLt`` and ``bitsandbytes.nn.Linear4bit`` and 8-bit optimizers through the
``bitsandbytes.optim`` module. These modules are supported on AMD Instinct GPUs.

Installing bitsandbytes
-----------------------

#. To install bitsandbytes for ROCm 6.0 (and later), use the following commands.

   .. code-block:: shell

      # Clone the github repo
      git clone --recurse https://github.com/ROCm/bitsandbytes.git
      cd bitsandbytes
      git checkout rocm_enabled_multi_backend

      # Install dependencies 
      pip install -r requirements-dev.txt

      # Use -DBNB_ROCM_ARCH to specify target GPU arch
      cmake -DBNB_ROCM_ARCH="gfx942" -DCOMPUTE_BACKEND=hip -S .

      # Compile the project
      make

      # Install 
      python setup.py install

#. Run ``pip show bitsandbytes`` to show the information about the installed bitsandbytes package. Its output should
   look like the following.

   .. code-block:: shell

      Name: bitsandbytes
      Version: 0.44.0.dev0
      ...

Using bitsandbytes primitives
-----------------------------

To get started with bitsandbytes primitives, use the following code as reference.

.. code-block:: python

   import bitsandbytes as bnb

   # Use Int8 Matrix Multiplication
   bnb.matmul(..., threshold=6.0)

   # Use bitsandbytes 8-bit Optimizers
   adam = bnb.optim.Adam8bit(model.parameters(), lr=0.001, betas=(0.9, 0.995))

Using bitsandbytes with Hugging Face Transformers
-------------------------------------------------

To load a Transformers model in 4-bit, set ``load_in_4bit=true`` in ``BitsAndBytesConfig``.

.. code-block:: python

   from transformers import AutoModelForCausalLM, BitsAndBytesConfig

   base_model_name = "NousResearch/Llama-2-7b-hf"
   quantization_config = BitsAndBytesConfig(load_in_4bit=True)
   bnb_model_4bit = AutoModelForCausalLM.from_pretrained(
           base_model_name, 
           device_map="auto", 
           quantization_config=quantization_config)

   # Check the memory footprint with get_memory_footprint method
   print(bnb_model_4bit.get_memory_footprint())

To load a model in 8-bit for inference, use the ``load_in_8bit`` option.

.. code-block:: python

   from transformers import AutoModelForCausalLM, AutoTokenizer, BitsAndBytesConfig

   base_model_name = "NousResearch/Llama-2-7b-hf"

   tokenizer = AutoTokenizer.from_pretrained(base_model_name)
   quantization_config = BitsAndBytesConfig(load_in_8bit=True)
   tokenizer = AutoTokenizer.from_pretrained(base_model_name)
   bnb_model_8bit = AutoModelForCausalLM.from_pretrained(
           base_model_name, 
           device_map="auto", 
           quantization_config=quantization_config)

   prompt = "What is a large language model?"
   inputs = tokenizer(prompt, return_tensors="pt").to("cuda")
   generated_ids = model.generate(**inputs)
   outputs = tokenizer.batch_decode(generated_ids, skip_special_tokens=True)