Quantizing a Large Language Model with Quark
============================================

In this tutorial, we will be quantizing a Large Language Model (LLM)
using AMD Quark. We are following on from the *Quantizing a Diffusion
Model using Quark* tutorial. If you are not familiar with quantization,
we recommended having a look at the `Quickstart
Tutorial <https://quark.docs.amd.com/latest/tutorials/torch/quickstart_tutorial/quickstart_tutorial.html>`__
first.

What You Will Learn
-------------------

- Large Language Model fundamentals
- AMD Command Line Interface (CLI) for Quantization
- Advanced quantization algorithms
- Comparing the model’s accuracy before and after quantization using
  benchmarks
- Exporting using Hugging Face format

Installation and Setup
----------------------

Please refer to `Recommended First Time User
Installation <https://quark.docs.amd.com/latest/install.html>`__ for
necessary packages imports, and `AMD Quark Tutorial: PyTorch
Quickstart <https://quark.docs.amd.com/latest/tutorials/torch/quickstart_tutorial/quickstart_tutorial.html>`__
for setting up Linux for Windows machines usign WSL (Windows Subsystem
for Linux). As we will be using the CLI for this tutorial, WSL is needed
to run our scripts using Linux to download, quantize and evaluate our
model.

If you have not already completed the *diffusion model* tutorial, we
must install the necessary additional packages required for this
tutorial. You can run the commands:

.. code:: bash

   pip install accelerate notebook safetensors transformers huggingface_hub[cli]

If you are using GPUs compatible with ROCm (AMD GPUs), you can install
the PyTorch version below to accelerate runtime. You should check
`PyTorch’s installation
page <https://pytorch.org/get-started/locally/>`__ for instructions on
installing an up-to-date version for your system. For example, we used
ROCm 6.2.4 in this tutorial, which we installed as follows:

.. code:: bash

   pip install torch torchvision torchaudio --index-url https://download.pytorch.org/whl/rocm6.2.4

If you are using GPUs compatible with CUDA (NVIDIA GPUs), you can
install the below version instead. This tutorial uses CUDA 12.6, but
feel free to swap it out for a different version.

.. code:: bash

   pip install torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu126

You can also install the requirements necessary to run Quark with the
below:

.. code:: bash

   pip install amd-quark

By default, Hugging Face uses paths stored in environment variables
``HUGGINGFACE_HUB_CACHE``, and ``HF_DATASETS_CACHE`` as the location to
cache downloaded models and datasets, respectively. You can set these
environment variables to specify your own paths. By default they will be
under ``~/.cache/huggingface/hub/`` and
``~/.cache/huggingface/datasets/``.

We will be using the example scripts available in the Quark github
repository to run our CLI scripts.

Large Language Model Fundamentals
---------------------------------

Chunking & Tokenization
~~~~~~~~~~~~~~~~~~~~~~~

Tokenization converts the user’s prompt into a numerical representation
called tokens. In production-use LLMs like ChatGPT, tokens are generally
subsections of a word. For example, the word ``Ireland`` may be split
into ``Ire`` and ``land``. However, sometimes tokenization is performed
at a character or word level. Special characters, such as ``<UNK>`` for
unknown words, or ``<PAD>`` for padding, ``<EOS>`` for end of sentence,
are also included.

Text Encoding
~~~~~~~~~~~~~

The tokens are mapped to their corresponding integers, to allow the
computer to read them. This is called *text encoding*.

In each layer, the token is contextualized within a context window; a
fixed-length of surrounding tokens (think: a word in a sentence).
Higher-importance tokens within the context window are prioritized using
an attention mechanism; more on this later. In a LLM, the model uses the
context window to generate the next most likely token in a sequence.

|image1|

The tokens are usually processed in parallel, to speed up compute time.
This is why we check if we can use a GPU with
``torch.cuda.is_available()``, as GPUs are very efficient at processing
data in parallel. However, this means we lose the position of the words
in our sentences/tokens in our context window. To solve this, we add a
*positional embedding*. You can think about it like a dictionary of
tokens with a corresponding index associated with it:

|image2|

To process a large text into smaller and more manageable pieces for the
model to interpret, the text is split into sections called *chunks* to
allow the LLM to process it within its context window.

Latent Space
~~~~~~~~~~~~

While the machine can now read our text encodings, there is no way for
the machine to relate other tokens to each other. We can solve this
issue by mapping all the encodings into a *co-ordinate space* (think:
each token will now have a physical co-ordinate, or location, on a map
or grid), with the distance between encodings being their closeness in
relation to each other. We call this mapping a *latent space*. You can
think of it as below:

|image3|

You can clearly see the different categories as below:

|image4|

In a computer, however, instead of a two-dimensional space, it is
*n*-dimensional. The emojis, depicted above, can represent the machine’s
understanding of the word as a floating-point number, which corresponds
to its coordinate in latent space. For example, the model might think in
the following way:

:math:`king - man + woman ~= queen`

which could be something similar as below:

:math:`0.51-0.22 + 0.24 ~= 0.528`

As seen in the diagrams, similar concepts cluster together. Directions
in the space can correspond to features like tense, plurality, or
sentiment.

We can put together the tokenization -> text encoding -> latent space as
follows:

.. figure::
   ../../../../_static/llm_tutorial_images/prompt_processing.png
   :alt: prompt_processing

   prompt_processing

It’s important to note that LLMs are unambiguous; i.e. each word is
context-dependent. With human language, words may have dual meanings,
such as orange meaning a fruit and a colour. The model uses the context
window to figure out which meaning the word has, during content
generation/inference.

Transformers & Attention
~~~~~~~~~~~~~~~~~~~~~~~~

Transformers are most famous for their use in LLMs, however they are
also used in computer vision, audio processing, and other tasks. We need
to make sure that more important words are prioritized in our context
for our next token generation. This is where transformers come into
play; they are able to distinguish between important vs. not as
important parts of information during inference (prompting) and
training. As transformers can also be used in image segmentation tasks,
we can think about the attention mechanism visually as below:

|image5|

The important part of the picture, the two rabbits, are extracted. The
background is not considered as much when classifying, as we are looking
for the focus of the image; the two rabbits. This is very similar when
we consider prompts. For example, if we have the prompt:

``The capital of Ireland is``

the model puts its focus on ``capital`` and ``Ireland``, and does not
consider the other words as much, like ``the``, ``of``, and ``is``, as
their addition does not change the meaning of the sentance as much. If
the user inputted ``capital Ireland``, the model would still associate
it with ``Dublin`` despite the incomplete sentence.

Testing with *Microsoft Copilot*, we can see this is the case, with
slight variations in its response:

|image6|

compared to

|image7|

The reasoning can be visualized as follows:

|image8|

Within the transformer architecture, the self-attention mechanism
computes the attention scores so the transformer model knows which words
to assign more priority to. It uses ``Query``, ``Key`` and ``Value``
``(Q, K, V)`` values to assign these priorities.

We can think about the ``Query``, ``Key`` and ``Value`` intuitively by
considering a search query, as below:

|image9|

The ``Query`` is the search. The ``Key`` is the indexes or titles of the
links returned (like “Quantization (signal processing)”). The ``Value``
is the actual information within the ``Key``; for example, the Wikipedia
page itself.

We can calculate the attention. The output of the transformer can be
calculated through the dot product of the ``Query`` and ``Key`` tokens.
We then use a *softmax* to get the attention weights. The ``Value``
vectors are weighted by this result.

Putting it all together, we can now make our transformer architecture as
below:

|image10|

LLMs use *Multi-Headed* attention; this allows the model to have
different relationships between words. This is like our example from
earlier with the orange representing a colour and a fruit. Each head has
it’s own sub-space these results are joined together and projected back
into the latent space.

Model Architecture
~~~~~~~~~~~~~~~~~~

Once the attention has been computed, the output is fed through a neural
network. This is composed of multiple transformer blocks, with a
self-attention mechanism and a feed-forward neural network. This
structure allows the model to get the different hierarchical
representations of the text.

The final layer is a softmax layer that converts our output into
probabilities, to select the next most likely token.

The full LLM architecture can be described as below:

|image11|

To break it down, the LLM processes and outputs text as follows:

1.  User inputs a prompt
2.  Prompt is chunked & tokenized
3.  Tokens are embedded into latent space
4.  Positional encodings are added
5.  Input is fed through a series of transformer blocks for processing
6.  Output is fed through a linear layer for transforming into correct
    size
7.  Output is fed through softmax to get output in the range
    :math:`[0,1]`; i.e. their probabilities
8.  Token probabilities are generated from softmax to find next most
    probable word
9.  Next token is repeatedly generated from next most probable outcome
10. This process is repeated until until max token limit is reached.

.. |image1| image:: ../../../../_static/llm_tutorial_images/generation.png
.. |image2| image:: ../../../../_static/llm_tutorial_images/positional_encoding.png
.. |image3| image:: ../../../../_static/llm_tutorial_images/associations.png
.. |image4| image:: ../../../../_static/llm_tutorial_images/latent_space_clustering.png
.. |image5| image:: ../../../../_static/llm_tutorial_images/attention_mechanism.png
.. |image6| image:: ../../../../_static/llm_tutorial_images/prompt_long.png
.. |image7| image:: ../../../../_static/llm_tutorial_images/prompt_short.png
.. |image8| image:: ../../../../_static/llm_tutorial_images/prompt_attention.png
.. |image9| image:: ../../../../_static/llm_tutorial_images/query_key_value.png
.. |image10| image:: ../../../../_static/llm_tutorial_images/transformer.png
.. |image11| image:: ../../../../_static/llm_tutorial_images/llm_architecture.png

CLI Scripts
-----------

Now that we have covered the theory of the architecture of LLMs, we can
get started with our code implementation. We will be using Quark’s
Command Line Interface (CLI). This means we will be running our scripts
using the terminal, rather than writing the python scripts directly.

The following quantization portion of this tutorial is intended to run
with a GPU, since it can process tensor operations much faster than a
CPU due to its parallel architecture. You can test if you have the
correct access by running the script below. If the output returns
``True``, you have access to a compatible GPU. Otherwise, you will be
running on CPU.

.. code:: ipython3

    import torch
    
    torch.cuda.is_available()

Downloading the Model
~~~~~~~~~~~~~~~~~~~~~

We will be using Mistral’s 7B instruct model during this tutorial, but
feel free to switch in for another model if you would like! It’s
important to note that only a select few models are supported by the
CLI; you can view a list of them
`here <https://quark.docs.amd.com/latest/pytorch/example_quark_torch_llm_ptq.html>`__.

If you have not already done so, make sure to create a Hugging Face
account so we can download the models for use. Like in the previous
tutorial on diffusion models, we need to request access to the
repository so we can download it. You can navigate to the following
link:
`mistralai/Mistral-7B-v0.1 <https://huggingface.co/mistralai/Mistral-7B-v0.1>`__.
Click the button to access the repo:

.. figure:: ../../../../_static/llm_tutorial_images/access_repo.png
   :alt: access_repo

   access_repo

Once you have access, you can try running the below command to download
a Llama model from Hugging Face and evaluate it’s performance prior to
quantization. You can switch out a different model from the supported
list by copying the repo name:

.. figure:: ../../../../_static/llm_tutorial_images/copy_repo_name.png
   :alt: copy_repo_name

   copy_repo_name

and switching it out from ``mistralai/Mistral-7B-v0.1``.

Please note that the ``mistral-7B`` model requires 14.48 GB of storage.
Consider switching to a smaller model like
`llama-1b <https://huggingface.co/meta-llama/Llama-3.2-1B>`__, which
requires 2.5 GB of storage if you do not have enough room on your
device. A general rule of thumb is the larger the number of parameters,
the more accurate the model is, the more compute it will take to run,
and the larger its file size is.

Login to the Hugging Face API locally by running the below in your
terminal and inputting your token: ``huggingface-cli login``

Now, we can download our model. You can see the commands within the CLI
to specify what task we are doing; ``model_dir`` refers to the path from
our copied Hugging Face dir, and we set the ``skip_quantization`` flag
as we want to just download our model right now.

.. code:: ipython3

    !hf download mistralai/Mistral-7B-v0.1

Model Evaluation: Pre-Quantization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As we will be quantizing our model, i.e. reducing the precision of our
model’s weights to improve performance speed, we need a way to measure
the degradation in quality. In the previous tutorial on diffusion model
quantization, we were able to compare the quality degradation through
our generated images, however with text outputs, it isn’t as obvious
where the degradation in quality is. Therefore, we need to test or
benchmark our model before and after quantization, rather than just
reviewing the outputs.

We will be using a test called *Measuring Massive Multitask Language
Understanding*. This test measures an LLM’s multitask accuracy in 57
tasks including elementary mathematics, law, US history, computer
science, and more. We will be testing just a few tasks from MMLU as
otherwise, it will take a long time to run. The tasks are divided into
four categories; humanities, other, social sciences, and STEM. We will
be taking one from each category; professional law from humanities,
management from others, sociology from social sciences, and machine
learning from STEM.

Let’s set our model directory path to call in our bash script. The model
directory should be downloaded into the ``.cache`` folder as a default,
as below.

.. figure:: ../../../../_static/llm_tutorial_images/model_dir.png
   :alt: model_dir

   model_dir

If we were specifying this as our model checkpoint, we could set it
using the command below:

.. code:: bash

   MODEL_PATH=/.cache/huggingface/transformers/models--mistralai--Mistral-7B-v0.1/snapshots/27d67f1b5f57dc0953326b2601d68371d40ea8da

Note that the snapshot changes for each user. The large number,
``27d67f1b5f57dc0953326b2601d68371d40ea8da`` is used to differentiate
between multiple downloaded models of the same type, so we can download
the same ``mistralai`` model multiple times for different purposes.

Now, we can call our bash script as below:

.. code:: sh

    %%sh
    SNAPSHOT=$(ls "$HUGGINGFACE_HUB_CACHE/models--mistralai--Mistral-7B-v0.1/snapshots" | head -n 1)
    MODEL_PATH="$HUGGINGFACE_HUB_CACHE/models--mistralai--Mistral-7B-v0.1/snapshots/$SNAPSHOT"


.. code:: ipython3

    # Set the path to your snapshot here, as in described above:
    # MODEL_PATH=.cache/huggingface/transformers/models--mistralai--Mistral-7B-v0.1/snapshots/27d67f1b5f57dc0953326b2601d68371d40ea8da/
    
    !python examples/torch/language_modeling/llm_eval/llm_eval.py --model_args pretrained=$MODEL_PATH --model hf --tasks mmlu_professional_law,mmlu_management,mmlu_sociology,mmlu_machine_learning --batch_size 1 --device cuda

The output should be similar to the below:

.. figure:: ../../../../_static/llm_tutorial_images/prequant_stats.png
   :alt: prequant_stats

   prequant_stats

Quantization
~~~~~~~~~~~~

Now that we have evaluated our model performance, let’s quantize and
export our model. We will be quantizing our model using ``int4``
quantization. Hugging Face models are typically stored in ``FP32``; this
means there is an x8 decrease in weight size from our original model.

However, with such an aggressive quantization method, the accuracy of
our model will be greatly impacted, especially considering it is already
a significantly smaller model than used in industry at 7 billion
parameters compared to GPT-3, which has 175 billion, or GPT-4, which is
estimated to be around 1.76 trillion parameters. Therefore, we must
think about if there is any ways we could *select* some weights for
quantization while leaving more important ones at full accuracy, to make
sure our quality does not degrade too much.

This is where quantization algorithms come into play. In this tutorial,
we will be using a quantization algorithm called *AWQ: Activation-aware
Weight Quantization*, specifically designed for low-bit precision like
``int4``. In LLMs, not all weights contribute equally to model
performance; even by just protecting 1% of higher-importance weights, we
can greatly reduce the quantization error. This is done by checking the
model activations to see which weights are of importance. Take the
diagram below of a tiny neural network:

.. figure:: ../../../../_static/llm_tutorial_images/neuron.png
   :alt: neuron

   neuron

The output of this simple network in the image can be calculated by
taking the dot product of our weights with our inputs, then adding our
bias and putting it into the activation function. In our LLM
transformer, these layers are stacked on top of one another, and when we
input a prompt, the embeddings are filtered through the model,
activating different neurons. With AWQ, we see which of these
activations are selected frequently in high-importance, and only
quantize the ones which are not as critical to performance.

To select the activated neurons, we have to have a calibration set to
let our model measure the activations. We will be using the
``pileval_for_awq_benchmark`` dataset as specified in our CLI command.
We will be exporting our model in ``hf_format``, so we can test the
quantization benchmark again later.

Let’s run the below script to quantize our model weights with
``int4 AWQ`` quantization and save it to a new folder called
``quantized_llm``.

.. code:: ipython3

    !python3 quantize_quark.py --model_dir $MODEL_PATH --output_dir output_dir --quant_scheme int4_wo_128 --num_calib_data 128 --quant_algo awq --dataset pileval_for_awq_benchmark --seq_len 512 --model_export hf_format

.. code:: bash

   python3 quantize_quark.py --model_dir $MODEL_PATH \ 
   --output_dir output_dir \ 
   --quant_scheme int4_wo_128 \ 
   --num_calib_data 128 \ 
   --quant_algo awq \ 
   --dataset pileval_for_awq_benchmark \ 
   --seq_len 512 \ 
   --model_export hf_format

Model Evaluation: Post-Quantization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Now that we have quantized our model, let’s benchmark it again using the
same script from earlier.

.. code:: bash

   !python llm_eval.py \ 
       --model_args pretrained="llm_quant"\ 
       --model hf \ 
       --tasks mmlu_professional_law,mmlu_management,mmlu_sociology,mmlu_machine_learning \ 
       --batch_size 1 \ 
       --device cuda

Further Reading
---------------

Tutorials/Articles
~~~~~~~~~~~~~~~~~~

- `On the Biology of a Large Language
  Model <https://transformer-circuits.pub/2025/attribution-graphs/biology.html>`__

  - Explains the internals of how LLMs “think” beyond just a black box

- `Hugging Face LLM
  Course <https://huggingface.co/learn/llm-course/chapter1/3?fw=pt>`__

  - More in-depth description on the background of LLM models

- `GPT from scratch <https://www.youtube.com/watch?v=kCc8FmEb1nY>`__

  - A video on creating a LLM from scratch in PyTorch, by a founding
    engineer of ChatGPT, Andrej Karpathy

- `AMD GPU ONNX
  runtime <https://huggingface.co/docs/optimum/onnxruntime/usage_guides/amdgpu>`__

  - Detailing how to use ONNX runtime on AMD GPUs for inference using
    ONNX

Papers
~~~~~~

- `Attention Is All you Need <https://arxiv.org/pdf/1706.03762>`__

  - Original Transformer model paper; based on language translation
    tasks

- `Improving Language Understanding by Generative
  Pre-Training <https://cdn.openai.com/research-covers/language-unsupervised/language_understanding_paper.pdf>`__

  - Introduces the original ChatGPT; the first pretrained Transformer
    model

- `A Latent Space Theory for Emergent Abilities in Large Language
  Models <https://arxiv.org/pdf/2304.09960>`__

  - Examining latent space clustering for words in LLMs

- `Measuring Massive Multitask Language
  Understanding <https://arxiv.org/abs/2009.03300>`__

  - Introduction to the method used to evaluate our LLM performance;
    MMLU

- `AWQ: Activation-aware Weight Quantization for LLM Compression and
  Acceleration <https://arxiv.org/abs/2306.00978>`__

  - Weight selection for quantization accuracy
