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Applying 2:4 Sparsity with Optional FP8 Quantization

This script demonstrates how to apply 2:4 structured sparsity with and without FP8 quantization to the Meta-Llama-3-8B-Instruct model using the llm-compressor library. The compressed model is optimized for memory efficiency and faster inference on supported GPUs.

Note: FP8 dynamic precision computation is supported on Nvidia GPUs with CUDA Compute Capability 9.0 and above.

Installation

To get started, install the llm-compressor library and its dependencies:

git clone https://github.com/vllm-project/llm-compressor.git
cd llm-compressor
pip install -e .

Quickstart

Run the script with the following commands:

  • Without FP8 Quantization:
python3 llama3_8b_2of4.py
  • With FP8 Quantization:
python3 llama3_8b_2of4.py --fp8

The script compresses the Meta-Llama-3-8B-Instruct model using:

  • 2:4 Structured Sparsity: Applies structured pruning to reduce weights by 50%.
  • FP8 Quantization (Optional): Enables dynamic quantization for further memory savings.

Configuration

  • Model: meta-llama/Meta-Llama-3-8B-Instruct
  • Dataset: HuggingFaceH4/ultrachat_200k (train split)
  • Calibration Samples: 512
  • Maximum Sequence Length: 2048

Steps to Run

  1. Select Model, Dataset, and Recipe

The model and dataset are predefined in the script. The recipe dynamically adjusts the recipe based on whether FP8 quantization is enabled (--fp8 flag).

Example Recipe:

recipe = [
    SparseGPTModifier(
        sparsity=0.5,
        mask_structure="2:4",
        targets=[r"re:model.layers.\d*$"],
    )
]

if fp8_enabled:
    recipe.append(
        QuantizationModifier(
            targets=["Linear"],
            ignore=["lm_head"],
            scheme="FP8_DYNAMIC",
        ),
    )
  1. Apply Compression The script applies compression using the oneshot function:
oneshot(
    model=model,
    dataset=ds,
    recipe=recipe,
    max_seq_length=2048,
    num_calibration_samples=512,
)

Saving the Compressed Model

The compressed model and tokenizer are saved to the output directory:

model.save_pretrained(save_dir, save_compressed=True)
tokenizer.save_pretrained(save_dir)

Output Directories:

  • Without FP8: Meta-Llama-3-8B-Instruct-2of4-sparse
  • With FP8: Meta-Llama-3-8B-Instruct-2of4-W8A8-FP8-Dynamic-Per-Token

Saving Without Sparse Compression

To save the model on disk without sparse compression:

model.save_pretrained(save_dir, save_compressed=True, disable_sparse_compression=True)
tokenizer.save_pretrained(save_dir)

Note: Saving a model with both the save_compressed and disable_sparse_compression options will compress the model using the quantization compressor; however, instead of using the more disk-efficient sparsity compressor(s), the dense sparsity compressor will be used. The dense sparsity compressor saves model params as is, and does not leverage sparsity for disk-efficient storage. These options only affect how the model(s) are saved on disk and do not impact the actual pruning or quantization processes.

Validation

After compression, the script validates the model by generating a sample output:

========== SAMPLE GENERATION ============
Hello my name is ...
=========================================

Notes:

  • Ensure your GPU has sufficient memory (at least ~25GB) to run compression script.
  • Use the --fp8 flag to enable FP8 quantization.

Modify the MODEL_ID and DATASET_ID variables to use other models or datasets.

Running in vLLM

Install vLLM using pip install vllm

# run_model.py

import argparse
from vllm import LLM, SamplingParams

def run_inference(model_path, tensor_parallel_size, prompt="Hello my name is:"):
    """
    Loads a model and performs inference using LLM.
    """
    # Define sampling parameters
    sampling_params = SamplingParams(
        temperature=0.8,
        top_p=0.95,
    )
    # Load the model
    model = LLM(
        model=model_path, 
        enforce_eager=True,
        dtype="auto",
        tensor_parallel_size=tensor_parallel_size,
    )

    # Generate inference
    outputs = model.generate(prompt, sampling_params=sampling_params)
    return outputs[0].outputs[0].text

def main():
    """ Main function to handle CLI and process the model. """
    # Argument parsing
    parser = argparse.ArgumentParser(description="Run inference on a single model and print results.")
    parser.add_argument(
        "model_path",
        type=str,
        help="Path to the model to perform inference."
    )
    parser.add_argument(
        "--tensor_parallel_size",
        type=int,
        default=1,
        help="Tensor parallel size for the model. Default is 1."
    )

    args = parser.parse_args()
    model_path = args.model_path
    tensor_parallel_size = args.tensor_parallel_size

    prompt = "Hello my name is:"

    # Load model and perform inference
    inference_result = run_inference(model_path, tensor_parallel_size)
    print("="* 20)
    print("Model:", model_path)
    print(prompt, inference_result)

if __name__ == "__main__":
    main()

Command to run model:

python3 run_model.py <MODEL_PATH>

Example:

python3 run_model.py Meta-Llama-3-8B-Instruct2of4-W8A8-FP8-Dynamic-Per-Token