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Blockwise Parameter-Efficient Sparsity Allocation (BESA): An Efficient Technique for Pruning Large Language Models


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A novel pruning technique called Blockwise Parameter-Efficient Sparsity Allocation (BESA) that optimizes pruning rates across different layers of large language models to minimize performance degradation.
Kivonat

This paper introduces a novel pruning technique called Blockwise Parameter-Efficient Sparsity Allocation (BESA) for compressing large language models (LLMs). The key insights are:

  1. BESA operates under a blockwise pruning framework, which minimizes the block-wise reconstruction error instead of the typical layer-wise pruning error. This helps mitigate the accumulation of pruning error across layers.

  2. BESA employs a parameter-efficient sparsity learning algorithm to optimize the pruning rate for each layer. It represents the sparsity as a differentiable combination of learnable pruning probabilities, enabling efficient and effective pruning of LLMs.

  3. BESA can be jointly optimized with weight quantization techniques, further enhancing the compression ratio while maintaining model performance.

Experiments show that BESA achieves state-of-the-art performance in pruning various LLMs, such as LLaMA and LLaMA2, with up to 50% sparsity. It can prune a 70B parameter LLM in just 5 hours on a single A100 GPU, outperforming prior methods like SparseGPT and Wanda in terms of both perplexity and zero-shot capabilities. The paper also demonstrates the practical speedup of the pruned models using a hardware simulator.

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Statisztikák
The paper reports the following key metrics: LLaMA-7B model requires 335GB GPU memory to load in FP16. BESA can prune a 70B parameter LLM in just 5 hours on a single A100 GPU. BESA achieves up to 50% sparsity in LLMs while outperforming prior methods in perplexity and zero-shot capabilities. On the LLaMA-7B model, BESA achieves 1.48x to 1.98x speedup across different layers compared to SparseGPT and Wanda.
Idézetek
"BESA enjoys two advantages for LLM compression. Firstly, the sparsity that was previously considered a non-differentiable hyperparameter can be now equivalently represented by differentiable binary masks. Hence, layer-wise pruning sparsity can be optimized using a simple gradient descent algorithm." "Unlike traditional approaches (Kang & Han, 2020) that learn sparsity for the entire model, BESA optimizes pruning rates sequentially within each transformer block. This enables efficient and differentiable pruning of LLMs ranging from 7B to 180B parameters on a single A100 GPU."

Mélyebb kérdések

How can BESA's blockwise pruning approach be extended to other types of neural network architectures beyond transformers

BESA's blockwise pruning approach can be extended to other types of neural network architectures beyond transformers by adapting the concept of blockwise parameter-efficient sparsity allocation to suit the specific characteristics of different architectures. For example: CNNs (Convolutional Neural Networks): In CNNs, the concept of blocks can be translated to convolutional layers or groups of layers. By applying blockwise reconstruction loss and layer-specific sparsity allocation in CNNs, similar benefits of reduced performance degradation after pruning can be achieved. RNNs (Recurrent Neural Networks): In RNNs, the concept of blocks can be applied to recurrent layers or units. By optimizing pruning rates across different recurrent blocks, the impact of pruning on model performance can be minimized. Graph Neural Networks (GNNs): For GNNs, the blockwise approach can be adapted to graph layers or subgraphs. By implementing blockwise pruning and differentiable sparsity learning in GNNs, efficient compression and optimization of model parameters can be achieved. By customizing the blockwise pruning technique to suit the specific architecture's structure and characteristics, the benefits of BESA in reducing model size and improving efficiency can be extended to a wider range of neural network architectures.

What are the potential limitations of BESA's parameter-efficient sparsity learning, and how could it be further improved

One potential limitation of BESA's parameter-efficient sparsity learning is the scalability of the approach to larger models or more complex architectures. As the model size increases, the number of learnable coefficients for sparsity allocation also grows, leading to increased computational complexity and training time. To address this limitation and further improve the approach, several strategies can be considered: Hierarchical Sparsity Allocation: Introduce a hierarchical sparsity allocation scheme where sparsity is allocated at different levels of granularity, such as at the block level, layer level, and neuron level. This hierarchical approach can reduce the number of learnable parameters and improve scalability. Dynamic Sparsity Learning: Implement dynamic sparsity learning techniques that adaptively adjust sparsity rates during training based on the model's performance and training progress. This dynamic approach can enhance the flexibility and adaptability of sparsity allocation. Regularization Techniques: Incorporate regularization methods to prevent overfitting and improve the generalization of the sparsity learning process. Techniques like L1/L2 regularization can help control the complexity of the sparsity allocation model and enhance its robustness. By addressing these potential limitations and incorporating advanced strategies, BESA's parameter-efficient sparsity learning can be further refined and optimized for more efficient and effective model compression.

Could the insights from BESA be applied to develop efficient techniques for fine-tuning or adapting pruned large language models to specific tasks or domains

The insights from BESA can be applied to develop efficient techniques for fine-tuning or adapting pruned large language models to specific tasks or domains by leveraging the following strategies: Task-Specific Pruning: Utilize BESA's blockwise pruning approach to identify and retain important weights for specific tasks or domains during the pruning process. By preserving task-relevant information, the pruned model can be fine-tuned more effectively for targeted applications. Domain-Specific Sparsity Allocation: Implement BESA's parameter-efficient sparsity learning to allocate sparsity in a task-specific manner, focusing on the most relevant parts of the model for the target domain. This targeted sparsity allocation can enhance the model's performance and adaptability to specific tasks. Transfer Learning with Pruned Models: Use pruned models generated by BESA as a starting point for transfer learning on new tasks or domains. By fine-tuning the pruned model with task-specific data, the model can quickly adapt to new tasks while maintaining efficiency and performance gains from pruning. By integrating these insights into the fine-tuning and adaptation process, BESA's techniques can be leveraged to streamline the deployment of pruned large language models for diverse applications and domains.
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