手撕大模型，KVCache 原理及代码解析

Core Insights - The article discusses the importance of KV Cache in enhancing the efficiency of large language models (LLMs) during autoregressive inference, particularly in the context of the Transformer architecture [1][20]. Group 1: Need for KV Cache - KV Cache is essential for storing intermediate computation results, which significantly improves the model's operational efficiency during text generation tasks [1][20]. - In standard Transformer decoding, each new token generation requires attention calculations that involve all previous tokens, leading to high computational complexity [2][6]. Group 2: Working Principle of KV Cache - The core idea of KV Cache is to cache the historical Key (K) and Value (V) matrices, thus avoiding redundant calculations and reducing time complexity from O(n²) to O(n) [4][7]. - The process involves calculating the new Query (Q) matrix and performing attention calculations with the cached K and V matrices, allowing for efficient token generation [4][10]. Group 3: Technical Details of KV Cache - KV Cache typically maintains independent caches for each attention head, with the cache structure dynamically growing until it reaches the model's maximum sequence length [11]. - While KV Cache improves speed, it requires additional memory, with models like GPT-3 consuming approximately 20KB of memory per token, leading to significant memory usage during batch processing [12]. Group 4: Optimization Strategies for KV Cache - Strategies such as Paged KV Cache, dynamic cache management, quantization, and selective caching are employed to enhance the efficiency of KV Cache while managing memory usage [22][18]. Group 5: Code Implementation - The article provides a code example demonstrating the implementation of KV Cache in self-attention mechanisms using PyTorch, highlighting the modifications needed to incorporate caching [14][17]. Group 6: Conclusion - Understanding the workings of KV Cache is crucial for optimizing inference performance in large models and addressing challenges in practical deployment [20].