Large Language Models Manage Long Contexts with Attention and More

Hi All, I wrote a blog post exploring how large language models (LLMs) manage long contexts, covering everything from basic attention math to million-token inference across multiple GPUs. The post is structured into three parts: Part 1 discusses how attention functions, the challenges posed by the KV cache at long contexts, and how Flash Attention addresses this issue by utilizing fast on-chip memory for tiling computations instead of creating large attention matrices. Part 2 examines scenarios where a model exceeds the capacity of a single GPU. It delves into tensor parallelism, the operation of all-reduce collectives over NVLink, and the implementation of ring attention for distributing long sequences across GPUs. Part 3 focuses on position encoding techniques (RoPE, YaRN) and how newer architectures either compress or replace the KV cache. It highlights how MLA achieves this with a latent bottleneck, while Kimi's Delta Attention eliminates the cache entirely in favor of a fixed-size state matrix. Part 4 looks at how models generate tokens faster without sacrificing quality. It covers Multi-Token Prediction, where the model drafts several tokens ahead using lightweight heads attached to the final hidden state, and Speculative Decoding, where those drafts are verified by the main model in a single pass. The result is roughly 2x fewer forward passes to produce the same number of tokens. The post concludes with a complete forward pass trace through the toy model to connect all the concepts. If this topic piques your interest, please check out the link in the comments. #AI #LLM #MachineLearning #DeepLearning #Transformers #AIEngineering

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