FlashAttention Illustrated — From Hardware to Computation Logic
In-depth visual guide to FlashAttention V1 covering GPU memory hierarchy, tiling strategies, IO-aware algorithms, and exact attention computation.
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FlashAttention Illustrated
FlashAttention is an IO-aware exact attention algorithm that runs 2-4x faster by optimizing GPU memory access.
The Problem
Standard attention materializes the N x N matrix in HBM, causing O(N^2) memory bottlenecks.
The Solution
FlashAttention tiles computation to fit in GPU SRAM, recomputes attention during backward pass to avoid materialization, achieving 2-4x speedup. This enabled 32K+ context windows in modern LLMs.
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