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Equation 27 · Locality Is the Whole Game: The Memory Hierarchy and What a Kernel Does Not Read

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N×NN \times N

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NN

Symbol N

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multiplication

multiplication

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Standard attention forms the score matrix S\mathbf{S} = Q\mathbf{Q}K⊤\mathbf{K}^{\top} , applies a row-wise softmax to obtain P\mathbf{P} , and multiplies by V\mathbf{V} . Both S\mathbf{S} and P\mathbf{P} are N ×\times N , and standard implementations materialise them in main memory, which is quadratic in sequence length [ 1 ] . That materialisation is the problem. It is a large intermediate, it is written and read at least once, and the operations applied to it — masking, softmax, dropout — are exactly the memory-bound kind.

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