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Published equation contexts

3N23N^2

Why this formula appears here

Matrix multiplication is the canonical demonstration because it has enormous latent reuse and a naive schedule that throws almost all of it away. Multiplying two N ×\times N matrices performs about 2N3N^3 operations on 3N2N^2 words — an intensity proportional to N , which for large N is spectacularly compute-bound in principle. Executed as three nested loops in the obvious order, though, each element of one input is re-read from main memory on every pass, and the realised intensity collapses toward a small constant. The available reuse and the exploited reuse are different quantities, and only the second appears in the roofline.

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3N23N^2

Equation 12 · AI Hardware & Semiconductors

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

This mathematical expression combines the displayed quantities; its precise role follows from the surrounding article text.

Matrix multiplication is the canonical demonstration because it has enormous latent reuse and a naive schedule that throws almost all of it away. Multiplying two N ×\times N matrices performs about 2N3N^3 operations on 3N2N^2 words — an intensity proportional to N , which for large N is spectacularly compute-bound in principle. Executed as three nested loops in the obvious order, though, each element of one input is re-read from main memory on every pass, and the realised intensity collapses toward a small constant. The available reuse and the exploited reuse are different quantities, and only the second appears in the roofline.

Meanings in this article

  • N2N^2: the square of N; spectacularly compute-bound in principle.
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