Intel shows a 27x speedup in matrix multiplication by just swapping two loops, both O(n³)

jedisct1 · x · 2026-09-09

Intel demonstrated that in a matrix multiplication example, simply swapping the nesting order of two loops — with both versions remaining O(n³) — yields a 27x speedup.

The takeaway: the real bottleneck is usually memory access order rather than arithmetic. Cache-friendly data traversal beats days spent optimizing the math, a lesson relevant to anyone doing high-performance or inference optimization.

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