>extensive manual tuning I was surprised by how little low-level knowledge it took to get within a stone's throw of the theoretical peak. The general rule see

>extensive manual tuning I was surprised by how little low-level knowledge it took to get within a stone's throw of the theoretical peak. The general rule seems to be: - keep data in packed registers (use YMM instead of XMM if you have them) - interleave addition and multiplication - unroll the loop sufficiently to avoid stalls I wonder if how close to ATLAS you could get if you wrote a matrix multiply following these principles and additionally structured the row/column iterations into cache-sized tiles.