What is the speedup compared against? Is it compared against non-avx code? Or is it compared against avx2 (256-bit)? From my experience, vectorizing with avx

What is the speedup compared against? Is it compared against non-avx code? Or is it compared against avx2 (256-bit)? From my experience, vectorizing with avx2 can speed up 3x-10x against non-avx operations depending on the data. The operations involved are things like finding common prefix or searching in string.