When the first AVX instruction is run after a long period of no AVX, something like this does happen: the dispatch of instructions is throttled to 1 out of 4 cy

When the first AVX instruction is run after a long period of no AVX, something like this does happen: the dispatch of instructions is throttled to 1 out of 4 cycles while some AVX instruction is in the scheduler (this applies to all instructions, not just AVX). This is severe restriction: even if could be limited to AVX instructions, running at 25% of the throughput would make AVX pretty useless. This state persists only for a short time until a voltage and possibly frequency transition can be made at which point everything can run at full speed (albeit sometimes at a reduce frequency).