[sitkack]

AVX2 also incurs some pretty large penalties for switching between SSE and AVX2. Depending on the amount of time taken in the library between calls, it could be problematic.

This looks mostly applicable to server scenarios where the runtime environment is highly controlled.

[BeeOnRope]

There is no real penalty for switching between SSE and AVX2, unless you do it wrong. What are you referring to specifically?

Are you talking about state transition penalties that can occur if you forget a vzeroupper? That's the only thing I'm aware of which kind of matches that.