4 ms·

You're confusing MSRs (which don't have to be saved/restored on context switch) with GPRs (which do).

• saagarjha 5y ago
  Apple reserves certain MSRs that apply on a per-process basis, and thus must be applied on context switch.
• ithkuil 5y ago
  Well if there is a truly undocumented extension, how do I know it doesn't come with it's own registers (e.g. like a floating point unit does)