Is stopping the GC on some objects with sb-sys:with-pinned-objects a
costly operation in itself? (on Linux, X86, if I need to be specific).
I can't benchmark it separately (I always get zero/immeasurably small
time if I do nothing in the body, maybe the compiler is very smart?).
An intuitive feel would be good enough, eg "this is a very cheap
operation, just setting a few bits", or "this is a major thing for the
gc, don't do it 30 times in a simple function call".