What makes you think doing unwinding in userspace would do any more context switches (by which I think you mean privilege level transitions) than we do today? S

What makes you think doing unwinding in userspace would do any more context switches (by which I think you mean privilege level transitions) than we do today? See my other comment on the subject. > Things get even more complicated because context switches can mean CPU migrations, making many of your data useless. No it doesn't. If a user space thread is blocked on doing kernel work, its stack isn't going to change, not even if that thread ends up resuming on a different thread.