Do you know the difference between kernel and user threads?

Do threads run at the user level or the kernel level provide greater performance? Explain the key differences between threads at the user level and those at the kernel level. Can there possibly be an instance when one variety trumps another?

Do user-level threads have any benefits over kernel-level threads? How different are threads created by the user and those created by the kernel? Is there ever a time when one kind would be better than the other?

What distinguishes threads at the user level from those in the kernel? Just when does one kind perform better than the other?