title: Many-to-one mapping of user threads to a kernel thread
body: <p>As I understand it, in many-to-one mapping, one kernel thread manages many user threads. This kernel thread helps the user threads make system calls etc. What I don't understand is:</p>
  
  <ol>
  <li>Why do we have many-to-one mapping if a single blocking call would
  block all user threads managed by the kernel thread ?</li>
  <li>In many-to-one mapping of user threads to a kernel thread, do all the
  user threads have to be from the same process ?</li>
  <li>In many-to-one mapping, can all the user threads be run on different
  cores/CPUs at once or is only one of them run at a time ?</li>
  </ol>