title: usleep busy waiting
body: <p>started to experience with some real time threads.
  I just sent my thread to sleep by calling usleep(TIME).
  This will guarantee the thread to sleep for at least TIME.
  I now measured with TIME= 10ms and got a gaussian function with an expected value of µ=10,1ms
  The second measuring with TIME = 1us: I get a big peak at 4us.</p>
  
  <p>So why is the second measurement not gaussian? My first idea was, the thread does not really sleep, but it makes a busy waiting instead. As stated <a href="http://kernel.org/doc/man-pages/online/pages/man2/nanosleep.2.html" rel="nofollow">here (old beahavior)</a> there is no busy waiting. How can one explain the two curves?</p>