title: 'perf top' command doesn't run properly on virtual machine
body: <p>I got a virtual machine running Ubuntu 12.04 with linux kernel 3.2.0-31. When I try to run the <code>sudo perf top</code> command, which can profile the entire system's processes and gather their information, none of the information shows up. But other commands runs fine, like <code>perf stat ls</code> that collects all performance info running ls command.</p>
  
  <p><img src="https://i.stack.imgur.com/o2YZS.png" alt="screenshot"> </p>
  
  <p>So I am wondering : is that because <code>perf top</code> command does not support virtual machine? Any ideas?</p>