title: Demistifying iOS device CPU usage
body: <p>My app use CPU so it drain battery really quick. 
  I'm trying to detect what is using CPU with instruments. 
  I'm running counters and i/o events but can't understand information I recieved. In counters I see only dispatch_mgr_thread at the first place. I'm hiding system libraries and have [UIApplication run] -> method from app in call three. 
  Is that method the reason of CPU usage?</p>
  
  <p>UPD: I've also checked app with time profiler and here is the result:
  <img src="https://i.stack.imgur.com/XRCwj.png" alt="enter image description here"></p>
  
  <p>And I don't understant what is this "_dispatch_mgr_thread" or "_dispatch_worker_thread3" that works the mostly in my app even while I don't push any bottons - just start app and it does nothing.</p>