title: Limit total CPU usage in python multiprocessing
body: <p>I am using multiprocessing.Pool.imap to run many independent jobs in parallel using Python 2.7 on Windows 7. With the default settings, my total CPU usage is pegged at 100%, as measured by Windows Task Manager. This makes it impossible to do any other work while my code runs in the background.</p>
  
  <p>I've tried limiting the number of processes to be the number of CPUs minus 1, as described in <a href="https://stackoverflow.com/questions/5495203/how-to-limit-the-number-of-processors-that-python-uses">How to limit the number of processors that Python uses</a>:</p>
  
  <pre><code>pool = Pool(processes=max(multiprocessing.cpu_count()-1, 1)
  for p in pool.imap(func, iterable):
       ...
  </code></pre>
  
  <p>This does reduce the total number of running processes. However, each process just takes up more cycles to make up for it. So my total CPU usage is still pegged at 100%.</p>
  
  <p>Is there a way to directly limit the total CPU usage - NOT just the number of processes - or failing that, is there any workaround?</p>