title: Python multiprocessing.Pool() doesn't use 100% of each CPU
body: <p>I am working on multiprocessing in Python.
  For example, consider the example given in the Python multiprocessing <a href="http://docs.python.org/2/library/multiprocessing.html#using-a-pool-of-workers" rel="noreferrer">documentation</a> (I have changed 100 to 1000000 in the example, just to consume more time). When I run this, I do see that Pool() is using all the 4 processes but I don't see each CPU moving upto 100%. How to achieve the usage of each CPU by 100%?</p>
  
  <pre><code>from multiprocessing import Pool
  
  def f(x):
      return x*x
  
  if __name__ == '__main__':
      pool = Pool(processes=4)            
      result = pool.map(f, range(10000000))  
  </code></pre>