title: Why does function takes zero seconds to execute
body: <p>I have written the following code where I average the rows of a frame. I wanted to test the speed and compare it with using <code>np.mean</code>.</p>
  <pre><code>@jit(nopython=True)
  def test(frame):
      #np.mean(frame, axis=1)
      
      averages = []
      for i in range(480):
          summation = 0
          for j in range(640):
              summation += frame[i, j, 1]
  
          averages.append(summation/640)
      return averages
  
  while True:
       a = time.time()
       test(frame)
       print(&quot;My program took {:.15f} seconds to run&quot;.format(time.time() - a))
  </code></pre>
  <p>When using <code>np.mean()</code>, I get average time around 6ms. When I remove it and use numba, the first iteration takes 100ms, but the subsequent take 0.000000000s. I want to know the exact speed of the code when using numba, because I am certain it doesn't take 0s to execute the code.</p>