title: Drupal ob_flush() slow and variable performance
body: <p>After profiling Drupal site using XHProf. I am seeing variable performance of ob_flush() call which is called only once per page.</p>
  
  <p><strong>First load Page x</strong></p>
  
  <blockquote>
  <pre><code>Function   Calls  Ex Wall  Wall %
  ob_flush   1      1,712ms  39.5%
  </code></pre>
  </blockquote>
  
  <p><strong>Second load Page x</strong></p>
  
  <blockquote>
  <pre><code>Function   Calls  Ex Wall  Wall %
  ob_flush   1      270ms    24.5%
  </code></pre>
  </blockquote>
  
  <p><strong>Third load Page x</strong></p>
  
  <blockquote>
  <pre><code>Function   Calls  Ex Wall  Wall %
  ob_flush   1      300ms      25.3%
  </code></pre>
  </blockquote>
  
  <p>In php.ini settings I have disabled out_buffering = 0 as seems to be suggestion for Drupal</p>
  
  <p>I see other <a href="https://stackoverflow.com/questions/13903970/ob-flush-takes-long-time-to-be-executed">queries</a> on this which don't provide a clear solution.</p>
  
  <p>Is there a way to improve this performance?</p>