title: Reduce cpu cost of readyRead() when using high speed internet connection
body: <p>I tried to profiling my program, which is a file downloader. I use 5 <code>QNetworkRequest</code> to enhance transfer speed, they all connect to the same  <code>readyRead()</code> slot.</p>
  
  <p>I use QMap to buffer those byte arrays.</p>
  
  <p>When downloading speed reaches, e.g 5 MiB/s, I found CPU costs rises up significantly, nearly 100%, <code>readyRead()</code> was calling 30 times per seconds.</p>
  
  <p>Is there any suggestion to this, e.g can I let QNetworkReply buffer its io device, reduce the amount of signals emitted?</p>
  
  <p><strong>UPDATA</strong></p>
  
  <p>I made some debug output in readyReady():
  (<code>reply</code> here was casted from sender())</p>
  
  <p><code>qDebug() &lt;&lt; "Got: " &lt;&lt; reply-&gt;readAll().length() &lt;&lt; " bytes";</code></p>
  
  <p>And about 30 output per seconds , each contains 1500 bytes</p>