title: GNU parallel: does -k (keep output order) affect speed?
body: <p>As said in the title, I'm wondering if the <code>-k</code> option (strongly) affects the speed of GNU parallel.</p>
  
  <p>In <code>man parallel_tutorial</code> there is a discussion about <code>--ungroup</code> and <code>--line-buffer</code>, which claims that <code>--linebuffer</code>, which unmixes output lines, is much slower than <code>--ungroup</code>. So maybe <code>-k</code> will also result in major slowdown when the job count is large?</p>
  
  <p>(I didn't find this topic in <code>man parallel</code> or <code>man parallel_tutorial</code>; neither did I find anything with some Google. I haven't finished <code>man parallel</code> though, so if I missed something with less search, please excuse me.)</p>