D10857: Change qSort to std::sort in simplifiedUrlList

[Mark Gaiser]

markg added a comment.


  In D10857#214867 <https://phabricator.kde.org/D10857#214867>, @jtamate wrote:
  
  > In D10857#214607 <https://phabricator.kde.org/D10857#214607>, @dfaure wrote:
  >
  > > I'm not opposed to the idea, but measuring CPU usage is a rather misleading indicator. What if it takes 10 times longer, because it's progressing much more slowly? ;)
  > >
  > > Please at least measure with QElapsedTimer around the sorting (not to be committed, just to gather numbers about the actual performance of this from a user's point of view).
  > >  I'm interested in the result ;)
  >
  >
  > The results are strange. All the results are measured sorting 50.000 small files:
  >
  > Both Qt are the same version from opensuse.
  >
  > In an i5, why the difference is so big? recent cpu bugs?
  >  qSort in i3 
  >  274764, 276060 (with 3 directories), 365878, 424506  (without directories)
  >  std::sort in i3
  >  940, 995 (with 3 directories), 2472, 2539 (without directories)
  >
  > In AMD the results are closer, qSort wins
  >  qSort in AMD
  >  658, 726, 695, 683, 676, 666, 649, 684, 666 (without directories)
  >  std:sort in AMD
  >  843, 839, 878, 896,  925 (without directories)
  
  
  That surprises me a lot!
  I "thought" qSort was just a template or alias to std::sort, but it isn't: http://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/tools/qalgorithms.h#n340
  But it isn't which kinda makes my other expectations moot (qSort == std::sort... it isn't)
  
  So i did some tests as well.
  50000 filenames sorting them (computer sorting, not the natural one) with std::string and QString (yes, it matters)
  Filenames, well, sorta.. Made them up in a loop :)
  
  QString version: https://p.sc2.nl/r1JTFaf_z
  qSort: ~220ms
  std::sort ~276ms
  
  std::string version: https://p.sc2.nl/HJ69Y6G_G
  qSort: ~100ms
  std::sort ~130ms
  
  Note that std::string might not be the fair comparison as it's 8 bit/char. QString is 16.
  My compiler (in this rare case) Visual Studio 2017 on an Intel CPU.
  
  I still think it's wise to replace all qSort, if only for it being deprecated. But it does suck a little that qSort beats std::sort.

REPOSITORY
  R241 KIO

REVISION DETAIL
  https://phabricator.kde.org/D10857

To: jtamate, #frameworks, dfaure
Cc: markg, apol, michaelh
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