blog/data/2012-04-06-skolelinux-slowkdenfs.txt

   1 Title: Why the KDE menu is slow when /usr/ is NFS mounted - and how to fix it
   2 Tags: english, debian edu
   3 Date: 2012-04-06 22:10
   4
   5 <p>Recently I have worked on speeding up a Skolelinux installation
   6 using LTSP diskless workstations, and in the process I discovered
   7 something very surprising.  The reason the KDE menu is responding slow
   8 when using it for the first time, is due to the way KDE find
   9 application icons.  I discovered that showing the Multimedia menu
  10 would cause more than 20 000 IP packages to be passed between the LTSP
  11 client and the NFS server.  Most of these were NFS LOOKUP calls,
  12 resulting in a NFS3ERR_NOENT response.  Looking at the strace of
  13 kicker in Lenny (or plasma-desktop i Squeeze - same problem there), I
  14 see that the source of these NFS calls are access() system calls.  KDE
  15 can do hundreds of access() calls to find one icon file.  In my
  16 example, just finding the mplayer icon required around 230 access()
  17 calls.</p>
  18
  19 <p>The KDE code seem to search for icons using a list of icon
  20 directories, and the list of possible directories is large.  In
  21 (almost) each directory, it look for files ending in .png, .svgz, .svg
  22 and .xpm.  The result is a very slow KDE menu when /usr/ is NFS
  23 mounted, as showing a single sub menu result in thousands of NFS
  24 requests.  I am not the first one to discover this.  I found a
  25 <ahref="https://bugs.kde.org/show_bug.cgi?id=211416">KDE bug report
  26 from 2009</a> about this problem, and it is still unsolved.</p>
  27
  28 <p>My solution to speed up the KDE menu was to create a package
  29 kde-icon-cache that upon installation will look at all .desktop files
  30 used to generate the KDE menu, find their icons, search the icon paths
  31 for the file that KDE will end up finding at run time, and copying the
  32 icon file to /var/lib/kde-icon-cache/.  Finally, I add symlinks to
  33 these icon files in one of the first directories where KDE will look
  34 for them.  This cut down the number of file accesses required to find
  35 one icon from several hundred to less than 5, and make the KDE menu
  36 almost instantaneous.</p>
  37
  38 <p>The bug report mention that this do not only affect the KDE menu
  39 and icon handling, but also the login process.  Not quite sure how to
  40 speed up that part.</p>
  41
  42 <p>If you got feedback on this issue, please contact debian-edu (at)
  43 lists.debian.org.</p>