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6 <title>Petter Reinholdtsen: Why the KDE menu is slow when /usr/ is NFS mounted - and a workaround</title>
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14 <h1>
15 <a href="http://people.skolelinux.org/pere/blog/">Petter Reinholdtsen</a>
16
17 </h1>
18
19 </div>
20
21
22 <div class="entry">
23 <div class="title">Why the KDE menu is slow when /usr/ is NFS mounted - and a workaround</div>
24 <div class="date"> 6th April 2012</div>
25 <div class="body"><p>Recently I have spent time with
26 <a href="http://www.slxdrift.no/">Skolelinux Drift AS</a> on speeding
27 up a <a href="http://www.skolelinux.org/">Debian Edu / Skolelinux</a>
28 Lenny installation using LTSP diskless workstations, and in the
29 process I discovered something very surprising. The reason the KDE
30 menu was responding slow when using it for the first time, was mostly
31 due to the way KDE find application icons. I discovered that showing
32 the Multimedia menu would cause more than 20 000 IP packages to be
33 passed between the LTSP client and the NFS server. Most of these were
34
35 NFS LOOKUP calls, resulting in a NFS3ERR_NOENT response. Because the
36 ping times between the client and the server were in the range 2-20
37 ms, the menus would be very slow. Looking at the strace of kicker in
38 Lenny (or plasma-desktop i Squeeze - same problem there), I see that
39 the source of these NFS calls are access(2) system calls for
40 non-existing files. KDE can do hundreds of access(2) calls to find
41 one icon file. In my example, just finding the mplayer icon required
42 around 230 access(2) calls.</p>
43
44 <p>The KDE code seem to search for icons using a list of icon
45 directories, and the list of possible directories is large. In
46 (almost) each directory, it look for files ending in .png, .svgz, .svg
47 and .xpm. The result is a very slow KDE menu when /usr/ is NFS
48 mounted. Showing a single sub menu may result in thousands of NFS
49 requests. I am not the first one to discover this. I found a
50 <a href="https://bugs.kde.org/show_bug.cgi?id=211416">KDE bug report
51 from 2009</a> about this problem, and it is still unsolved.</p>
52
53 <p>My solution to speed up the KDE menu was to create a package
54 kde-icon-cache that upon installation will look at all .desktop files
55 used to generate the KDE menu, find their icons, search the icon paths
56 for the file that KDE will end up finding at run time, and copying the
57 icon file to /var/lib/kde-icon-cache/. Finally, I add symlinks to
58 these icon files in one of the first directories where KDE will look
59 for them. This cut down the number of file accesses required to find
60 one icon from several hundred to less than 5, and make the KDE menu
61 almost instantaneous. I'm not quite sure where to make the package
62 publicly available, so for now it is only available on request.</p>
63
64 <p>The bug report mention that this do not only affect the KDE menu
65 and icon handling, but also the login process. Not quite sure how to
66 speed up that part without replacing NFS with for example NBD, and
67 that is not really an option at the moment.</p>
68
69 <p>If you got feedback on this issue, please let us know on debian-edu
70 (at) lists.debian.org.</p>
71
72 <p>Update 2015-08-04: The
73 <a href="http://anonscm.debian.org/cgit/debian-edu/upstream/kde-icon-cache.git/">source
74 of the scripts and associated Debian package</a> is available from the
75 Debian Edu github repository.</p>
76 </div>
77
78 <div class="tags">Tags: <a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu</a>, <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>.</div>
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