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(Updated June 6, 2014, 11:28 a.m.) Review request for kdelibs, David Faure, Matthew Dawson, and Oswald Buddenhagen. Changes ------- use friend functions Repository: kdelibs Description ------- Optimize KConfigIniBackend::parseConfig by reducing allocations. Yet another awesome application of the Qt implicit sharing trick. Since config files often contain only few different keys and even value strings, we can share them. This reduces memory consumption and also speeds up parsing, as we do not have to allocate the duplicated strings, but can simply reuse the previous values. The most extreme case for this of my knowledge, is KatePart: katesyntaxhighlightingrc has more then 20k lines which triggered about 30k allocations on startup. With this patch applied, this value goes down dramatically. I added a simple static counter for the cache hit/miss ratio, which resulted in 5442 cache misses compared to 43624 cache hits across all KConfig files parsed by kwrite on startup. Diffs (updated) ----- kdecore/config/bufferfragment_p.h 5a753ad kdecore/config/kconfigini.cpp 8ec43c5 kdecore/config/kconfigini_p.h d7aa43e Diff: https://git.reviewboard.kde.org/r/118587/diff/ Testing ------- Unit tests all pass. My malloc tracer shows that the allocations are all gone. My malloc tracer showed before: 17421 allocations at: 0x7fee73692b97 QByteArray::QByteArray(char const*, int) /usr/lib/libQtCore.so.4 0x7fee73bb7cee ? /usr/lib/libkdecore.so.5 0x7fee73bb7fc4 ? /usr/lib/libkdecore.so.5 0x7fee73ba1320 ? /usr/lib/libkdecore.so.5 0x7fee73ba1731 KConfig::KConfig(QString const&, QFlags<KConfig::OpenFlag>, char const*) /usr/lib/libkdecore.so.5 0x7fee64830c06 KateHlManager::KateHlManager() in /ssd/milian/projects/kde4/kate/part/syntax/katesyntaxmanager.cpp:76 /ssd/milian/projects/compiled/kde4/lib/libkatepartinterfaces.so.4 12699 allocations at: 0x7fee73692b97 QByteArray::QByteArray(char const*, int) /usr/lib/libQtCore.so.4 0x7fee73bb7cd7 ? /usr/lib/libkdecore.so.5 0x7fee73bb7fc4 ? /usr/lib/libkdecore.so.5 0x7fee73ba1320 ? /usr/lib/libkdecore.so.5 0x7fee73ba1731 KConfig::KConfig(QString const&, QFlags<KConfig::OpenFlag>, char const*) /usr/lib/libkdecore.so.5 0x7fee64830c06 KateHlManager::KateHlManager() in /ssd/milian/projects/kde4/kate/part/syntax/katesyntaxmanager.cpp:76 /ssd/milian/projects/compiled/kde4/lib/libkatepartinterfaces.so.4 These where the allocation hotspots number #1 and #3 respectively. With the patch applied, the two locations are not under the top 10 anymore. Thanks, Milian Wolff
