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List:       kde-optimize
Subject:    Re: Mimetype optimization
From:       David Faure <faure () kde ! org>
Date:       2008-04-22 20:36:09
Message-ID: 200804222236.10663.faure () kde ! org
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On Tuesday 22 April 2008, Jakub Stachowski wrote:
> Hello,
> 
> profiling dolphin while opening /usr/bin shows that about 35% of time is spent 
> in QRegExp matching called by kmimefactory.cpp: matchFileName. This function 
> already contains optimizations: for some simple (but popular) patterns like 
> *.something or something* it uses direct comparision instead of QRegExp big 
> gun. It looks like:
>    if (pattern like *.something && filename long enough to match the pattern)  
> compare directly;. 
> However for short names (lots of them in /usr/bin) it often falls back to slow 
> path. Attached patch changes is to:
> if (pattern like *.something) { 
> 	if (filename not long enough to match) return false;
> 	else compare directly;
> }
> 
> and detects patterns without wildcards (is checking for *,? and ] enough?)
> 
> Results (measured by callgrind):
> Unpatched, for 179 calls to KMimeTypeFactory::findFromFileName
> - 5554 calls to QRegExp::exactMatch, which accounts for 35% of CPU time
> 
> Patched,  for 150 calls to KMimeTypeFactory::findFromFileName
> - QRegExp matched 13 times.  findFromFileName takes 0.67% of CPU time

Wow, excellent. Great find.
If the kdecore/tests/kmimetypetest unit test still passes, please commit :)

-- 
David Faure, faure@kde.org, sponsored by Trolltech to work on KDE,
Konqueror (http://www.konqueror.org), and KOffice (http://www.koffice.org).
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