Re: bring speed back into KConfig

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Dnia wtorek, 15 kwietnia 2008, Dirk Mueller napisa=C5=82:
> Hi,
>
> the "knotify4 eats cpu" bugreport seems to be highly popular, so the reas=
on
> for that seems to be the incredible performance loss in KConfigIni  due to
> the "kconfig refactoring branch" being merged last autumn by Andreas
> Pakulat.
>
> The code now uses highlevel QByteArray operations=20

Lots of reallocations and memory copies instead of simple moving of pointer.

> and even worse QFile=20
> operations for operating on the .ini files. My testcase of kwin.notifyrc,
> this means:

Attached very simple patch cuts parsing time by ~50% (on hot cache). It rea=
ds=20
whole config file in one go, like KDE3 did.
KDE3 also was able to mmap() file instead of reading it, but readAll() show=
s=20
5% on profile (using google perftools) so there are still many bigger=20
targets.

>
> 2000 lines of config
>
> resulting in
>
> 16000 ~QByteArray() and 16000 QByteArray() constructions
> 6000 syscalls (stat() and 2x llseek()) due to QFile::readLine and
> QFile::atEof()
> 8000 memcpy operations
>
> in time:
>
> 150ms KConfig4
> 45ms  via QSettings of Qt 4.4
> 29ms via KConfig3
>
> I think thats a bit under performing. Anyone interested in fixing the hot
> spots in that code? I think it is fairly obvious why the code is extremely
> slow. I wanted to take a look at it myself but I guess I'll run out of ti=
me
> before I get anywhere.
>
> Thanks,
> Dirk
> _______________________________________________
> Kde-optimize mailing list
> [email protected]
> https://mail.kde.org/mailman/listinfo/kde-optimize

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Index: kconfigini.cpp
===================================================================
--- kconfigini.cpp	(wersja 797091)
+++ kconfigini.cpp	(kopia robocza)
@@ -89,8 +89,9 @@
     bool groupSkip = false;
 
     int lineNo=0;
-    while (!file.atEnd()) {
-        QByteArray line = file.readLine().trimmed();
+    QList<QByteArray> lines=file.readAll().split('\n');
+    Q_FOREACH(QByteArray line, lines) {    
+        line=line.trimmed();
         lineNo++;
 
         // skip empty lines and lines beginning with '#'

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