Thanks for the report. Could you please let us know which view mode you are using and whether you have turned on previews?

Icons, no previews.

Have you checked, whether increasing the maximum preview size helps? This can be done in Settings -> Configure Dolphin... -> General -> Previews: Maximum file size (BTW: the dialog has a little bit improved in KDE 4.5, as "Maximum file size" is not very clear).

Why should it help, I am not using previews. Anyways, 100Mb preview size didn't hellp at all.

Sorry, please ignore my comment #3: I mixed up this error-report with a similar report... 

Yes: This is already long on my TODO-list, but not easy to solve. It is not only Dolphin related, but involves very core kdelibs classes. E. g. loading /usr/bin is a kind of worst scenario, as the MIME-type for ~2000 files is unknown and must be determined by looking into the file. Of course this should not block Dolphin as done currently.

The mimetype determination is supposed to happen in a delayed manner. However it's quite easy for that to be broken, as soon as some code calls the method that determines the mimetype immediately. So I fix this bug every year or so ;)
This year, it seems the guilty code is KFileItem::overlays which calls KFileItem::isDesktopFile which calls KFileItem::determineMimeType...

#13 0x00007ffff6af62fd in KFileItem::determineMimeType (this=0x11f7310) at /d/kde/src/t/kdelibs/kio/kio/kfileitem.cpp:696
#14 0x00007ffff6afa782 in KFileItem::isDesktopFile (this=0x11f7310) at /d/kde/src/t/kdelibs/kio/kio/kfileitem.cpp:1467
#15 0x00007ffff6af7068 in KFileItem::overlays (this=0x11f7310) at /d/kde/src/t/kdelibs/kio/kio/kfileitem.cpp:822
#16 0x00007ffff6aeb2af in KDirModel::data (this=0xaaf9f0, index=..., role=1) at /d/kde/src/t/kdelibs/kio/kio/kdirmodel.cpp:686
#17 0x00007ffff76ac8ef in DolphinModel::data (this=0xaaf9f0, index=..., role=1) at /d/kde/src/t/kdebase/apps/dolphin/src/dolphinmodel.cpp:128
#18 0x00007ffff598af05 in QSortFilterProxyModel::data (this=0xaab170, index=..., role=1) at itemviews/qsortfilterproxymodel.cpp:1678
#19 0x00007ffff6b0d809 in QModelIndex::data (this=0x7fffffffb5b0, arole=1) at /d/qt/4/kde-qt-4.6/include/QtCore/../../src/corelib/kernel/qabstractitemmodel.h:398
#20 0x00007ffff6b09cd9 in KFileItemDelegate::Private::decoration (this=0xac04b0, option=..., index=...) at /d/kde/src/t/kdelibs/kio/kio/kfileitemdelegate.cpp:1095

I'll have a look at fixing it.

SVN commit 1128475 by dfaure:

Performance fix: Repair delayed mimetype determination: calling overlays should not do mimetype determination.
CCBUG: 237668


 M  +29 -18    kio/kfileitem.cpp  
 M  +8 -0      tests/kfileitemtest.cpp  


WebSVN link: http://websvn.kde.org/?view=rev&revision=1128475

It's a bit better now, but there's still a big slowdown whenever a mimetype is determined. The code in KCategorizedView::dataChanged between BEGIN and END seems to be the culprit - I wonder if this code is really needed when not using "categorized view", but just a simple icon view?

#2  0x00007ffff4480127 in QMap<QModelIndex, QSortFilterProxyModelPrivate::Mapping*>::const_iterator::operator* (this=0x7fffffffb790) at
 ../../include/QtCore/../../src/corelib/tools/qmap.h:305
#3  0x00007ffff447fb5d in QSortFilterProxyModelPrivate::create_index (this=0xbe9850, row=2950, column=0, it=...) at itemviews/qsortfilterproxymodel.cpp:170
#4  0x00007ffff447b94d in QSortFilterProxyModel::index (this=0xc14280, row=2950, column=0, parent=...) at itemviews/qsortfilterproxymodel.cpp:1606
#5  0x00007ffff43fffe6 in QCommonListViewBase::modelIndex (this=0xc11300, row=2950) at ../../include/QtGui/private/../../../src/gui/itemviews/qlistview_p.h:463
#6  0x00007ffff43fcb37 in QIconModeViewBase::doBatchedItemLayout (this=0xc11300, info=..., max=2962) at itemviews/qlistview.cpp:2735   
#7  0x00007ffff43f6e43 in QListViewPrivate::doItemsLayout (this=0xc37c70, delta=2963) at itemviews/qlistview.cpp:1717
#8  0x00007ffff43f5c71 in QListView::doItemsLayout (this=0xbe9d50) at itemviews/qlistview.cpp:1460
#9  0x00007ffff43dcf2a in QAbstractItemViewPrivate::executePostedLayout (this=0xc37c70) at ../../include/QtGui/private/../../../src/gui/itemviews/qabstractitemview_p.h:212
#10 0x00007ffff43ff96c in QListViewPrivate::rectForIndex (this=0xc37c70, index=...) at ../../include/QtGui/private/../../../src/gui/itemviews/qlistview_p.h:344
#11 0x00007ffff43f4057 in QListView::rectForIndex (this=0xbe9d50, index=...) at itemviews/qlistview.cpp:1226
#12 0x00007ffff43f0bb3 in QListView::visualRect (this=0xbe9d50, index=...) at itemviews/qlistview.cpp:561
#13 0x00007ffff5ef1ea9 in KCategorizedView::visualRect (this=0xbe9d50, index=...) at /d/kde/src/t/kdelibs/kdeui/itemviews/kcategorizedview.cpp:549
#14 0x00007ffff5ef7b22 in KCategorizedView::dataChanged (this=0xbe9d50, topLeft=..., bottomRight=...) at /d/kde/src/t/kdelibs/kdeui/itemviews/kcategorizedview.cpp:1413
#15 0x00007fffe4fb1d14 in DolphinIconsView::dataChanged (this=0xbe9d50, topLeft=..., bottomRight=...) at /d/kde/src/t/kdebase/apps/dolphin/src/dolphiniconsview.cpp:139
#16 0x00007fffe4fb3ce7 in DolphinIconsView::qt_metacall (this=0xbe9d50, _c=QMetaObject::InvokeMetaMethod, _id=0, _a=0x7fffffffc0a0) at 
/d/kde/build/t/kdebase/apps/dolphin/src/dolphiniconsview.moc:85
#17 0x00007ffff517751f in QMetaObject::metacall (object=0xbe9d50, cl=QMetaObject::InvokeMetaMethod, idx=74, argv=0x7fffffffc0a0) at ker
nel/qmetaobject.cpp:237
#18 0x00007ffff518d9a9 in QMetaObject::activate (sender=0xc14280, m=0x7ffff54eb380, local_signal_index=0, argv=0x7fffffffc0a0) at kerne
l/qobject.cpp:3286
#19 0x00007ffff51f50c9 in QAbstractItemModel::dataChanged (this=0xc14280, _t1=..., _t2=...) at .moc/debug-shared/moc_qabstractitemmodel.cpp:148
#20 0x00007ffff447a277 in QSortFilterProxyModelPrivate::_q_sourceDataChanged (this=0xbe9850, source_top_left=..., source_bottom_right=.
..) at itemviews/qsortfilterproxymodel.cpp:1154
#21 0x00007ffff447ee9d in QSortFilterProxyModel::qt_metacall (this=0xc14280, _c=QMetaObject::InvokeMetaMethod, _id=5, _a=0x7fffffffc430
) at .moc/debug-shared/moc_qsortfilterproxymodel.cpp:128
#22 0x00007ffff6f4fb91 in KDirSortFilterProxyModel::qt_metacall (this=0xc14280, _c=QMetaObject::InvokeMetaMethod, _id=30, _a=0x7fffffff
c430) at /d/kde/build/t/kdelibs/kfile/kdirsortfilterproxymodel.moc:68
#23 0x00007fffe4fbf249 in DolphinSortFilterProxyModel::qt_metacall (this=0xc14280, _c=QMetaObject::InvokeMetaMethod, _id=30, _a=0x7ffff
fffc430) at /d/kde/build/t/kdebase/apps/dolphin/src/dolphinsortfilterproxymodel.moc:68
#24 0x00007ffff517751f in QMetaObject::metacall (object=0xc14280, cl=QMetaObject::InvokeMetaMethod, idx=30, argv=0x7fffffffc430) at kernel/qmetaobject.cpp:237
#25 0x00007ffff518d9a9 in QMetaObject::activate (sender=0xbe1640, m=0x7ffff54eb380, local_signal_index=0, argv=0x7fffffffc430) at kernel/qobject.cpp:3286
#26 0x00007ffff51f50c9 in QAbstractItemModel::dataChanged (this=0xbe1640, _t1=..., _t2=...) at .moc/debug-shared/moc_qabstractitemmodel.cpp:148
#27 0x00007ffff6afde2c in KDirModel::itemChanged (this=0xbe1640, index=...) at /d/kde/src/t/kdelibs/kio/kio/kdirmodel.cpp:635
#28 0x00007ffff6f7e133 in KFilePreviewGenerator::Private::dispatchIconUpdateQueue (this=0xbf5290) at /d/kde/src/t/kdelibs/kfile/kfilepreviewgenerator.cpp:709
#29 0x00007ffff6f80db2 in KFilePreviewGenerator::qt_metacall (this=0xc4b2d0, _c=QMetaObject::InvokeMetaMethod, _id=5, _a=0x7fffffffc6a0
) at /d/kde/build/t/kdelibs/kfile/kfilepreviewgenerator.moc:98

Thanks a lot David for your investigations, I'll check the code in KCategorizedView::dataChanged() today in the evening. I'm very, very sure, that this code is only needed if the categorized view has been enabled.

OK, thanks. Thinking about it further, though, the time is spent in the re-layout of listview items after dataChanged was emitted, it would happen later on even if this code was not there, I think. Still worth cleaning up, but it might not have much effect on performance.

Breaking into the process later on I saw much time spent in
KIconEngine::actualSize, which currently loads the actual icon just to find its
size. I'll make a reviewboard request for that one.

http://reviewboard.kde.org/r/4052/

SVN commit 1128571 by ppenz:

Performance optimization: Check whether the categorization feature is used, before adjusting categorization specific properties

CCBUG: 237668

 M  +13 -2     kcategorizedview.cpp  


WebSVN link: http://websvn.kde.org/?view=rev&revision=1128571

@David: I've applied your patch from http://reviewboard.kde.org/r/4052/ locally and it seems to work great :-) If I'd see any icon size specific issues, I'd let you know.

I verified this issue now with KDE SC 4.5.0 and loading /usr/bin, /usr/lib is very fast now.