On Friday 26 June 2015 18:03:00 Frank Reininghaus wrote: > checking the mtime frequently can have a bad effect on the performance > though if it's done incorrectly. There is a bug report about high CPU > usage in Dolphin if "sort by type" is used: > > https://bugs.kde.org/show_bug.cgi?id=346974 > > According to the backtrace, the process is busy inside > QMimeDataBase::mimeTypeForName(QString) doing time-related things and > accessing /etc/localtime all the time, probably because of the mtime > check that you mentioned. I don't know that Qt version was used > though, so I'm not sure if that still applies to the most recent > versions. > > (I cannot quite reproduce the problem though because there are other > parts of Qt's mime type handling which keep my CPU even more busy than > the time check. I should check if this still happens in recent git > snapshots of Qt and try to investigate this further...)
The mimetype code in Qt hasn't really changed, you won't get a difference by upgrading Qt. Interesting find, though. Maybe we could check the mtime only if more than N seconds have passed since the last check, but I wonder if even checking that (e.g. with QElapsedTimer) has a cost in terms of syscalls... -- David Faure, fa...@kde.org, http://www.davidfaure.fr Working on KDE Frameworks 5
