Monday, February 22, 2010


Although I like Criminal Minds, this blog entry is less thrilling: it's about profiling applications like Dolphin.

When I faced a performance issue in Dolphin, I usually used valgrind in combination with callgrind to find the bottleneck (valgrind --tool=callgrind dolphin -nofork). The output can be visualized by KCacheGrind in a nice way:

One big benefit of Valgrind is that it gives 100 % coverage of user-space code. But as usual there are rarely benefits without drawbacks: As valgrind is a kind of virtual machine, that uses just-in-time compiling, the application runs around 5 times slower. This can get a problem if timers are involved in the application. Also performance issues in combination with threads are tricky to identify, because valgrind does not give a non-obtrusive performance overview of the overall system.

So I started to get familiar with OProfile during the last week. OProfile is a non-obtrusive system-wide profiler, which means that the application runs (nearly) at the same speed as without profiler. OProfile gives an overview about the workload of all processes in the system. This is very useful for Dolphin, as the overall performance of Dolphin depends also on e. g. Nepomuk and asynchronous operations to e. g. get file previews. It is possible to convert the OProfile output to a readable KCachegrind file by 'opreport -gdf | op2calltree'.

Dependent on the usecase, both tools are really helpful. The next thing on my TODO-list is to get more familiar to locate I/O bound bottlenecks: When reading the number of sub directories for 20000 directories, the bottleneck is definitely not on the CPU side (in this case neither Valgrind nor OProfile can detect the bottleneck). All in all I hope that I find the time during the KDE SC 4.5 cycle to improve the Dolphin performance in some areas with the help of these tools.

Monday, February 15, 2010

Visiting Openismus in Berlin

On February the 1st I started my new job at Openismus. Most of the time I can work at home in Austria, but last Wednesday I got the chance to meet the Openismus team at their office in Berlin. Beside my first visit of Openismus, it was also my first visit of Berlin. I was very impressed by both of them: the team and Berlin.

I got the chance to do some trials with Qt on Maemo and to get familiar with what is working well and which parts still need a lot of investigations. All developers at Openismus are Gnome people, being the only one using KDE is not always easy ;-) But maybe it helped that Dolphin does not look so much different in comparison to Nautilus - I even got a KDE-sticker from an Openismus colleague.

I'm learning a lot of new stuff currently and will have less time during the next weeks for Dolphin. However this will change after mastering the usual time that is needed to get really productive. In the end I hope that I can apply the knowledge I gathered through KDE development with Dolphin for Openismus and also that Dolphin will benefit from the new things I learn at Openismus.