I wrote about the performance of KDE 4 some time ago, and I'd like to revisit it.
After a few threads about debug builds and release builds on kde-core-devel I figured I was wrong in my previous entry, KDE 4 couldn't easily be build without debugging symbols. So my build WAS a debug build. But now it's possible to have it clean and fast, and I did indeed see an increase in performance when trying it.
Apps start up even faster, it's rather weird to see an application which always took a noticeable delay to start up now pop up like its a basic calculator ;-)
Drawing is also a bit faster, but still clearly not as fast as in KDE 3. Resizing dolphin on KDE 3 is almost entirely smooth - very unlike the rather unpleasant experience on KDE 4. Gwenview is a bit faster, it doesn't draw an image visibly when you drag it anymore but clearly isn't as smooth as the KDE 3 version. It IS faster loading large images though, a 6400x3200 image loaded in a snap (!) while the KDE 3 gwenview made me think it got stuck...
And here's a new Konqi-auto-scrolling picture. It starts with XPLANET (nice 20, yes), then 5 seconds pause, and I start scrolling the Konqi from KDE 3. You don't see a visible difference in CPU usage... When I increase the speed of the scrolling, there are some very small spikes but generally the CPU is still barely used.
The picture for KDE 4 is different - approximately 10% of my cpu is needed to scroll a page slowly, which increases to 20% when I increase the speed of scrolling.
Notice that these numbers DO represent a decrease compared to my previous test, which showed twice as high CPU usages in KDE 4. So it might be no more debugging, or some performance work - either way, Konqi got twice as fast already ;-)
As discussed on the other blog post, this is all with a dualcore 2.4 ghz AMD, 3 gb ram, proprietary NVidia drivers (geforce 6600) and NO compositing. Tests are run in a KDE 3 environment. Yes, double-buffering is on in Qt4 - as it should be, it looks horrible without... The whole area flashes when scrolling.
One person mentioned a potential scrolling bug in Qt4, which makes it redraw the whole area when scrolling. This could indeed explain the flickering without double-buffering and the performance problems, I guess. Hopefully a new Qt version fixes this, I found quite a few scroll-speed related bugs in the TT bugtracker.
I think I can conclude the performance issues with drawing are not as bad as I depicted in my previous blog, and it's very well possible they can and will be fixed. Meanwhile, KDE 4 performs amazingly well in many other areas - most noticeably application startup.
EDIT: With some help (see comments) I was able to compile QtCurve for KDE 4, and tried it. Some argued the slow drawing when resizing might be due to Oxygen behing slow, and that showed indeed at least half true. Dolphin resizes faster with Qtcurve - but the KDE 3 version is still much more smooth.