My home machine, as I’ve said before, runs Bluewhite64 with KDE4.1.3, it’s basically a bit of a preview of what Kongoni is being built from. My work laptop however runs Kubuntu Intrepid also with KDE4.1.3. Now overall I’m actually quite happy with this kubuntu release, it’s certainly the first one that shows polish even remotely comparable to it’s gnome counterpart so that’s a good thing.
Unfortunately, it has one seriously annoying bug. Selecting and dragging text in firefox is a CPU killer, I know this is neither a firefox nor a kubuntu bug since the problem doesn’t exist on my home machine. It’s something specific to this machine, or this release of Kubuntu.
What happens ? Well select some text and drag it – you don’t even need to drop it anywhere – just letting go of the mouse is enough, the system freezes while the CPU works incredibly hard for several minutes and then finally drops the text (if you didn’t drop it somewhere else, back where it was) before returning to normal.
During this time, the rest of the system is completely unresponsive, you can see the text moving incredibly slowly over the path the mouse followed before finally dropping and then the system recovers. Now just why exactly this is slow I haven’t been able to figure out conclusively – but I have a theory.
This machine, unlike the home machine, has full XRandR1.2 support and really good XRender support, and I think firefox is using XRender to draw the text when it’s being dragged – and I think it’s buggy with the way it does that. It doesn’t happen at home because nvidia’s xrender support sucks so bad that firefox doesn’t even try to use it. But if firefox is using it this badly – it would have been better not to use it at all.
So by my theory, the problem is with firefox on intel graphics cards that support full XRender. By that logic – the problem needs to be fixed either in firefox or in the i915 driver. Since both are FOSS code – this should be doable. Hence my decision to post it here. It would be good to know if anybody has similar problems, and on what video cards – if it’s happening for you on something that doesn’t support XRender then it suggests the problem is confined to firefox, if it happens for you in other apps – it means it’s something at library level in Kubuntu. The most likely combinations are similar hardware but other apps, same apps on different hardware or same apps on same hardware. Getting some feedback on which scenario’s are out there will help track down who to file a bug report with at least.
