Bug 213708

Version:            (using KDE 4.3.3)
Compiler:          gcc (Gentoo 4.4.2 p1.0) 4.4.2 
OS:                Linux
Installed from:    Gentoo Packages

Whenever the slideshow desktop wallpaper changes the wallpaper, the entire system comes to grinding halt for a second or two.  It is as though decoding and/or scaling the new wallpaper are being done in a very high-priority thread, and everything else has to wait.  Even keyboard input queues up and is only processed by the foreground application after the wallpaper changes.

If it matters, I am using a single 2560x1600 monitor on an NVIDIA GeForce 8600 GT (PCI-E 16x, 256 MB) with the 190.42 NVIDIA proprietary driver.  My wallpapers are typically 1920x1200 or 2560x1600 JPEGs that are 0.5 to 2 MB in size, so decoding and potentially scaling them is not a trivial computational task.  I have compositing enabled in X and in KWin.

An interesting note is that a completely independent X.org X11 server instance (a separate X process running on a different virtual terminal, with only MPlayer as a client, no KDE at all, not even KWin) suffers from the same periodic, momentary hang caused by the wallpaper changing in the first X instance.  This leads me to believe it's not a problem in the X server, since the second, independent X process is also affected by the wallpaper changing.

Could the wallpaper change be done in a lower-priority thread so as not to disrupt system responsiveness?  It doesn't really matter if it takes several seconds to render the new wallpaper if I don't notice it happening.  At present, I definitely notice it because everything stops responding briefly.