Dual 4K slowness due to xorg threading concept?

[Thomas Wunder]

On Freitag, 2. Oktober 2015 07:23:57 PDT, Thomas Lübking wrote:
> On Freitag, 2. Oktober 2015 12:59:30 CEST, Christopher Barry wrote:
> >> Problem:
> >> "Graphics stuff" seems to work smoothly on lower resolutions (e.g. 2x
> >> 2560x1600). On high resolution (2x 3840x2160) still everything
> >> (moving/resizing windows, playing videos, scrolling through lists,
> >> text views or consoles, opening menus) goes smoothly but only as long
> >> as single windows are really small (and as long as there are not too
> >> many of them). As soon as a window becomes half the size of a screen
> >> or even full screen, operations mentioned before become horribly slow
> >> (K-Menu takes up to 8 secs to even open up) and CPU usage of the Xorg
> >> process is vastly increasing (to about 100%). I don't really have an
> >> idea of what's going wrong here. There are no apparent errors etc.
> >> The only thing that seems really suspect to me is the 100% CPU which I
> >> would attribute to a (multi-)threading issue... I'd really appreciate
> >> if you could give me a hand and point me to the right direction to get
> >> things working.
> 
> You're likely running into texture/shader limitations and fallover to some
> software emulation - the GPU is indeed not fully suited for such
> resolutions.
> 
> => suspend the compositor (SHIFT+Alt+F12, no shadows, no translucency) or
> use the XRender backend (kcmshell[4] kwincompositing") *Maybe* even
> disabling the blur filter and setting the scale method to anything but
> "accurate" (ie. try smooth) might aid.
> 
> Cheers,
> Thomas
Hello Thomas,
thanks for your reply (which I haven't received through the mailing list for 
some reason but found it on the archive site). Your advice of switching from 
OpenGL to XRender did the trick. Now things are running much smoother than 
before. For the long run I think I would go for a more powerful GPU just as 
Christopher suggested.

Thanks a million!
 Thomas