I'm playing around with kf5 and would like to use sddm. I build all packages (similar to lfs) and while sddm appears to be functioning, there are several issues which are show-stoppers in my judgement. I'll focus on one here: once sddm-greeter has started and is simply idling, waiting for user login (the password entry field has focus), sddm-greeter shows an alarmingly high cpu usage. In particular, by theme, we have:
breeze .. 5-10 % cpu
maui ..... 60-80 % cpu
circles ... 20-27 % cpu

Observations:

• once logged in, cpu usage drops to 0-0.7 % cpu
• in the maui theme, if I do not set focus: true in the listview element, then sdd-greeter will start up
  without the password field having focus, and we get 0 % cpu; but as soon as I click on the password field, cpu usage goes to 60-80 %
• in the maui theme, if I remove the clock from Main.qml, we get 23-28 % cpu

Systems:
All are i686-pc-linux-gnu, with qt-opensource5.5.3.2, gcc-4.9.2, glibc-2.20, linux-3.17.4, and systemd-217
All exhibit the same behavior, same cpu usage
One system uses llvmpipe, one uses i915/opengl 2.1, and another a radeon x1400/opengl 2.1

It looks kinda like something is triggering qt/qtquick to do screen updates frequently and unnecessarily. Has anyone else seen this kind of behavior ?