Not sure if that is a real bug, but I thought I report it here:

I am running Tumbleweed (latest version, as of now 20190512) on an ASUS PN40
(Celeron N4000@1.1GHz, Gemini lake) for controlling a small telescope (via
INDI).  It is running headless, and I use x11vnc_ssh to connect to it (it runs
a real X session with autologin, icewm as session).

The xserver by default uses the modesetting driver.  With that, when I connect
using xvnc, the CPU load of the X server (X, not xvnc) goes up to some 80-90%
just for displaying the empty desktop, still the display is sluggish close to
being unusable, with sometimes latencies in the second range (this is on a Gbit
cable network).

If instead I use the intel driver (xf86-video-intel) CPU load is below 10%,
screen updates are very quick, without much latency.