Cursor redraws very slowly in Dom0

[Geoff Gibbs <g.gibbs42@xxxxxxxxx>]

Hallo,

I have an odd artefact involving the cursor redrawing very slowly
when it changes between cursors, say from the "I" cursor to the
"drag and stretch" cursor. It can take several seconds to complete
the redraw and seems to redraw by random scan lines. This also
similarly affects a certain type of pop-up. Normal X programs
open without delay and can be dragged around without significant
delay.

My graphics card is an integrated Intel i915.

This artefact only occurs when I boot using the Xen hypervisor.
Booting on bare metal is ok, but booting as Dom0 with Xen produces this
slow redraw. I am currently on Devuan Chimaera (= Debian Bullseye),
kernel 5.10.0-10-amd64 and Xen 4.14.4-pre although my failing memory
tells me that I had this effect earlier!
xorg-server 2:1.20.11-1+deb11u1 (https://www.debian.org/support)

Devuan is booting in paravirtual mode (PV), as Dom0.
When I boot a PV DomU, and connect a vncviewer on Dom0
to the qemu vncserver to access the X session on the DomU,
the X windows in the VNC display do not have this artefact.
If, however, I open an ssh connection to DomU and run a vncserver
on DomU and connect to it from Dom0 with a vncviewer,
then the artefact still occurs but less slowly.
My recent tests were with Void Linux as DomU.

All the best

Geoff