Constant high cpu usage in xenial under qxl/spice

[Daniel D.]

Both VMs that I upgraded to Xenial experience constant high cpu usage, and top reports compiz is by far the high user of cpu.

The high cpu usage is more apparent from outside the machine, were host reports guests are using close (or over at times) to 200% cpu, than in the guests which are reporting 60-100% cpu (multicore VM) for compiz, constantly.

The VMs are using the QXL video driver and are using a spice channel for virt-manager / virt-viewer.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Daniel D. (cshoredaniel-deactivatedaccount)]

It turns out this is because of a kernel bug (see https://<email address hidden>/msg1152720.html).

A workaround to to add qxl.modeset=0 in /etc/default/grub for the kernel commandline. After update-grub and reboot CPU usage is back to being reasonable.

This also fixes the problem mentioned in the above email thread where even when using virt-viewer QXL multihead fails to report more than one availble display.

With qxl.modeset=0 virt-viewer correctly allows you to turn on up to four virtual displays.