[fedora-virt] kvm "tablet" device burning cpu cycles

[Dennis Jacobfeuerborn]

On 12/07/2011 10:20 AM, Daniel P. Berrange wrote:
> On Tue, Dec 06, 2011 at 04:33:43PM -0700, Eric Blake wrote:
>> [redirecting to the fedora virt list]
>>
>> On 12/06/2011 03:36 PM, Dennis Jacobfeuerborn wrote:
>>> Hi,
>>> I noticed that when you install a virtual system with virt-manager it
>>> always installs a tablet device by default.
>>> The problem is that this device consumes 10% of cpu resources of the host
>>> according to "top" which should probably be considered a bug.
>>
>> The poor behavior of a tablet device should be raised against the qemu
>> team, to see if it can be made more efficient.
>
> This is a long standing problem, but it shouldn't be taking anywhree
> near 10% of CPU.
>
> If using SPICE with the SPICE guest agent installed there is a parvirt
> mouse available, avoiding the need for the USB tablet.

I did some more testing today and also installed a Fedora 16 VM. Here I
don't see the big overhead and an idle guest is also idle on the host so it 
seems this is an issue with the driver on the guest side. While I tried
SPICE I didn't play with the guest agent yet. When using SPICE I switch the 
display device from VNC to SPICE and let virt-manager add an additional 
channel device (it asks me if it should do so). Is it sufficient to install 
spice-vdagent in the guest to make use of the client mouse mode?

>
>>
>>> What is worse is that removing the tablet also means no mouse pointer
>>> showing up in a centos 6 guest which means you are pretty much forced to
>>> use the tablet device.
>
> That shouldn't be the case. If you boot the guest with no USB tablet
> present, X should auto-detect the PS2 mouse and use that. You would
> only have trouble if either hot-unpluging the USB tablet, or if you
> have hardcoded its use in /etc/X11/xorg.conf

I experimented a bit and I only see this:
1) when I use "qxl" as video model
2) when I keep the graphical console open in virt-manager after booting

When I close the window and reopen it again the mouse pointer is there and
when I use "cirrus" as model the problem doesn't happen at all.

Regards,
    Dennis