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

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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.

> 
> > 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

> 
> Meanwhile, sufficiently new qemu provides USB device emulation, which is
> more efficient than the PCI tablet emulation;

Actually the tablet is a USB device, not a PCI device.


Daniel
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