From: "Eric Blake" <eblake(a)redhat.com&gt; To: "For testing and quality assurance of Fedora releases" <test(a)lists.fedoraproject.org&gt; Cc: virt(a)lists.fedoraproject.org Sent: Tuesday, December 6, 2011 6:33:43 PM Subject: Re: [fedora-virt] kvm "tablet" device burning cpu cycles [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. > 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. Meanwhile, sufficiently new qemu provides USB device emulation, which is more efficient than the PCI tablet emulation; although it is not as apparent whether typical guests support that device driver in their default install (one of the reasons we default to the older tablet emulation is that it is likely to have a driver pre-installed on most guest OSs). The idea of swapping the default to a USB pointer should be raised against virt-manager and/or python-virtinst, when installing a new-enough guest OS with new enough qemu support, while continuing to provide the compatible fallback of the tablet for older setups.

-- Eric Blake eblake(a)redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org _______________________________________________ virt mailing list virt(a)lists.fedoraproject.org https://admin.fedoraproject.org/mailman/listinfo/virt

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