[Pkg-libvirt-maintainers] Bug#672720: Bug#672720: Bug#672720: libvirt-bin: KVM with usb-tablet causes constant CPU load

[Guido Günther]

On Mon, May 14, 2012 at 10:59:06PM +0300, Kari Pahula wrote:
> Sorry, but could you please clarify these two statements?
> 
> On Mon, May 14, 2012 at 09:24:56PM +0200, Guido Günther wrote:
> > Yes the usb table hogging the cpu is a known issue:
> > 
> > 	http://lists.gnu.org/archive/html/qemu-devel/2010-04/msg00149.html
> > 
> > however the cpu load should drop to zero even when you have the usb
> > tablet enabled.
> 
> > > I'll leave it to you to decide what to do with this information.  Can
> > > anyone reproduce this?
> > 
> > Yes. Saving cpu cycles without the tables is reproducable here.
> 
> Does usb-tablet cause extra cpu load or not?

Yes, it does cause extra cpu load.

> According to powertop, with usb-tablet, I didn't see wakeups/second go
> under 800.  Without, the system easily reached 150.
> 
> > Did you create the vm using virt-manager? It's adding the tablet by
> > default since we can't easily distinguish between systems that need it
> > and those that don't.
> 
> With virt-install.

O.k. both use the same code to detect the vm parameters.

> 
> Is this a good default?  I'd expect tablets to be quite rare.

It's used to avoid grabs so you can simply move the mouse pointer in and
out of the VMs window so it has it's uses but I'm not sure if it's worth
the trouble either.
Cheers,
 -- Guido