Re: [Xen-devel] [PATCH v3 2/6] libxl: do not add a vkb backend to hvm guests

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 30 Jun 2015, Ian Campbell wrote:
> On Mon, 2015-06-29 at 18:59 +0100, Stefano Stabellini wrote:
> > On Thu, 25 Jun 2015, Ian Campbell wrote:
> > > On Tue, 2015-06-16 at 16:39 +0100, Stefano Stabellini wrote:
> > > > On Tue, 16 Jun 2015, Wei Liu wrote:
> > > > > On Wed, Jun 10, 2015 at 11:09:50AM +0100, Stefano Stabellini wrote:
> > > > > > When QEMU restricts its xenstore connection, it cannot provide PV
> > > > > > backends. A separate QEMU instance is required to provide PV 
> > > > > > backends in
> > > > > > userspace, such as qdisk. With two separate instances, it is not
> > > > > > possible to take advantage of vkb for mouse and keyboard, as the 
> > > > > > QEMU
> > > > > > that emulates the graphic card (the device model), would be separate
> > > > > > from the QEMU running the vkb backend (PV QEMU).
> > > > > > 
> > > > > 
> > > > > The question is that how would this affect the non-split setup.
> > > > 
> > > > vkb is useful because emulating usb forces QEMU to wake up more often.
> > > > However there is no way around it.
> > > 
> > > Does pvfb+vkb continue to work due to code somewhere else?
> > 
> > Yes, it continues to work as usual for PV guests.
> > 
> > 
> > > Do we think anyone will actually be using emulated VGA + PV input
> > > devices?
> > 
> > VGA + PV input only works with Linux and is only useful for power
> > efficiency, because if you disable usb emulation in QEMU, then QEMU
> > would be able to wake up less often. Given that usb emulation is still
> > on by default, I don't think that this change will have a big impact.
> 
> My question was whether we thought anyone would be using this
> non-default configuration, not what the impact on the default is.
> 
> You gave a good reason why people might be using this facility, do you
> think anyone is actually using it?
 
I don't know of anybody using it. I don't think we made clear enough how
to use this non-default configuration and its advantages for users to go
out of their ways to use it. 

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