Re: [Xen-devel] [PATCH 3/4] usb: Introduce Xen pvUSB backend

[Juergen Gross]

On 03/04/2015 04:27 PM, Greg KH wrote:
> On Wed, Mar 04, 2015 at 02:31:08PM +0100, Juergen Gross wrote:
> > On 03/02/2015 12:39 PM, David Vrabel wrote:
> > > On 26/02/15 13:35, Juergen Gross wrote:
> > > > Introduces the Xen pvUSB backend. With pvUSB it is possible for a Xen
> > > > domU to communicate with a USB device assigned to that domU. The
> > > > communication is all done via the pvUSB backend in a driver domain
> > > > (usually Dom0) which is owner of the physical device.
> > >
> > > Why do we need a kernel usb backend instead of a user-space one using
> > > libusb?
> >
> > Good question. At a first glance libusb seems to offer most/all needed
> > interfaces. The main question is whether performance with libusb will
> > be okay. There will be one additional copy of the I/O data needed if
> > I've read the code in drivers/usb/core/devio.c correctly.
>
> You can drive USB devices at line speed using libusb just fine.  Try it
> out and see please, processors copy data _very_ fast these days.

Okay, thanks for the information.

I'll take this as a hint to try the user space variant. :-)


Juergen

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