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

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Date:	Wed, 4 Mar 2015 07:27:22 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Juergen Gross <jgross@...e.com>
Cc:	David Vrabel <david.vrabel@...rix.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	linux-usb@...r.kernel.org, cyliu@...e.com
Subject: Re: [Xen-devel] [PATCH 3/4] usb: Introduce Xen pvUSB backend

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.

thanks,

greg k-h
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