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

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Message-ID: <54F72555.30304@suse.com>
Date:	Wed, 04 Mar 2015 16:31:33 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Greg KH <gregkh@...uxfoundation.org>
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 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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