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Re: [Xen-users] usb passthrough

To: Pasi Kärkkäinen <pasik@xxxxxx>
Subject: Re: [Xen-users] usb passthrough
From: Chris <tknchris@xxxxxxxxx>
Date: Fri, 26 Feb 2010 19:16:26 -0500
Cc: James Harper <james.harper@xxxxxxxxxxxxxxxx>, "xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>, "Sergio Charpinel Jr." <sergiocharpinel@xxxxxxxxx>
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I wonder why it's limited to 1.1 i would imagine that is a hard coded limit but given a faster system shouldn't the emulation be faster? Who could shed more light on why?

Sent from my iPhone

On Feb 26, 2010, at 5:44 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:

On Fri, Feb 26, 2010 at 05:34:14PM -0500, chris wrote:
I would be curious to see benchmarks comparing usb device passthrough
with vt-d passthrough of a usb controller + device. Would be
interesting to see what differences if any there are. If I get some
time I will try to test this.


See here for benchmark results:
http://www.xen.org/files/xensummit_intel09/PVUSBStatusUpdate.pdf

pvusb performance seems to be pretty close to dom0 native usb performance.

If using the normal qemu-dm usb passthrough it is limited to emulated usb 1.1,
so that'll be slow.

-- Pasi

- chris

On Fri, Feb 26, 2010 at 5:00 PM, James Harper
<james.harper@xxxxxxxxxxxxxxxx> wrote:
Pvusb should work for most things. You might be thinking of the USB frontend in gplpv which only works with a very limited number of storage devices (and
probably not at all since the last update)

James

Sent from my iPhone

On 27/02/2010, at 5:25, "chris" <tknchris@xxxxxxxxx> wrote:

Pasi,

I know, my understanding was that pvusb was simply for exposing usb
mass storage as a block device to the domain. I've never actually used
it but I believe you can do this with a hvm domain without anything
special. If anyone can actually confirm this it would be good to know
:)

As far as his original question, he needs vt-d to passthrough any
physical device to a hvm domain.

- chris

On Fri, Feb 26, 2010 at 10:03 AM, Pasi Kärkkäinen <pasik@xxxxx i> wrote:

On Fri, Feb 26, 2010 at 10:00:34AM -0500, chris wrote:

He said it was a HVM guest. I don't think you can passthrough to a hvm
domain anything except usb storage with pvusb, correct?


pvusb is different from the 'normal' usb=1 / usbdevice = [] stuff..

I'm not totally sure what devices are supported with pvusb and with the
normal usb passthrough.

-- Pasi

On Fri, Feb 26, 2010 at 9:49 AM, Pasi Kärkkäinen <pasik@ik i.fi> wrote:

On Fri, Feb 26, 2010 at 09:49:38AM -0300, Sergio Charpinel Jr. wrote:

Hi,

I want to use a webcam in a HVM guest, but my dom0 doesnt support VT-d
(just VT).


USB passthrough doesn't require VT-d, it's only required for PCI device
passthrough to HVM guests.

I tried passing the parameters usb=1 and usbdevice = [ '..' ] and I could see an usb device in domU. But it does not know which device is.

Which are the possibilites to do that? I prefer to use hvm machines,
but if it is not possible, with PV machines it can work?


With PV guest you could passthrough the whole USB controller (the PCI
device)..

-- Pasi


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