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

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Date:	Wed, 4 Mar 2015 14:29:10 +0000
From:	Ian Campbell <ian.campbell@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<boris.ostrovsky@...cle.com>, <linux-usb@...r.kernel.org>,
	<gregkh@...uxfoundation.org>, <cyliu@...e.com>
Subject: Re: [Xen-devel] [PATCH 3/4] usb: Introduce Xen pvUSB backend

On Wed, 2015-03-04 at 14:19 +0000, David Vrabel wrote:
> On 04/03/15 14:09, Juergen Gross wrote:
> > 
> > The main question whether it is worth to consider this alternative is
> > the performance aspect. Does anyone have an idea which USB devices would
> > typically be used via pvusb? I'd suspect memory sticks and USB disks
> > and perhaps webcams being the most performance relevant ones. Is an
> > additional copy operation of user data acceptable here?
> 
> I have no idea.  We (XenServer) have no use cases at all for USB device
> passthrough.

My gut feeling is that for USB 1 and 2 the bus itself isn't fast enough
that anyone would care. qdisk has acceptable for disks, so it's probably
ok for usb too.

For usb 3 onwards, well, maybe when we care about those we'll decide
that a kernel space driver is needed, but for now it seems like
userspace would be ok.

Ian.

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