From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932379AbbCDOlL (ORCPT ); Wed, 4 Mar 2015 09:41:11 -0500 Received: from cantor2.suse.de ([195.135.220.15]:56833 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755514AbbCDOlK (ORCPT ); Wed, 4 Mar 2015 09:41:10 -0500 Message-ID: <54F71983.6070708@suse.com> Date: Wed, 04 Mar 2015 15:41:07 +0100 From: Juergen Gross User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Ian Campbell , David Vrabel CC: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com, linux-usb@vger.kernel.org, gregkh@linuxfoundation.org, cyliu@suse.com Subject: Re: [Xen-devel] [PATCH 3/4] usb: Introduce Xen pvUSB backend References: <1424957717-392-1-git-send-email-jgross@suse.com> <1424957717-392-4-git-send-email-jgross@suse.com> <54F44BD5.1030008@citrix.com> <54F7091C.1050001@suse.com> <54F70E3D.20201@citrix.com> <54F71221.6050800@suse.com> <54F71468.3030207@citrix.com> <1425479350.25940.177.camel@citrix.com> In-Reply-To: <1425479350.25940.177.camel@citrix.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/04/2015 03:29 PM, Ian Campbell wrote: > 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. While I can accept the bus speed reasoning, I doubt qdisk is copying data between user and kernel space under normal circumstances. I think disk I/Os are done using DMA to/from the user buffer directly. > 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. Do you have another feeling about the probability of a need to do usb 3? If it is already on the horizon I wouldn't want to do the user space backend now and the kernel one next year. :-) Juergen