From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v5 1/6] libxl: do not add a vkb backend to hvm guests Date: Fri, 24 Jul 2015 12:10:24 +0100 Message-ID: <1437736224.24746.71.camel@citrix.com> References: <1437672464-29909-1-git-send-email-stefano.stabellini@eu.citrix.com> <9AAE0902D5BC7E449B7C8E4E778ABCD02F4D3393@AMSPEX01CL02.citrite.net> <9AAE0902D5BC7E449B7C8E4E778ABCD02F4D37D1@AMSPEX01CL02.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Stefano Stabellini , Paul Durrant Cc: Wei Liu , "xen-devel@lists.xensource.com" , Stefano Stabellini , Ian Jackson List-Id: xen-devel@lists.xenproject.org On Fri, 2015-07-24 at 11:56 +0100, Stefano Stabellini wrote: > On Fri, 24 Jul 2015, Paul Durrant wrote: > > > -----Original Message----- > > > From: Stefano Stabellini [mailto:stefano.stabellini@eu.citrix.com > > > ] > > > Sent: 24 July 2015 11:21 > > > To: Paul Durrant > > > Cc: Stefano Stabellini; xen-devel@lists.xensource.com; Wei Liu; > > > Ian Jackson; > > > Ian Campbell > > > Subject: RE: [Xen-devel] [PATCH v5 1/6] libxl: do not add a vkb > > > backend to > > > hvm guests > > > > > > On Fri, 24 Jul 2015, Paul Durrant wrote: > > > > > -----Original Message----- > > > > > From: xen-devel-bounces@lists.xen.org [mailto:xen-devel- > > > > > bounces@lists.xen.org] On Behalf Of Stefano Stabellini > > > > > Sent: 23 July 2015 18:28 > > > > > To: xen-devel@lists.xensource.com > > > > > Cc: Wei Liu; Ian Jackson; Ian Campbell; Stefano Stabellini > > > > > Subject: [Xen-devel] [PATCH v5 1/6] libxl: do not add a vkb > > > > > backend to > > > hvm > > > > > guests > > > > > > > > > > When QEMU restricts its xenstore connection, it cannot > > > > > provide PV > > > > > backends. A separate QEMU instance is required to provide PV > > > > > backends > > > in > > > > > userspace, such as qdisk. With two separate instances, it is > > > > > not > > > > > possible to take advantage of vkb for mouse and keyboard, as > > > > > the QEMU > > > > > that emulates the graphic card (the device model), would be > > > > > separate > > > > > from the QEMU running the vkb backend (PV QEMU). > > > > > > > > > > Removing this functionality is acceptable, because is only > > > > > useful for > > > > > power saving when usb emulation is off, letting QEMU sleep > > > > > for longer > > > > > periods of time. However usb emulation is on by default, and > > > > > how to > > > > > take advantage of this configuration has never been > > > > > documented. > > > > > > > > > > > > > I don't think I agree. Turning off USB emulation for HVM guests > > > > (particularly > > > Windows) has been shown to be highly advantageous in performance > > > and > > > scalability terms, and we have a prototype HID driver (not yet > > > part of the > > > XenProject driver set, but hopefully soon will be) which uses > > > vkb. > > > > > > I would appreciate if this kind of comments were made at v1 or > > > v2, not > > > v5 of a series :-) > > > > > > > Yes, I realise that, but I've been busy... sorry. > > > > > > > > I know that turning USB emulation off is a big win, but nobody is > > > really > > > doing it. The reason is that we didn't properly documented how to > > > do it. > > > > It's documented for XenServer and we have toolstack support to do > > it. > > You could still use it if you call libxl_device_vkb_add explicitely and > you avoid creating any of depriv QEMU users (xen-qemudepriv-domid* and > xen-qemudepriv-shared). There really ought to be a way at the libxl level (but not necessarily in xl) to disable the depriv without having to arrange things "just so" such that it doesn't occur... Ian.