From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33236) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zf3ig-0002E8-MK for qemu-devel@nongnu.org; Thu, 24 Sep 2015 06:25:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zf3O4-0004TO-Vj for qemu-devel@nongnu.org; Thu, 24 Sep 2015 06:05:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33521) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zf3O4-0004TD-Nr for qemu-devel@nongnu.org; Thu, 24 Sep 2015 06:04:24 -0400 Date: Thu, 24 Sep 2015 13:04:20 +0300 From: "Michael S. Tsirkin" Message-ID: <20150924125725-mutt-send-email-mst@redhat.com> References: <20150831160655-mutt-send-email-mst@redhat.com> <55ED854A.1080804@huawei.com> <55EFF03A.4000109@huawei.com> <55FC3BE7.5010503@huawei.com> <20150921150953-mutt-send-email-mst@redhat.com> <55FFF8CA.3020008@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55FFF8CA.3020008@siemens.com> Subject: Re: [Qemu-devel] RFC: virtio-peer shared memory based peer communication device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: "virtio-dev@lists.oasis-open.org" , Claudio Fontana , "qemu-devel@nongnu.org" , "virtualization@lists.linux-foundation.org" , "Zhang, Yang Z" , "opnfv-tech-discuss@lists.opnfv.org" On Mon, Sep 21, 2015 at 02:32:10PM +0200, Jan Kiszka wrote: > On 2015-09-21 14:13, Michael S. Tsirkin wrote: > > On Fri, Sep 18, 2015 at 06:29:27PM +0200, Claudio Fontana wrote: > >> Hello, > >> > >> this is a first RFC for virtio-peer 0.1, which is still very much a work in progress: > >> > >> https://github.com/hw-claudio/virtio-peer/wiki > >> > >> It is also available as PDF there, but the text is reproduced here for commenting: > >> > >> Peer shared memory communication device (virtio-peer) > >> > >> General Overview > >> > >> (I recommend looking at the PDF for some clarifying pictures) > >> > >> The Virtio Peer shared memory communication device (virtio-peer) is a > >> virtual device which allows high performance low latency guest to > >> guest communication. It uses a new queue extension feature tentatively > >> called VIRTIO_F_WINDOW which indicates that descriptor tables, > >> available and used rings and Queue Data reside in physical memory > >> ranges called Windows, each identified with an unique identifier > >> called WindowID. > > > > So if I had to summarize the difference from regular virtio, > > I'd say the main one is that this uses window id + offset > > instead of the physical address. > > > > > > My question is - why do it? > > > > All windows are in memory space, are they not? > > > > How about guest using full physical addresses, > > and hypervisor sending the window physical address > > to VM2? > > > > VM2 can uses that to find both window id and offset. > > > > > > This way at least VM1 can use regular virtio without changes. > > What would be the value of having different drivers in VM1 and VM2, > specifically if both run Linux? > > Jan It's common to have a VM act as a switch between others. In this setup, there's value in being able to support existing guests as endpoints, with new drivers only required for the switch. > -- > Siemens AG, Corporate Technology, CT RTC ITP SES-DE > Corporate Competence Center Embedded Linux