From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59950) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ze0H1-0003BA-KI for qemu-devel@nongnu.org; Mon, 21 Sep 2015 08:32:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Ze0Gw-0006Rb-Kz for qemu-devel@nongnu.org; Mon, 21 Sep 2015 08:32:47 -0400 Received: from thoth.sbs.de ([192.35.17.2]:49011) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ze0Gw-0006RP-Bi for qemu-devel@nongnu.org; Mon, 21 Sep 2015 08:32:42 -0400 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> From: Jan Kiszka Message-ID: <55FFF8CA.3020008@siemens.com> Date: Mon, 21 Sep 2015 14:32:10 +0200 MIME-Version: 1.0 In-Reply-To: <20150921150953-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit 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: "Michael S. Tsirkin" , Claudio Fontana Cc: "Zhang, Yang Z" , "virtio-dev@lists.oasis-open.org" , "opnfv-tech-discuss@lists.opnfv.org" , "qemu-devel@nongnu.org" , "virtualization@lists.linux-foundation.org" 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 -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux