From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=41534 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OBWKK-000863-U6 for qemu-devel@nongnu.org; Mon, 10 May 2010 12:59:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OBWKF-0001YE-ED for qemu-devel@nongnu.org; Mon, 10 May 2010 12:59:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:14374) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OBWKF-0001Y9-75 for qemu-devel@nongnu.org; Mon, 10 May 2010 12:59:27 -0400 Message-ID: <4BE83B69.4040904@redhat.com> Date: Mon, 10 May 2010 19:59:21 +0300 From: Avi Kivity MIME-Version: 1.0 References: <1271872408-22842-1-git-send-email-cam@cs.ualberta.ca> <1271872408-22842-2-git-send-email-cam@cs.ualberta.ca> <1271872408-22842-3-git-send-email-cam@cs.ualberta.ca> <1271872408-22842-4-git-send-email-cam@cs.ualberta.ca> <1271872408-22842-5-git-send-email-cam@cs.ualberta.ca> <4BE7F517.5010707@redhat.com> <4BE82623.4000905@redhat.com> <4BE82877.1040408@codemonkey.ws> In-Reply-To: <4BE82877.1040408@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [PATCH v5 4/5] Inter-VM shared memory PCI device List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Cam Macdonell , qemu-devel@nongnu.org, kvm@vger.kernel.org On 05/10/2010 06:38 PM, Anthony Liguori wrote: > >>> Otherwise, if the BAR is allocated during initialization, I would have >>> to use MAP_FIXED to mmap the memory. This is what I did before the >>> qemu_ram_mmap() function was added. >> >> What would happen to any data written to the BAR before the the >> handshake completed? I think it would disappear. > > You don't have to do MAP_FIXED. You can allocate a ram area and map > that in when disconnected. When you connect, you create another ram > area and memcpy() the previous ram area to the new one. You then map > the second ram area in. But it's a shared memory area. Other peers could have connected and written some data in. The memcpy() would destroy their data. > > From the guest's perspective, it's totally transparent. For the > backend, I'd suggest having an explicit "initialized" ack or something > so that it knows that the data is now mapped to the guest. From the peers' perspective, it's non-transparent :( Also it doubles the transient memory requirement. > > If you're doing just a ring queue in shared memory, it should allow > disconnect/reconnect during live migration asynchronously to the > actual qemu live migration. > Live migration of guests using shared memory is interesting. You'd need to freeze all peers on one node, disconnect, reconnect, and restart them on the other node. -- error compiling committee.c: too many arguments to function