From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60110) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cQsS4-00088K-Jg for qemu-devel@nongnu.org; Tue, 10 Jan 2017 04:10:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cQsS0-0001Hw-OW for qemu-devel@nongnu.org; Tue, 10 Jan 2017 04:10:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53738) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cQsS0-0001Hg-Bq for qemu-devel@nongnu.org; Tue, 10 Jan 2017 04:10:40 -0500 Date: Tue, 10 Jan 2017 10:10:37 +0100 From: Igor Mammedov Message-ID: <20170110101037.75bdb727@nial.brq.redhat.com> In-Reply-To: References: <20170105101246.GC3292@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Live migration + cpu/mem hotplug List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Bob Chen Cc: "Daniel P. Berrange" , qemu-devel@nongnu.org On Tue, 10 Jan 2017 14:28:19 +0800 Bob Chen wrote: > Answer my own question: > > The corresponding cmd-line parameter for memory hot-add by QEMU monitor is, > -object memory-backend-ram,id=mem0,size=1024M -device > pc-dimm,id=dimm0,memdev=mem0 pc-dimm should have additional property -device pc-dimm,id=dimm0,memdev=mem0,hotplugged=on > > 2017-01-05 18:12 GMT+08:00 Daniel P. Berrange : > > > On Thu, Jan 05, 2017 at 04:27:26PM +0800, Bob Chen wrote: > > > Hi, > > > > > > According to the docs, the destination Qemu must have the exactly same > > > parameters as the source one. So if the source has just finished cpu or > > > memory hotplug, what would the dest's parameters be like? > > > > > > Does DIMM device, or logically QOM object, have to be reflected on the > > new > > > command-line parameters? > > > > Yes, if you have hotplugged any type of device since the VM was started, > > the QEMU command line args on the target host must include all the original > > args from the source QEMU, and also any args reflect to reflect the > > hotplugged devices too. > > > > A further complication is that on the target, you must also make sure you > > fully specify *all* device address information (PCI slots, SCSI luns, etc > > etc), because the addresses QEMU assigns to a device after hotplug may > > not be the same as the addresses QEMU assigns to a device whne coldplug. > > > > eg if you boot a guest with 1 NIC + 1 disk, and then hotplug a 2nd NIC > > you might get > > > > 1st NIC == PCI slot 2 > > 1st disk == PCI slot 3 > > 2nd NIC == PCI slot 4 > > > > if however, you started QEMU with 2 NICs and 1 disk straight away QEMU > > might assign addresses in the order > > > > 1st NIC == PCI slot 2 > > 2nd NIC == PCI slot 3 > > 1st disk == PCI slot 4 > > > > this would totally kill a guest OS during live migration as the slots > > for devices its using would change. > > > > So as a general rule when launching QEMU on a target host for migrating, > > you must be explicit about all device addresses and not rely on QEMU to > > auto-assign addresses. This is quite alot of work to get right, but if > > you're using libvirt it'll do pretty much all this automatically for > > you. > > > > Regards, > > Daniel > > -- > > |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ > > :| > > |: http://libvirt.org -o- http://virt-manager.org > > :| > > |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ > > :| > >