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[184.145.4.219]) by smtp.gmail.com with ESMTPSA id g140sm3662918qke.32.2021.05.07.07.57.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 07 May 2021 07:57:16 -0700 (PDT) Date: Fri, 7 May 2021 10:57:15 -0400 From: Peter Xu To: Kunkun Jiang Subject: Re: [question] The source cannot recover, if the destination fails in the last round of live migration Message-ID: References: <7d87a3b7-86c9-9248-59dc-e1612a00e7c3@huawei.com> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juan Quintela , David Edmondson , "open list:All patches CC here" , "Dr. David Alan Gilbert" , Zenghui Yu , wanghaibin.wang@huawei.com, Keqian Zhu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, May 07, 2021 at 05:46:44PM +0800, Kunkun Jiang wrote: > Hi Dave, > > On 2021/5/6 21:05, Dr. David Alan Gilbert wrote: > > * Kunkun Jiang (jiangkunkun@huawei.com) wrote: > > > Hi all, > > Hi, > > > > > Recently I am learning about the part of live migration. > > > I have a question about the last round. > > > > > > When the pending_size is less than the threshold, it will enter > > > the last round and call migration_completion(). It will stop the > > > source and sent the remaining dirty pages and devices' status > > > information to the destination. The destination will load these > > > information and start the VM. > > > > > > If there is an error at the destination at this time, it will exit > > > directly, and the source will not be able to detect the error > > > and recover. Because the source will not call > > > migration_detect_error(). > > > > > > Is my understanding correct? > > > Should the source wait the result of the last round of destination ? > > Try setting the 'return-path' migration capability on both the source > > and destination; I think it's that option will cause the destination to > > send an OK/error at the end and the source to wait for it. > Thank you for your reply! > The 'return-path' migration capability solved my question. 😁 > > But why not set it as the default? In my opinion, it is a basic ability > of live migration. We need it to judge whether the last round of the > destination is successful in the way of 'precopy'. I think it should be enabled as long as both sides support it; though may not be suitable as default (at least in QEMU) so as to consider old binaries. Thanks, -- Peter Xu