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[188.85.120.92]) by smtp.gmail.com with ESMTPSA id b10-20020adfee8a000000b002f013fb708fsm16789975wro.4.2023.05.10.01.24.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 May 2023 01:24:13 -0700 (PDT) From: Juan Quintela To: Avihai Horon Cc: , Alex Williamson , =?utf-8?Q?C=C3=A9dric?= Le Goater , Peter Xu , Leonardo Bras , Eric Blake , Markus Armbruster , Thomas Huth , Laurent Vivier , Paolo Bonzini , Yishai Hadas , Jason Gunthorpe , Maor Gottlieb , Kirti Wankhede , Tarun Gupta , Joao Martins Subject: Re: [PATCH 1/8] migration: Add precopy initial data capability In-Reply-To: <20230501140141.11743-2-avihaih@nvidia.com> (Avihai Horon's message of "Mon, 1 May 2023 17:01:34 +0300") References: <20230501140141.11743-1-avihaih@nvidia.com> <20230501140141.11743-2-avihaih@nvidia.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) Date: Wed, 10 May 2023 10:24:12 +0200 Message-ID: <87o7msa91v.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=170.10.129.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Avihai Horon wrote: > Migration downtime estimation is calculated based on bandwidth and > remaining migration data. This assumes that loading of migration data in > the destination takes a negligible amount of time and that downtime > depends only on network speed. > > While this may be true for RAM, it's not necessarily true for other > migration users. For example, loading the data of a VFIO device in the > destination might require from the device to allocate resources, prepare > internal data structures and so on. These operations can take a > significant amount of time which can increase migration downtime. > > This patch adds a new capability "precopy initial data" that allows the > source to send initial precopy data and the destination to ACK that this > data has been loaded. Migration will not attempt to stop the source VM > and complete the migration until this ACK is received. > > This will allow migration users to send initial precopy data which can > be used to reduce downtime (e.g., by pre-allocating resources), while > making sure that the source will stop the VM and complete the migration > only after this initial precopy data is sent and loaded in the > destination so it will have full effect. > > This new capability relies on the return path capability to communicate > from the destination back to the source. > > The actual implementation of the capability will be added in the > following patches. > > Signed-off-by: Avihai Horon Capability definition is correct. I am not given the review-by until the rest of the series is discussed, but nothing else to do here.