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[70.24.86.62]) by smtp.gmail.com with ESMTPSA id l16-20020ac84a90000000b003f543cbb698sm3948439qtq.23.2023.05.24.12.24.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 May 2023 12:25:00 -0700 (PDT) Date: Wed, 24 May 2023 15:24:58 -0400 From: Peter Xu To: Avihai Horon Cc: qemu-devel@nongnu.org, Alex Williamson , =?utf-8?Q?C=C3=A9dric?= Le Goater , Eduardo Habkost , Marcel Apfelbaum , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Yanan Wang , Juan Quintela , 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 v3 1/7] migration: Add switchover ack capability Message-ID: References: <20230521151808.24804-1-avihaih@nvidia.com> <20230521151808.24804-2-avihaih@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230521151808.24804-2-avihaih@nvidia.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@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, RCVD_IN_MSPIKE_H2=-0.001, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Sun, May 21, 2023 at 06:18:02PM +0300, 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 "switchover ack" that prevents the > source from stopping the VM and completing the migration until an ACK > is received from the destination that it's OK to do so. > > This can be used by migrated devices in various ways to reduce downtime. > For example, a device can send initial precopy metadata to pre-allocate > resources in the destination and use this capability to make sure that > the pre-allocation is completed before the source VM is stopped, 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 Reviewed-by: Peter Xu -- Peter Xu