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Sun, 28 May 2023 12:42:52 +0000 Received: from DM6PR12MB5549.namprd12.prod.outlook.com ([fe80::c887:8186:c2f0:d7e6]) by DM6PR12MB5549.namprd12.prod.outlook.com ([fe80::c887:8186:c2f0:d7e6%5]) with mapi id 15.20.6433.020; Sun, 28 May 2023 12:42:52 +0000 Message-ID: <32bade47-89f4-ec42-e805-0b7c59a32aa4@nvidia.com> Date: Sun, 28 May 2023 15:42:41 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0 Subject: Re: [PATCH v3 2/7] migration: Implement switchover ack logic Content-Language: en-US To: Peter Xu Cc: qemu-devel@nongnu.org, Alex Williamson , =?UTF-8?Q?C=c3=a9dric_Le_Goater?= , Eduardo Habkost , Marcel Apfelbaum , =?UTF-8?Q?Philippe_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 References: <20230521151808.24804-1-avihaih@nvidia.com> <20230521151808.24804-3-avihaih@nvidia.com> <541dc36f-618e-a2c5-a27f-51db65abecbd@nvidia.com> From: Avihai Horon In-Reply-To: Content-Type: text/plain; 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envelope-from=avihaih@nvidia.com; helo=NAM10-BN7-obe.outbound.protection.outlook.com X-Spam_score_int: -23 X-Spam_score: -2.4 X-Spam_bar: -- X-Spam_report: (-2.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.164, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.093, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-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 25/05/2023 15:44, Peter Xu wrote: > External email: Use caution opening links or attachments > > > On Thu, May 25, 2023 at 12:51:46PM +0300, Avihai Horon wrote: >> However, there is one issue -- we can't send the ACK up here [1], as at that >> point the return path has not been created yet. >> A possible solution is to check for mis->switchover_ack_pending_num == 0 >> when we create the return path and send the ACK there. >> It's not as clean as checking the number of users and ACKing here in the >> same place, but it works. >> >> Do you think it's OK? or do you have another idea? > Good point. It looks fine to me as we create the return path mostly at the > very early stage right after the migration headers. > > Let's just add a comment describing the ordering fact? IMHO it's about > switchover_ack_pending_num won't be used before setup of the return path > due to current wire protocol (we create return path before sending mostly > anything else), so setup it there is fine. Sure, I will also add a comment. Thanks.