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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7a9a7969043sm237868685a.44.2024.09.09.10.59.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Sep 2024 10:59:55 -0700 (PDT) Date: Mon, 9 Sep 2024 13:59:53 -0400 From: Peter Xu To: Avihai Horon Cc: "Maciej S. Szmigiero" , Fabiano Rosas , Alex Williamson , =?utf-8?Q?C=C3=A9dric?= Le Goater , Eric Blake , Markus Armbruster , Daniel P =?utf-8?B?LiBCZXJyYW5nw6k=?= , Joao Martins , qemu-devel@nongnu.org Subject: Re: [PATCH v2 06/17] migration: Add save_live_complete_precopy_{begin,end} handlers Message-ID: References: <9f9f0408-866d-4dc8-8c8e-80c3cfdd190a@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <9f9f0408-866d-4dc8-8c8e-80c3cfdd190a@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: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.141, 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_H3=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: 2.1.29 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 Thu, Sep 05, 2024 at 04:45:48PM +0300, Avihai Horon wrote: > > On 27/08/2024 20:54, Maciej S. Szmigiero wrote: > > External email: Use caution opening links or attachments > > > > > > From: "Maciej S. Szmigiero" > > > > These SaveVMHandlers help device provide its own asynchronous > > transmission of the remaining data at the end of a precopy phase. > > > > In this use case the save_live_complete_precopy_begin handler might > > be used to mark the stream boundary before proceeding with asynchronous > > transmission of the remaining data while the > > save_live_complete_precopy_end handler might be used to mark the > > stream boundary after performing the asynchronous transmission. > > > > Signed-off-by: Maciej S. Szmigiero > > --- > > include/migration/register.h | 36 ++++++++++++++++++++++++++++++++++++ > > migration/savevm.c | 35 +++++++++++++++++++++++++++++++++++ > > 2 files changed, 71 insertions(+) > > > > diff --git a/include/migration/register.h b/include/migration/register.h > > index f60e797894e5..9de123252edf 100644 > > --- a/include/migration/register.h > > +++ b/include/migration/register.h > > @@ -103,6 +103,42 @@ typedef struct SaveVMHandlers { > > */ > > int (*save_live_complete_precopy)(QEMUFile *f, void *opaque); > > > > + /** > > + * @save_live_complete_precopy_begin > > + * > > + * Called at the end of a precopy phase, before all > > + * @save_live_complete_precopy handlers and before launching > > + * all @save_live_complete_precopy_thread threads. > > + * The handler might, for example, mark the stream boundary before > > + * proceeding with asynchronous transmission of the remaining data via > > + * @save_live_complete_precopy_thread. > > + * When postcopy is enabled, devices that support postcopy will skip this step. > > + * > > + * @f: QEMUFile where the handler can synchronously send data before returning > > + * @idstr: this device section idstr > > + * @instance_id: this device section instance_id > > + * @opaque: data pointer passed to register_savevm_live() > > + * > > + * Returns zero to indicate success and negative for error > > + */ > > + int (*save_live_complete_precopy_begin)(QEMUFile *f, > > + char *idstr, uint32_t instance_id, > > + void *opaque); > > + /** > > + * @save_live_complete_precopy_end > > + * > > + * Called at the end of a precopy phase, after @save_live_complete_precopy > > + * handlers and after all @save_live_complete_precopy_thread threads have > > + * finished. When postcopy is enabled, devices that support postcopy will > > + * skip this step. > > + * > > + * @f: QEMUFile where the handler can synchronously send data before returning > > + * @opaque: data pointer passed to register_savevm_live() > > + * > > + * Returns zero to indicate success and negative for error > > + */ > > + int (*save_live_complete_precopy_end)(QEMUFile *f, void *opaque); > > Is this handler necessary now that migration core is responsible for the > threads and joins them? I don't see VFIO implementing it later on. Right, I spot the same thing. This series added three hooks: begin, end, precopy_thread. What I think is it only needs one, which is precopy_async. My vague memory was that was what we used to discuss too, so that when migration precopy flushes the final round of iterable data, it does: (1) loop over all complete_precopy_async() and enqueue the tasks if existed into the migration worker pool. Then, (2) loop over all complete_precopy() like before. Optionally, we can enforce one vmstate handler only provides either complete_precopy_async() or complete_precopy(). In this case VFIO can update the two hooks during setup() by detecting multifd && !mapped_ram && nocomp. -- Peter Xu