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Berrange" , Markus Armbruster Subject: Re: [PATCH V2 13/13] migration: cpr-transfer mode In-Reply-To: References: <87ed4qtpo1.fsf@suse.de> <877caitno5.fsf@suse.de> <8b92a6ee-19f7-4483-9766-6b849cc04017@oracle.com> <97268719-56f3-4d7f-aa21-c04cd0262601@oracle.com> Date: Wed, 09 Oct 2024 19:08:58 -0300 Message-ID: <87plo9rksl.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[99.99%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; TAGGED_RCPT(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_TLS_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[10]; MID_RHS_MATCH_FROM(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[nongnu.org,redhat.com,gmail.com,habkost.net,linaro.org]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid] Received-SPF: pass client-ip=195.135.223.131; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=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 Peter Xu writes: > On Wed, Oct 09, 2024 at 04:18:31PM -0400, Steven Sistare wrote: >> Yes, I am also brainstorming along these lines, looking for more gotcha's, >> but its a big design change. I don't love it so far. >> >> These issues all creep in because of transfer mode. Exec mode did not have this >> problem, as cpr-state is written to an in-memory file. > > I understand. Hopefully we're getting there very soon.. > > I still have concern on having -global used in productions, and meanwhile Agree, but for qtests it should be fine at least. > it might still be challenging for handshake to work as early as cpr stage > even for later, because at least in my mind the handshake still happens in > the main migration channel (where it includes channel establishments etc, > which is not proper during cpr stage). I don't think any form of handshake will be implemented in a month. Maybe it's best we keep that to the side for now. (still, thinking about that virtio-net USO thread, an early handshake could be a good idea, so we could perhaps inform about device incompatibility, etc.) > > I don't really know whether that'll work at last.. > > So in my mind the previous two-steps proposal is so far the only one that > all seem to work, with no unpredictable side effects. > > Said that, maybe we can still think about simpler solutions in the > following days or see others opinions, we don't need to make a decision > today, so maybe there's still better way to go. I thought of putting the caps on the configuration vmstate and using that to set them on the destination, but there's a bit of a chicken and egg problem because we need capabilities set as soon as qemu_start_incoming_migration(). Unless we sent those via the cpr channel. We could split migration_object_init() a bit so we can instantiate some parts of the migration state earlier (I'm not even sure what are the actual dependencies are).