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Szmigiero" , =?utf-8?Q?Daniel?= =?utf-8?Q?_P_=2E_Berrang=C3=A9?= , Zhiyi Guo , Juraj Marcin , Peter Xu , Prasad Pandit , Avihai Horon , Kirti Wankhede , =?utf-8?Q?C=C3=A9dric?= Le Goater , Joao Martins , Markus Armbruster , Alex Williamson Subject: Re: [PATCH 12/14] migration: Fix calculation of expected_downtime to take VFIO info In-Reply-To: <20260408165559.157108-13-peterx@redhat.com> References: <20260408165559.157108-1-peterx@redhat.com> <20260408165559.157108-13-peterx@redhat.com> Date: Thu, 09 Apr 2026 19:17:44 -0300 Message-ID: <87y0iv4w3b.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FROM_HAS_DN(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[14]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; MISSING_XM_UA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:dkim,suse.de:mid] X-Rspamd-Action: no action X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: 0D63F6A7D7 Received-SPF: pass client-ip=2a07:de40:b251:101:10:150:64:1; envelope-from=farosas@suse.de; helo=smtp-out1.suse.de 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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, 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: qemu development 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: > QEMU will provide an expected downtime for the whole system during > migration, by remembering the total dirty RAM that we synced the last time, > divides the estimated switchover bandwidth. > > That was flawed when VFIO is taking into account: consider there is a VFIO > GPU device that contains GBs of data to migrate during stop phase. Those > will not be accounted in this math. > > Fix it by updating dirty_bytes_last_sync properly only when we go to the > next iteration, rather than hide this update in the RAM code. Meanwhile, > fetch the total (rather than RAM-only) portion of dirty bytes, so as to > include GPU device states too. > > Update the comment of the field to reflect its new meaning. > > Now after this change, the expected-downtime to be read from query-migrate > should be very accurate even with VFIO devices involved. > > Signed-off-by: Peter Xu > --- > migration/migration-stats.h | 8 +++----- > migration/migration.c | 11 ++++++++--- > migration/ram.c | 1 - > 3 files changed, 11 insertions(+), 9 deletions(-) > > diff --git a/migration/migration-stats.h b/migration/migration-stats.h > index 326ddb0088..1447316802 100644 > --- a/migration/migration-stats.h > +++ b/migration/migration-stats.h > @@ -31,11 +31,9 @@ > */ > typedef struct { > /* > - * Number of bytes that were dirty last time that we synced with > - * the guest memory. We use that to calculate the downtime. As > - * the remaining dirty amounts to what we know that is still dirty > - * since last iteration, not counting what the guest has dirtied > - * since we synchronized bitmaps. > + * Number of bytes that were reported dirty after the lastest typo: latest > + * system-wise synchronization on dirty information. It is used to s/on/of/ ? I can fix these at merge time.