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[70.24.86.62]) by smtp.gmail.com with ESMTPSA id i10-20020a37c20a000000b0075902dffce7sm3493110qkm.100.2023.05.24.12.32.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 May 2023 12:32:10 -0700 (PDT) Date: Wed, 24 May 2023 15:32:08 -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 2/7] migration: Implement switchover ack logic Message-ID: References: <20230521151808.24804-1-avihaih@nvidia.com> <20230521151808.24804-3-avihaih@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230521151808.24804-3-avihaih@nvidia.com> Received-SPF: pass client-ip=170.10.133.124; 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 06:18:03PM +0300, Avihai Horon wrote: > Implement switchover ack logic. This 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. > > To achieve this, a new SaveVMHandlers handler switchover_ack_needed() > and a new return path message MIG_RP_MSG_SWITCHOVER_ACK are added. > > The switchover_ack_needed() handler is called during migration setup > both in the source and the destination to check if switchover ack is > used by the migrated device. > > When switchover is approved by all migrated devices in the destination > that support this capability, the MIG_RP_MSG_INITIAL_DATA_LOADED_ACK s/MIG_RP_MSG_INITIAL_DATA_LOADED_ACK/MIG_RP_MSG_SWITCHOVER_ACK/ > return path message is sent to the source to notify it that it's OK to > do switchover. > > Signed-off-by: Avihai Horon > --- > include/migration/register.h | 3 ++ > migration/migration.h | 16 +++++++++++ > migration/savevm.h | 2 ++ > migration/migration.c | 42 +++++++++++++++++++++++++-- > migration/savevm.c | 56 ++++++++++++++++++++++++++++++++++++ > migration/trace-events | 4 +++ > 6 files changed, 121 insertions(+), 2 deletions(-) > > diff --git a/include/migration/register.h b/include/migration/register.h > index a8dfd8fefd..cda36d377b 100644 > --- a/include/migration/register.h > +++ b/include/migration/register.h > @@ -71,6 +71,9 @@ typedef struct SaveVMHandlers { > int (*load_cleanup)(void *opaque); > /* Called when postcopy migration wants to resume from failure */ > int (*resume_prepare)(MigrationState *s, void *opaque); > + > + /* Checks if switchover ack should be used. Called both in src and dest */ > + bool (*switchover_ack_needed)(void *opaque); Sorry if I'm going to suggest something that overwrites what I suggested.. :( Luckily, not so much. When I read the new series I just noticed maybe it's still better to only use this on dst, and always do the ACK. The problem is based on your patch 1 description, the RP ACK message will be sent if the switchover-ack cap is set, but actually it's conditionally in the current impl just to handle num==0 case, so either the impl needs change or the desc needs change. It turns out it'll be even cleaner to always send it. If so.. > } SaveVMHandlers; > > int register_savevm_live(const char *idstr, > diff --git a/migration/migration.h b/migration/migration.h > index 48a46123a0..e209860cce 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -209,6 +209,13 @@ struct MigrationIncomingState { > * contains valid information. > */ > QemuMutex page_request_mutex; > + > + /* > + * Number of devices that have yet to approve switchover. When this reaches > + * zero an ACK that it's OK to do switchover is sent to the source. No lock > + * is needed as this field is updated serially. > + */ > + unsigned int switchover_ack_pending_num; > }; > > MigrationIncomingState *migration_incoming_get_current(void); > @@ -437,6 +444,14 @@ struct MigrationState { > > /* QEMU_VM_VMDESCRIPTION content filled for all non-iterable devices. */ > JSONWriter *vmdesc; > + > + /* Number of devices that use switchover ack capability */ > + unsigned int switchover_ack_user_num; ... we save this field, then... > + /* > + * Indicates whether an ACK from the destination that it's OK to do > + * switchover has been received. > + */ > + bool switchover_acked; > }; > > void migrate_set_state(int *state, int old_state, int new_state); > @@ -477,6 +492,7 @@ int migrate_send_rp_message_req_pages(MigrationIncomingState *mis, > void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis, > char *block_name); > void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value); > +int migrate_send_rp_switchover_ack(MigrationIncomingState *mis); > > void dirty_bitmap_mig_before_vm_start(void); > void dirty_bitmap_mig_cancel_outgoing(void); > diff --git a/migration/savevm.h b/migration/savevm.h > index fb636735f0..5c3e1a026b 100644 > --- a/migration/savevm.h > +++ b/migration/savevm.h > @@ -32,6 +32,7 @@ > bool qemu_savevm_state_blocked(Error **errp); > void qemu_savevm_non_migratable_list(strList **reasons); > void qemu_savevm_state_setup(QEMUFile *f); > +void qemu_savevm_state_switchover_ack_needed(MigrationState *ms); > bool qemu_savevm_state_guest_unplug_pending(void); > int qemu_savevm_state_resume_prepare(MigrationState *s); > void qemu_savevm_state_header(QEMUFile *f); > @@ -65,6 +66,7 @@ int qemu_loadvm_state(QEMUFile *f); > void qemu_loadvm_state_cleanup(void); > int qemu_loadvm_state_main(QEMUFile *f, MigrationIncomingState *mis); > int qemu_load_device_state(QEMUFile *f); > +int qemu_loadvm_approve_switchover(void); > int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f, > bool in_postcopy, bool inactivate_disks); > > diff --git a/migration/migration.c b/migration/migration.c > index 5de7f734b9..87423ec30c 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -78,6 +78,7 @@ enum mig_rp_message_type { > MIG_RP_MSG_REQ_PAGES, /* data (start: be64, len: be32) */ > MIG_RP_MSG_RECV_BITMAP, /* send recved_bitmap back to source */ > MIG_RP_MSG_RESUME_ACK, /* tell source that we are ready to resume */ > + MIG_RP_MSG_SWITCHOVER_ACK, /* Tell source it's OK to do switchover */ > > MIG_RP_MSG_MAX > }; > @@ -760,6 +761,11 @@ bool migration_has_all_channels(void) > return true; > } > > +int migrate_send_rp_switchover_ack(MigrationIncomingState *mis) > +{ > + return migrate_send_rp_message(mis, MIG_RP_MSG_SWITCHOVER_ACK, 0, NULL); > +} > + > /* > * Send a 'SHUT' message on the return channel with the given value > * to indicate that we've finished with the RP. Non-0 value indicates > @@ -1405,6 +1411,8 @@ void migrate_init(MigrationState *s) > s->vm_was_running = false; > s->iteration_initial_bytes = 0; > s->threshold_size = 0; > + s->switchover_ack_user_num = 0; > + s->switchover_acked = false; > } > > int migrate_add_blocker_internal(Error *reason, Error **errp) > @@ -1721,6 +1729,7 @@ static struct rp_cmd_args { > [MIG_RP_MSG_REQ_PAGES_ID] = { .len = -1, .name = "REQ_PAGES_ID" }, > [MIG_RP_MSG_RECV_BITMAP] = { .len = -1, .name = "RECV_BITMAP" }, > [MIG_RP_MSG_RESUME_ACK] = { .len = 4, .name = "RESUME_ACK" }, > + [MIG_RP_MSG_SWITCHOVER_ACK] = { .len = 0, .name = "SWITCHOVER_ACK" }, > [MIG_RP_MSG_MAX] = { .len = -1, .name = "MAX" }, > }; > > @@ -1959,6 +1968,11 @@ retry: > } > break; > > + case MIG_RP_MSG_SWITCHOVER_ACK: > + ms->switchover_acked = true; > + trace_source_return_path_thread_switchover_acked(); > + break; > + > default: > break; > } > @@ -2700,6 +2714,25 @@ static void migration_update_counters(MigrationState *s, > bandwidth, s->threshold_size); > } > > +static bool migration_can_switchover(MigrationState *s) > +{ > + if (!migrate_switchover_ack()) { > + return true; > + } > + > + /* Switchover ack was enabled but no device uses it */ > + if (!s->switchover_ack_user_num) { > + return true; > + } ... we drop this, then... > + > + /* No reason to wait for switchover ACK if VM is stopped */ > + if (!runstate_is_running()) { > + return true; > + } > + > + return s->switchover_acked; > +} > + > /* Migration thread iteration status */ > typedef enum { > MIG_ITERATE_RESUME, /* Resume current iteration */ > @@ -2715,6 +2748,7 @@ static MigIterateState migration_iteration_run(MigrationState *s) > { > uint64_t must_precopy, can_postcopy; > bool in_postcopy = s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE; > + bool can_switchover = migration_can_switchover(s); > > qemu_savevm_state_pending_estimate(&must_precopy, &can_postcopy); > uint64_t pending_size = must_precopy + can_postcopy; > @@ -2727,14 +2761,14 @@ static MigIterateState migration_iteration_run(MigrationState *s) > trace_migrate_pending_exact(pending_size, must_precopy, can_postcopy); > } > > - if (!pending_size || pending_size < s->threshold_size) { > + if ((!pending_size || pending_size < s->threshold_size) && can_switchover) { > trace_migration_thread_low_pending(pending_size); > migration_completion(s); > return MIG_ITERATE_BREAK; > } > > /* Still a significant amount to transfer */ > - if (!in_postcopy && must_precopy <= s->threshold_size && > + if (!in_postcopy && must_precopy <= s->threshold_size && can_switchover && > qatomic_read(&s->start_postcopy)) { > if (postcopy_start(s)) { > error_report("%s: postcopy failed to start", __func__); > @@ -2959,6 +2993,10 @@ static void *migration_thread(void *opaque) > > qemu_savevm_state_setup(s->to_dst_file); > > + if (migrate_switchover_ack()) { > + qemu_savevm_state_switchover_ack_needed(s); > + } ... we also drop this, then... > + > qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP, > MIGRATION_STATUS_ACTIVE); > > diff --git a/migration/savevm.c b/migration/savevm.c > index 03795ce8dc..9482b1ff27 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -1233,6 +1233,23 @@ bool qemu_savevm_state_guest_unplug_pending(void) > return false; > } > > +void qemu_savevm_state_switchover_ack_needed(MigrationState *ms) > +{ > + SaveStateEntry *se; > + > + QTAILQ_FOREACH(se, &savevm_state.handlers, entry) { > + if (!se->ops || !se->ops->switchover_ack_needed) { > + continue; > + } > + > + if (se->ops->switchover_ack_needed(se->opaque)) { > + ms->switchover_ack_user_num++; > + } > + } > + > + trace_savevm_state_switchover_ack_needed(ms->switchover_ack_user_num); > +} ... we also drop this, then... > + > void qemu_savevm_state_setup(QEMUFile *f) > { > MigrationState *ms = migrate_get_current(); > @@ -2586,6 +2603,23 @@ static int qemu_loadvm_state_header(QEMUFile *f) > return 0; > } > > +static void qemu_loadvm_state_switchover_ack_needed(MigrationIncomingState *mis) > +{ > + SaveStateEntry *se; > + > + QTAILQ_FOREACH(se, &savevm_state.handlers, entry) { > + if (!se->ops || !se->ops->switchover_ack_needed) { > + continue; > + } > + > + if (se->ops->switchover_ack_needed(se->opaque)) { > + mis->switchover_ack_pending_num++; > + } > + } > + > + trace_loadvm_state_switchover_ack_needed(mis->switchover_ack_pending_num); > +} > + > static int qemu_loadvm_state_setup(QEMUFile *f) > { > SaveStateEntry *se; > @@ -2789,6 +2823,10 @@ int qemu_loadvm_state(QEMUFile *f) > return -EINVAL; > } > > + if (migrate_switchover_ack()) { > + qemu_loadvm_state_switchover_ack_needed(mis); ... here, we send ACK msg if num==0. So we (1) make the wire protocol clearer (ACK must be there if cap set), then (2) drop a bunch of code too. Actually we also make the code clearer too on src. What do you think? Other than that this looks very good to me. > + } > + > cpu_synchronize_all_pre_loadvm(); > > ret = qemu_loadvm_state_main(f, mis); > @@ -2862,6 +2900,24 @@ int qemu_load_device_state(QEMUFile *f) > return 0; > } > > +int qemu_loadvm_approve_switchover(void) > +{ > + MigrationIncomingState *mis = migration_incoming_get_current(); > + > + if (!mis->switchover_ack_pending_num) { > + return -EINVAL; > + } > + > + mis->switchover_ack_pending_num--; > + trace_loadvm_approve_switchover(mis->switchover_ack_pending_num); > + > + if (mis->switchover_ack_pending_num) { > + return 0; > + } > + > + return migrate_send_rp_switchover_ack(mis); > +} > + > bool save_snapshot(const char *name, bool overwrite, const char *vmstate, > bool has_devices, strList *devices, Error **errp) > { > diff --git a/migration/trace-events b/migration/trace-events > index cdaef7a1ea..c52b429b28 100644 > --- a/migration/trace-events > +++ b/migration/trace-events > @@ -7,6 +7,7 @@ qemu_loadvm_state_section_partend(uint32_t section_id) "%u" > qemu_loadvm_state_post_main(int ret) "%d" > qemu_loadvm_state_section_startfull(uint32_t section_id, const char *idstr, uint32_t instance_id, uint32_t version_id) "%u(%s) %u %u" > qemu_savevm_send_packaged(void) "" > +loadvm_state_switchover_ack_needed(unsigned int switchover_ack_pending_num) "Switchover ack pending num=%u" > loadvm_state_setup(void) "" > loadvm_state_cleanup(void) "" > loadvm_handle_cmd_packaged(unsigned int length) "%u" > @@ -23,6 +24,7 @@ loadvm_postcopy_ram_handle_discard_end(void) "" > loadvm_postcopy_ram_handle_discard_header(const char *ramid, uint16_t len) "%s: %ud" > loadvm_process_command(const char *s, uint16_t len) "com=%s len=%d" > loadvm_process_command_ping(uint32_t val) "0x%x" > +loadvm_approve_switchover(unsigned int switchover_ack_pending_num) "Switchover ack pending num=%u" > postcopy_ram_listen_thread_exit(void) "" > postcopy_ram_listen_thread_start(void) "" > qemu_savevm_send_postcopy_advise(void) "" > @@ -39,6 +41,7 @@ savevm_send_postcopy_resume(void) "" > savevm_send_colo_enable(void) "" > savevm_send_recv_bitmap(char *name) "%s" > savevm_state_setup(void) "" > +savevm_state_switchover_ack_needed(unsigned int switchover_ack_user_num) "Switchover ack user num=%u" > savevm_state_resume_prepare(void) "" > savevm_state_header(void) "" > savevm_state_iterate(void) "" > @@ -180,6 +183,7 @@ source_return_path_thread_loop_top(void) "" > source_return_path_thread_pong(uint32_t val) "0x%x" > source_return_path_thread_shut(uint32_t val) "0x%x" > source_return_path_thread_resume_ack(uint32_t v) "%"PRIu32 > +source_return_path_thread_switchover_acked(void) "" > migration_thread_low_pending(uint64_t pending) "%" PRIu64 > migrate_transferred(uint64_t tranferred, uint64_t time_spent, uint64_t bandwidth, uint64_t size) "transferred %" PRIu64 " time_spent %" PRIu64 " bandwidth %" PRIu64 " max_size %" PRId64 > process_incoming_migration_co_end(int ret, int ps) "ret=%d postcopy-state=%d" > -- > 2.26.3 > -- Peter Xu