From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2A377C7EE29 for ; Fri, 2 Jun 2023 11:15:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1q52jt-00061Z-4j; Fri, 02 Jun 2023 07:14:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1q52jo-00061K-Oo for qemu-devel@nongnu.org; Fri, 02 Jun 2023 07:14:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1q52jm-0007mk-7G for qemu-devel@nongnu.org; Fri, 02 Jun 2023 07:14:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685704469; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=NW74sOm51pWT1PbNAz0N1AThE8xJ1AybxDxtAYveYGM=; b=Ii/KFe+FEILvn2g2AP3ftcEssurjzzOGfInuBWiHYMl9lbsVZ1mwCMQr0XkKgO8szFpB/l xtMXLVQSk3+1UHMCS4pLhuQLyw0zvBo9MNPfsYte91AsoZoNjVXEEyKPAtnDU5mfIzfwd+ spFaI2udx+c2cldU081GgxIt4UdoXlg= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-478-5oVpeVjtOmu1FG501FlyfA-1; Fri, 02 Jun 2023 07:14:28 -0400 X-MC-Unique: 5oVpeVjtOmu1FG501FlyfA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CCEF5380662F; Fri, 2 Jun 2023 11:14:27 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.158]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DE23E2026D49; Fri, 2 Jun 2023 11:14:23 +0000 (UTC) Date: Fri, 2 Jun 2023 12:14:20 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: qemu-devel@nongnu.org, Avihai Horon , Paolo Bonzini , Leonardo Bras Soares Passos , Juan Quintela , Laurent Vivier , Thomas Huth Subject: Re: [PATCH RFC 1/3] migration: switchover-hold parameter Message-ID: References: <20230602011626.226640-1-peterx@redhat.com> <20230602011626.226640-2-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230602011626.226640-2-peterx@redhat.com> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.166, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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, Jun 01, 2023 at 09:16:24PM -0400, Peter Xu wrote: > Add a new migration parameter switchover-hold which can block src qemu > migration from switching over to dest from running. > > One can set this flag to true so src qemu will keep iterating the VM data, > not switching over to dest even if it can. > > It means now live migration works somehow like COLO; we keep syncing data > from src to dst without stopping. > > When the user is ready for the switchover, one can set the parameter from > true->false. That'll contain a implicit kick to migration thread to be > alive and re-evaluate the switchover decision. > > This can be used in two cases so far in my mind: > > (1) One can use this parameter to start pre-heating migration (but not > really migrating, so a migrate-cancel will cancel the preheat). When > the user wants to really migrate, just clear the flag. It'll in most > cases migrate immediately because most pages are already synced. > > (2) Can also be used as a clean way to do qtest, in many of the precopy > tests we have requirement to run after 1 iteration without completing > the precopy migration. Before that we have either set bandwidth to > ridiculous low value, or tricks on detecting guest memory change over > some adhoc guest memory position. Now we can simply set this flag > then we know precopy won't complete and will just keep going. > > Signed-off-by: Peter Xu > --- > qapi/migration.json | 25 +++++++++++++-- > migration/migration.h | 7 +++++ > migration/migration-hmp-cmds.c | 3 ++ > migration/migration.c | 56 ++++++++++++++++++++++++++++++++-- > migration/options.c | 17 +++++++++++ > 5 files changed, 102 insertions(+), 6 deletions(-) > > diff --git a/qapi/migration.json b/qapi/migration.json > index 179af0c4d8..1d0059d125 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -779,6 +779,15 @@ > # Nodes are mapped to their block device name if there is one, and > # to their node name otherwise. (Since 5.2) > # > +# @switchover-hold: Whether we should hold-off precopy switchover from src > +# to dest QEMU, even if we can finish migration in the downtime > +# specified. By default off, so precopy migration will complete as > +# soon as possible. One can set it to explicitly keep iterating during > +# precopy migration until set the flag to false again to kick off the > +# final switchover. Note, this does not affect postcopy switchover, > +# because the user can control that using "migrate-start-postcopy" > +# command explicitly. (Since 8.1) > +# > # Features: > # > # @unstable: Member @x-checkpoint-delay is experimental. > @@ -800,7 +809,7 @@ > 'xbzrle-cache-size', 'max-postcopy-bandwidth', > 'max-cpu-throttle', 'multifd-compression', > 'multifd-zlib-level' ,'multifd-zstd-level', > - 'block-bitmap-mapping' ] } > + 'block-bitmap-mapping', 'switchover-hold' ] } > > ## > # @MigrateSetParameters: > @@ -935,6 +944,10 @@ > # Nodes are mapped to their block device name if there is one, and > # to their node name otherwise. (Since 5.2) > # > +# @switchover-hold: Whether we should hold-off precopy switchover from src > +# to dest QEMU. For more details, please refer to MigrationParameter > +# entry of the same field. (Since 8.1) > +# > # Features: > # > # @unstable: Member @x-checkpoint-delay is experimental. > @@ -972,7 +985,8 @@ > '*multifd-compression': 'MultiFDCompression', > '*multifd-zlib-level': 'uint8', > '*multifd-zstd-level': 'uint8', > - '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } } > + '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ], > + '*switchover-hold': 'bool' } } > > ## > # @migrate-set-parameters: > @@ -1127,6 +1141,10 @@ > # Nodes are mapped to their block device name if there is one, and > # to their node name otherwise. (Since 5.2) > # > +# @switchover-hold: Whether we should hold-off precopy switchover from src > +# to dest QEMU. For more details, please refer to MigrationParameter > +# entry of the same field. (Since 8.1) > +# > # Features: > # > # @unstable: Member @x-checkpoint-delay is experimental. > @@ -1161,7 +1179,8 @@ > '*multifd-compression': 'MultiFDCompression', > '*multifd-zlib-level': 'uint8', > '*multifd-zstd-level': 'uint8', > - '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ] } } > + '*block-bitmap-mapping': [ 'BitmapMigrationNodeAlias' ], > + '*switchover-hold': 'bool' } } > > ## > # @query-migrate-parameters: > diff --git a/migration/migration.h b/migration/migration.h > index 48a46123a0..086ceec754 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -437,6 +437,13 @@ struct MigrationState { > > /* QEMU_VM_VMDESCRIPTION content filled for all non-iterable devices. */ > JSONWriter *vmdesc; > + /* > + * Only migration thread will wait on it when switchover_hold==true. > + * > + * Only qmp set param will kick it when switching switchover_hold from > + * true->false. > + */ > + QemuSemaphore switchover_hold_sem; > }; > > void migrate_set_state(int *state, int old_state, int new_state); > diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c > index 9885d7c9f7..63a2c8a4a3 100644 > --- a/migration/migration-hmp-cmds.c > +++ b/migration/migration-hmp-cmds.c > @@ -338,6 +338,9 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict) > monitor_printf(mon, "%s: '%s'\n", > MigrationParameter_str(MIGRATION_PARAMETER_TLS_AUTHZ), > params->tls_authz); > + monitor_printf(mon, "%s: %s\n", > + MigrationParameter_str(MIGRATION_PARAMETER_SWITCHOVER_HOLD), > + params->switchover_hold ? "on" : "off"); > > if (params->has_block_bitmap_mapping) { > const BitmapMigrationNodeAliasList *bmnal; > diff --git a/migration/migration.c b/migration/migration.c > index 5de7f734b9..30f165527b 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -2700,6 +2700,55 @@ static void migration_update_counters(MigrationState *s, > bandwidth, s->threshold_size); > } > > +static bool > +migration_should_complete(MigrationState *s, uint64_t pending_size) > +{ > + /* We still have large pending data to send? */ > + if (pending_size && (pending_size >= s->threshold_size)) { > + return false; > + } > + > + /* The user doesn't want us to switchover yet */ > + if (s->parameters.switchover_hold) { > + /* > + * Note: when reaching here it probably means we've migrated almost > + * everything and ready to switchover. If user asked not to switch > + * wait for a short period and respond to kicks immediately. > + * > + * If we wait too long, there can be a lot of dirty data generated, > + * while we could have done something to sync data between src/dst. > + * > + * If we wait too short, migration thread can eat most/all cpu > + * resource looping over switchover_hold. > + * > + * Make it 10ms which seems to be a good intermediate value. > + */ > + qemu_sem_timedwait(&s->switchover_hold_sem, 10); > + > + /* > + * Return false here always even if user changed it, because we'd > + * like to re-evaluate everything (e.g. pending_size). > + */ > + return false; > + } > + > + return true; > +} > + > +static bool > +migration_should_start_postcopy(MigrationState *s, uint64_t must_precopy) > +{ > + /* If we're already in postcopy phase, don't bother */ > + if (migration_in_postcopy()) { > + return false; > + } > + /* We still have lots of thing that must be migrated in precopy */ > + if (must_precopy > s->threshold_size) { > + return false; > + } > + return qatomic_read(&s->start_postcopy); > +} > + > /* Migration thread iteration status */ > typedef enum { > MIG_ITERATE_RESUME, /* Resume current iteration */ > @@ -2727,15 +2776,14 @@ 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 (migration_should_complete(s, pending_size)) { > 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 && > - qatomic_read(&s->start_postcopy)) { > + if (migration_should_start_postcopy(s, must_precopy)) { > if (postcopy_start(s)) { > error_report("%s: postcopy failed to start", __func__); > } > @@ -3287,6 +3335,7 @@ static void migration_instance_finalize(Object *obj) > qemu_sem_destroy(&ms->rp_state.rp_sem); > qemu_sem_destroy(&ms->rp_state.rp_pong_acks); > qemu_sem_destroy(&ms->postcopy_qemufile_src_sem); > + qemu_sem_destroy(&ms->switchover_hold_sem); > error_free(ms->error); > } > > @@ -3309,6 +3358,7 @@ static void migration_instance_init(Object *obj) > qemu_sem_init(&ms->rate_limit_sem, 0); > qemu_sem_init(&ms->wait_unplug_sem, 0); > qemu_sem_init(&ms->postcopy_qemufile_src_sem, 0); > + qemu_sem_init(&ms->switchover_hold_sem, 0); > qemu_mutex_init(&ms->qemu_file_lock); > } > > diff --git a/migration/options.c b/migration/options.c > index b62ab30cd5..2d6b138352 100644 > --- a/migration/options.c > +++ b/migration/options.c > @@ -163,6 +163,8 @@ Property migration_properties[] = { > DEFINE_PROP_STRING("tls-creds", MigrationState, parameters.tls_creds), > DEFINE_PROP_STRING("tls-hostname", MigrationState, parameters.tls_hostname), > DEFINE_PROP_STRING("tls-authz", MigrationState, parameters.tls_authz), > + DEFINE_PROP_BOOL("switchover-hold", MigrationState, > + parameters.switchover_hold, false), > > /* Migration capabilities */ > DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE), > @@ -883,6 +885,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp) > params->announce_rounds = s->parameters.announce_rounds; > params->has_announce_step = true; > params->announce_step = s->parameters.announce_step; > + params->has_switchover_hold = true; > + params->switchover_hold = s->parameters.switchover_hold; > > if (s->parameters.has_block_bitmap_mapping) { > params->has_block_bitmap_mapping = true; > @@ -923,6 +927,7 @@ void migrate_params_init(MigrationParameters *params) > params->has_announce_max = true; > params->has_announce_rounds = true; > params->has_announce_step = true; > + params->has_switchover_hold = true; > } > > /* > @@ -1177,6 +1182,9 @@ static void migrate_params_test_apply(MigrateSetParameters *params, > if (params->has_announce_step) { > dest->announce_step = params->announce_step; > } > + if (params->has_switchover_hold) { > + dest->switchover_hold = params->switchover_hold; > + } > > if (params->has_block_bitmap_mapping) { > dest->has_block_bitmap_mapping = true; > @@ -1290,6 +1298,15 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp) > if (params->has_announce_step) { > s->parameters.announce_step = params->announce_step; > } > + if (params->has_switchover_hold) { > + bool old = s->parameters.switchover_hold; > + bool new = params->switchover_hold; > + > + s->parameters.switchover_hold = params->switchover_hold; > + if (old && !new) { > + qemu_sem_post(&s->switchover_hold_sem); > + } > + } IIUC, MigrationState is global to QEMU and gets reused on every migration. If we qemu_sem_post() here, and the migration fails, and the user starts a new migration on the same QEMU, the switchover_hold_sem needs resetting somewhere, as there's a (tiny) risk that the qemu_sem_timedwait() won't have run before the migration fail. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|