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 04BD7C77B75 for ; Wed, 17 May 2023 09:18:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pzDHe-0001k3-AO; Wed, 17 May 2023 05:17:22 -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 1pzDHc-0001bu-71 for qemu-devel@nongnu.org; Wed, 17 May 2023 05:17:20 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pzDHa-00081U-2a for qemu-devel@nongnu.org; Wed, 17 May 2023 05:17:19 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1684315036; h=from:from: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=FJEksV5MXOCQLN8jdsdn2YjrCJOW5hcW4c5K1GURGjw=; b=h+iokxWFn14sVfS6HXAXuqTP9sti19xeNcW3LDJ+1FDmauD/5lIWpKsyNc7yAi5zw71VGP vhHldUVJ199LP4MZyK6Bbil5R0HMcaWHrlwqEE9IlRxLseerLgjydbtQRtny0EOGRM7mEw I/uK9RrYnO9Ewe7gsjnkH+6km7oMelI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-595-3X3GGVD0PH6FlxCKy1mRIQ-1; Wed, 17 May 2023 05:17:15 -0400 X-MC-Unique: 3X3GGVD0PH6FlxCKy1mRIQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9E41A867946; Wed, 17 May 2023 09:17:14 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.91]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5D9D414171C1; Wed, 17 May 2023 09:17:14 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 561B821E6697; Wed, 17 May 2023 11:17:13 +0200 (CEST) From: Markus Armbruster To: Avihai Horon Cc: , Alex Williamson , =?utf-8?Q?C=C3=A9dric?= Le Goater , Juan Quintela , Peter Xu , Leonardo Bras , Eric Blake , Thomas Huth , Laurent Vivier , Paolo Bonzini , Yishai Hadas , Jason Gunthorpe , Maor Gottlieb , Kirti Wankhede , Tarun Gupta , Joao Martins Subject: Re: [PATCH 1/8] migration: Add precopy initial data capability References: <20230501140141.11743-1-avihaih@nvidia.com> <20230501140141.11743-2-avihaih@nvidia.com> Date: Wed, 17 May 2023 11:17:13 +0200 In-Reply-To: <20230501140141.11743-2-avihaih@nvidia.com> (Avihai Horon's message of "Mon, 1 May 2023 17:01:34 +0300") Message-ID: <87lehn71wm.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@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, 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 Avihai Horon writes: > Migration downtime estimation is calculated based on bandwidth and > remaining migration data. This assumes that loading of migration data in > the destination takes a negligible amount of time and that downtime > depends only on network speed. > > While this may be true for RAM, it's not necessarily true for other > migration users. For example, loading the data of a VFIO device in the > destination might require from the device to allocate resources, prepare > internal data structures and so on. These operations can take a > significant amount of time which can increase migration downtime. > > This patch adds a new capability "precopy initial data" that allows the > source to send initial precopy data and the destination to ACK that this > data has been loaded. Migration will not attempt to stop the source VM > and complete the migration until this ACK is received. > > This will allow migration users to send initial precopy data which can > be used to reduce downtime (e.g., by pre-allocating resources), while > making sure that the source will stop the VM and complete the migration > only after this initial precopy data is sent and loaded in the > destination so it will have full effect. > > This new capability relies on the return path capability to communicate > from the destination back to the source. > > The actual implementation of the capability will be added in the > following patches. > > Signed-off-by: Avihai Horon > --- > qapi/migration.json | 9 ++++++++- > migration/options.h | 1 + > migration/options.c | 20 ++++++++++++++++++++ > 3 files changed, 29 insertions(+), 1 deletion(-) > > diff --git a/qapi/migration.json b/qapi/migration.json > index 82000adce4..d496148386 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -478,6 +478,13 @@ > # should not affect the correctness of postcopy migration. > # (since 7.1) > # > +# @precopy-initial-data: If enabled, migration will not attempt to stop source > +# VM and complete the migration until an ACK is received > +# from the destination that initial precopy data has > +# been loaded. This can improve downtime if there are > +# migration users that support precopy initial data. > +# (since 8.1) > +# Please format like # @precopy-initial-data: If enabled, migration will not attempt to # stop source VM and complete the migration until an ACK is # received from the destination that initial precopy data has been # loaded. This can improve downtime if there are migration users # that support precopy initial data. (since 8.1) to blend in with recent commit a937b6aa739 (qapi: Reformat doc comments to conform to current conventions). What do you mean by "if there are migration users that support precopy initial data"? Do I have to ensure the ACK comes by configuring the destination VM in a certain way, and if yes, how exactly? > # Features: > # @unstable: Members @x-colo and @x-ignore-shared are experimental. > # > @@ -492,7 +499,7 @@ > 'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate', > { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] }, > 'validate-uuid', 'background-snapshot', > - 'zero-copy-send', 'postcopy-preempt'] } > + 'zero-copy-send', 'postcopy-preempt', 'precopy-initial-data'] } > > ## > # @MigrationCapabilityStatus: > diff --git a/migration/options.h b/migration/options.h > index 3c322867cd..d004b6321e 100644 > --- a/migration/options.h > +++ b/migration/options.h > @@ -44,6 +44,7 @@ bool migrate_pause_before_switchover(void); > bool migrate_postcopy_blocktime(void); > bool migrate_postcopy_preempt(void); > bool migrate_postcopy_ram(void); > +bool migrate_precopy_initial_data(void); > bool migrate_rdma_pin_all(void); > bool migrate_release_ram(void); > bool migrate_return_path(void); > diff --git a/migration/options.c b/migration/options.c > index 53b7fc5d5d..c4ef0c60c7 100644 > --- a/migration/options.c > +++ b/migration/options.c > @@ -184,6 +184,8 @@ Property migration_properties[] = { > DEFINE_PROP_MIG_CAP("x-zero-copy-send", > MIGRATION_CAPABILITY_ZERO_COPY_SEND), > #endif > + DEFINE_PROP_MIG_CAP("x-precopy-initial-data", > + MIGRATION_CAPABILITY_PRECOPY_INITIAL_DATA), > > DEFINE_PROP_END_OF_LIST(), > }; > @@ -286,6 +288,13 @@ bool migrate_postcopy_ram(void) > return s->capabilities[MIGRATION_CAPABILITY_POSTCOPY_RAM]; > } > > +bool migrate_precopy_initial_data(void) > +{ > + MigrationState *s = migrate_get_current(); > + > + return s->capabilities[MIGRATION_CAPABILITY_PRECOPY_INITIAL_DATA]; > +} > + > bool migrate_rdma_pin_all(void) > { > MigrationState *s = migrate_get_current(); > @@ -546,6 +555,17 @@ bool migrate_caps_check(bool *old_caps, bool *new_caps, Error **errp) > } > } > > + if (new_caps[MIGRATION_CAPABILITY_PRECOPY_INITIAL_DATA]) { > + if (!new_caps[MIGRATION_CAPABILITY_RETURN_PATH]) { > + error_setg(errp, "Precopy initial data requires return path"); Shouldn't we mention this requirement in the docs? To make sense of the message, the user needs to make the connection from "Precopy initial data" to capability @precopy-initial-data, and from "return path" to capability @return-path. More helpful, I think: "capability 'precopy-initial-data' requires capability 'return-path'". > + return false; > + } > + > + /* Disable this capability until it's implemented */ > + error_setg(errp, "Precopy initial data is not implemented yet"); > + return false; > + } > + > return true; > }