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 E5FF8E95396 for ; Wed, 4 Feb 2026 13:25:34 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vncsV-0007eo-VG; Wed, 04 Feb 2026 08:25:07 -0500 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 1vncsU-0007d0-Ot for qemu-devel@nongnu.org; Wed, 04 Feb 2026 08:25:06 -0500 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 1vncsT-0003Xt-2y for qemu-devel@nongnu.org; Wed, 04 Feb 2026 08:25:06 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1770211504; 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=jO6Oag8JvgEdSrQFiblwJ20INZ+9aQQEIsf3Gd2bFMM=; b=X1p6TTIa05v6VBYH9xO3d6OU0D17uWn7w8RqhY6P6Aa8nPxfqo1ViJ3v/5vswSzbEZEjYp q2i7COwH94+Ou3SHFduPvUFRMzkgxLqxnNWsbV1imVIgSx1Zv9aEE3YyZ0Bcqj/v4ebWz2 Qc7PC7xm0mwvK9/CrUZtWIpgBE8ARmU= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-196-sbELeB7vP2C9Bh0gf0vnEQ-1; Wed, 04 Feb 2026 08:25:01 -0500 X-MC-Unique: sbELeB7vP2C9Bh0gf0vnEQ-1 X-Mimecast-MFC-AGG-ID: sbELeB7vP2C9Bh0gf0vnEQ_1770211500 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BE4DB1800454; Wed, 4 Feb 2026 13:24:59 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.22]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4701A1800465; Wed, 4 Feb 2026 13:24:59 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id EADCF21E692D; Wed, 04 Feb 2026 14:24:56 +0100 (CET) From: Markus Armbruster To: Avihai Horon Cc: , Alex Williamson , =?utf-8?Q?C=C3=A9dric?= Le Goater , Eric Blake , Peter Xu , Fabiano Rosas , Maor Gottlieb Subject: Re: [PATCH v3] vfio/migration: Send VFIO_MIGRATION event before PRE_COPY_P2P transition In-Reply-To: <87jywswslz.fsf@pond.sub.org> (Markus Armbruster's message of "Wed, 04 Feb 2026 14:22:48 +0100") References: <20260202173406.13979-1-avihaih@nvidia.com> <87jywswslz.fsf@pond.sub.org> Date: Wed, 04 Feb 2026 14:24:56 +0100 Message-ID: <87ecn0wsif.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; 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, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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 Markus Armbruster writes: > Avihai Horon writes: > >> The VFIO_MIGRATION event notifies users when a VFIO device transitions >> to a new state. >> >> One use case for this event is to prevent timeouts for RDMA connections >> to the migrated device. In this case, an external management application >> (not libvirt) consumes the events and disables the RDMA timeout >> mechanism when receiving the event for PRE_COPY_P2P state, which >> indicates that the device is non-responsive. >> >> This is essential because RDMA connections typically have very low >> timeouts (tens of milliseconds), which can be far below migration >> downtime. >> >> However, under heavy resource utilization, the device transition to >> PRE_COPY_P2P can take hundreds of milliseconds to complete. Since the >> VFIO_MIGRATION event is currently sent only after the transition >> completes, it arrives too late, after RDMA connections have already >> timed out. >> >> To address this, send an additional "prepare" event immediately before >> initiating the PRE_COPY_P2P transition. This guarantees timely event >> delivery regardless of how long the actual state transition takes. >> >> Signed-off-by: Avihai Horon > > [...] > >> diff --git a/qapi/vfio.json b/qapi/vfio.json >> index a1a9c5b673..17b6046871 100644 >> --- a/qapi/vfio.json >> +++ b/qapi/vfio.json >> @@ -11,7 +11,13 @@ >> ## >> # @QapiVfioMigrationState: >> # >> -# An enumeration of the VFIO device migration states. >> +# An enumeration of the VFIO device migration states. In addition to >> +# the regular states, there are prepare states (with 'prepare' suffix) >> +# which indicate that the device is just about to transition to the >> +# corresponding state. Note that seeing a prepare state for state X >> +# doesn't guarantee that the next state will be X, as the state >> +# transition can fail and the device may transition to a different >> +# state instead. >> # >> # @stop: The device is stopped. >> # >> @@ -32,11 +38,14 @@ >> # tracking its internal state and its internal state is available >> # for reading. >> # >> +# @pre-copy-p2p-prepare: The device is just about to move to >> +# pre-copy-p2p state. (since 11.0) >> +# >> # Since: 9.1 >> ## >> { 'enum': 'QapiVfioMigrationState', >> 'data': [ 'stop', 'running', 'stop-copy', 'resuming', 'running-p2p', >> - 'pre-copy', 'pre-copy-p2p' ] } >> + 'pre-copy', 'pre-copy-p2p', 'pre-copy-p2p-prepare' ] } >> >> ## >> # @VFIO_MIGRATION: > > Acked-by: Markus Armbruster Except for the subject line: "vfio/migration: Send VFIO_MIGRATION event before PRE_COPY_P2P transition" become misleading in v2. > > [...]