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 B4DBAE9539D for ; Wed, 4 Feb 2026 13:23:39 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vncqZ-0003Sr-9A; Wed, 04 Feb 2026 08:23:07 -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 1vncqP-0003Lu-R1 for qemu-devel@nongnu.org; Wed, 04 Feb 2026 08:22:58 -0500 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 1vncqN-000338-V4 for qemu-devel@nongnu.org; Wed, 04 Feb 2026 08:22:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1770211374; 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=A/g6KjAiQZk+xb8sc5e1aTQWLKu0s6V9lTsUfrosO08=; b=VC50RNZz0ltBZNc992c1jB9sY6mVLlnwfwJOGYHis4rI/N4KVYYPAoz+99daZqG8sNruJt cMg8bCXVPFX6/0cjg8ODsc/j+uJlDnG1ssjmIB63Edj2tPk0RAu14KA7oaVI2WrE/fW15q O99qVQyGSFP4qVys8qmzopnKWwlYyak= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-313-25zX8RY5NqSWyND7qZWcRg-1; Wed, 04 Feb 2026 08:22:52 -0500 X-MC-Unique: 25zX8RY5NqSWyND7qZWcRg-1 X-Mimecast-MFC-AGG-ID: 25zX8RY5NqSWyND7qZWcRg_1770211371 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BCAF219560B2; Wed, 4 Feb 2026 13:22:51 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.22]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7849118003F6; Wed, 4 Feb 2026 13:22:51 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 02C5321E692D; Wed, 04 Feb 2026 14:22:49 +0100 (CET) From: Markus Armbruster To: Avihai Horon Cc: , Alex Williamson , =?utf-8?Q?C=C3=A9dric?= Le Goater , Eric Blake , Markus Armbruster , Peter Xu , Fabiano Rosas , Maor Gottlieb Subject: Re: [PATCH v3] vfio/migration: Send VFIO_MIGRATION event before PRE_COPY_P2P transition In-Reply-To: <20260202173406.13979-1-avihaih@nvidia.com> (Avihai Horon's message of "Mon, 2 Feb 2026 19:34:06 +0200") References: <20260202173406.13979-1-avihaih@nvidia.com> Date: Wed, 04 Feb 2026 14:22:48 +0100 Message-ID: <87jywswslz.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 10.30.177.111 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, 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 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 [...]