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 CB9ACCAC59A for ; Fri, 19 Sep 2025 12:06:18 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uzZrY-0008Ap-Nc; Fri, 19 Sep 2025 08:05:16 -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 1uzZr8-0007y2-AG for qemu-devel@nongnu.org; Fri, 19 Sep 2025 08:04:52 -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 1uzZr2-0006lP-7S for qemu-devel@nongnu.org; Fri, 19 Sep 2025 08:04:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758283464; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VfEZK7k8xoSg2IiXntacZ3MMUI62+Jt/3fFuwo7O2MI=; b=LA193+BoZB+99LbgUfPfdnv58EvFtNJfsznzVRpg26JQYYN03VW5KvGzGDOu9mlqf8sf4p 5xJdTsyABQQQ9gZddcrOJkqNsqLksdNsVNPmI1GHHAS24ypcNVapdAOxMcO2g4eyYHn05C t+Hwq7GSBOJ/XTlxbS+vcqqSGB09o+A= Received: from mx-prod-mc-06.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-578-SGhr9CwCMvC0mIyNzMoD3Q-1; Fri, 19 Sep 2025 08:04:23 -0400 X-MC-Unique: SGhr9CwCMvC0mIyNzMoD3Q-1 X-Mimecast-MFC-AGG-ID: SGhr9CwCMvC0mIyNzMoD3Q_1758283462 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-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6CB6E1800378; Fri, 19 Sep 2025 12:04:22 +0000 (UTC) Received: from orkuz (unknown [10.44.34.9]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 9616B1800446; Fri, 19 Sep 2025 12:04:21 +0000 (UTC) Date: Fri, 19 Sep 2025 14:04:19 +0200 From: =?utf-8?B?SmnFmcOt?= Denemark To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: Juraj Marcin , Peter Xu , qemu-devel@nongnu.org, Fabiano Rosas Subject: Re: [PATCH] migration: Apply migration specific keep-alive defaults to inet socket Message-ID: References: <20250909150127.1494626-1-jmarcin@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; envelope-from=jdenemar@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.105, 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_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_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: 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 Thu, Sep 18, 2025 at 15:45:21 +0100, Daniel P. Berrangé wrote: > On Thu, Sep 18, 2025 at 04:16:56PM +0200, Juraj Marcin wrote: > > If there is no outgoing traffic from the destination side (this can be > > caused for example by a workload with no page faults or paused machine), > > QEMU has no way of knowing if the connection is still working or not. > > The TCP stack doesn't treat no incoming traffic as a sign of a broken > > connection. Therefore, QEMU would stay in postcopy-active waiting for > > pages indefinitely. > > > > Also, libvirt might not be aware of a connection dropout between QEMUs, > > if libvirt's connection is intact, especially if libvirt daemons are > > communicating through some central entity that is managing the migration > > and not directly. And to do postcopy migration recovery, libvirt needs > > both sides to be in postcopy-paused state. > > Whether keepalive timeouts are at the QEMU level or global kernel > level, there will always be situations where the timeouts are too > long. Apps/admins can have out of band liveliness checks between > hosts that detect a problem before the keepalives will trigger > and shouldn't have to wait to recover migration, once they have > resolved the underlying network issue. > > There needs to be a way to initiate post-copy recovery regardless > of whether we've hit a keepalive timeout. Especially if we can > see one QEMU in postcopy-paused, but not the other side, it > doesn't appear to make sense to block the recovery process. > > The virDomainJobCancel command can do a migrate-cancel on the > src, but it didn't look like we could do the same on the dst. > Unless I've overlooked something, Libvirt needs to gain a way > to explicitly force both sides into the postcopy-paused state, > and thus be able to immediately initiate recovery. > > > Alternatively, there also might be an issue with the connection between > > libvirt daemons, but not the migration connection. Even if the libvirt > > connection fails, the migration is not paused, rather libvirt lets the > > migration finish normally. Similarly, if the libvirt connection is > > broken up due to, for example, libvirt daemon restart, the ongoing > > migration is not paused, but after the libvirt daemon starts again, it > > sees an ongoing migration and lets it finish. > > Whole this is a reliability issue for libvirt, this doesn't have > any bearing on migration keepalive timeouts, as we're only concerned > about QEMU connections. > > > Additionally, libvirt uses its own internal keep-alive packets with much > > more aggressive timeouts, waiting 5 - 10 seconds idle before sending a > > keep-alive packet and then killing the connection if there is no > > response in 30 seconds. > > Yep, this keepalive is very aggressive and has frequently caused > problems with libvirt connections being torn down inappropriately. This was happening when a link was saturated with storage migrations and the keepalive messages in a separate (and otherwise idle) connection were not sent in time. We haven't seen any reports for quite some time. I believe it was identified as a kernel bug a few years ago and then the reports stopped. Jirka