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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,T_HK_NAME_DR,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 01F7DC282CE for ; Tue, 4 Jun 2019 19:02:05 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CFA792075C for ; Tue, 4 Jun 2019 19:02:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CFA792075C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([127.0.0.1]:56581 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hYEh9-0002DK-S5 for qemu-devel@archiver.kernel.org; Tue, 04 Jun 2019 15:02:03 -0400 Received: from eggs.gnu.org ([209.51.188.92]:43824) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hYEg1-0001hi-VC for qemu-devel@nongnu.org; Tue, 04 Jun 2019 15:00:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hYEg0-00073A-O7 for qemu-devel@nongnu.org; Tue, 04 Jun 2019 15:00:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42010) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hYEg0-0006s1-Eb for qemu-devel@nongnu.org; Tue, 04 Jun 2019 15:00:52 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D246C7EBC4 for ; Tue, 4 Jun 2019 19:00:31 +0000 (UTC) Received: from work-vm (ovpn-117-216.ams2.redhat.com [10.36.117.216]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4562B60C91; Tue, 4 Jun 2019 19:00:21 +0000 (UTC) Date: Tue, 4 Jun 2019 20:00:19 +0100 From: "Dr. David Alan Gilbert" To: "Michael S. Tsirkin" Message-ID: <20190604190019.GM3851@work-vm> References: <20190517125820.2885-1-jfreimann@redhat.com> <20190517125820.2885-4-jfreimann@redhat.com> <20190521094504.GB2915@work-vm> <20190530145645.tjwkgi4hae5yblsi@jenstp.localdomain> <20190531214748.GN22103@habkost.net> <20190603082456.vzpy256kj4o5e5wu@jenstp.localdomain> <20190603193648.GQ22103@habkost.net> <20190604134321.txlw7wjwe247g5ug@jenstp.localdomain> <20190604125037-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190604125037-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.11.4 (2019-03-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 04 Jun 2019 19:00:31 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 3/4] net/virtio: add failover support X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pkrempa@redhat.com, berrange@redhat.com, Eduardo Habkost , aadam@redhat.com, qemu-devel@nongnu.org, laine@redhat.com, Jens Freimann , ailan@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Michael S. Tsirkin (mst@redhat.com) wrote: > On Tue, Jun 04, 2019 at 03:43:21PM +0200, Jens Freimann wrote: > > On Mon, Jun 03, 2019 at 04:36:48PM -0300, Eduardo Habkost wrote: > > > On Mon, Jun 03, 2019 at 10:24:56AM +0200, Jens Freimann wrote: > > > > On Fri, May 31, 2019 at 06:47:48PM -0300, Eduardo Habkost wrote: > > > > > On Thu, May 30, 2019 at 04:56:45PM +0200, Jens Freimann wrote: > > > > > > On Tue, May 28, 2019 at 11:04:15AM -0400, Michael S. Tsirkin wrote: > > > > > > > On Tue, May 21, 2019 at 10:45:05AM +0100, Dr. David Alan Gilbert wrote: > > > > > > > > * Jens Freimann (jfreimann@redhat.com) wrote: > > > > Why is it bad to fully re-create the device in case of a failed migration? > > > > > > Bad or not, I thought the whole point of doing it inside QEMU was > > > to do something libvirt wouldn't be able to do (namely, > > > unplugging the device while not freeing resources). If we are > > > doing something that management software is already capable of > > > doing, what's the point? > > > > Event though management software seems to be capable of it, a failover > > implementation has never happened. As Michael says network failover is > > a mechanism (there's no good reason not to use a PT device if it is > > available), not a policy. We are now trying to implement it in a > > simple way, contained within QEMU. > > > > > Quoting a previous message from this thread: > > > > > > On Thu, May 30, 2019 at 02:09:42PM -0400, Michael S. Tsirkin wrote: > > > | > On Thu, May 30, 2019 at 07:00:23PM +0100, Dr. David Alan Gilbert wrote: > > > | > > This patch series is very > > > | > > odd precisely because it's trying to do the unplug itself in the > > > | > > migration phase rather than let the management layer do it - so unless > > > | > > it's nailed down how to make sure that's really really bullet proof > > > | > > then we've got to go back and ask the question about whether we should > > > | > > really fix it so it can be done by the management layer. > > > | > > > > > | > > Dave > > > | > > > > | > management already said they can't because files get closed and > > > | > resources freed on unplug and so they might not be able to re-add device > > > | > on migration failure. We do it in migration because that is > > > | > where failures can happen and we can recover. > > > > This is something that I can work on as well, but it doesn't have to > > be part of this patch set in my opinion. Let's say migration fails and we can't > > re-plug the primary device. We can still use the standby (virtio-net) > > device which would only mean slower networking. How likely is it that > > the primary device is grabbed by another VM between unplugging and > > migration failure anyway? > > > > regards, > > Jens > > I think I agree with Eduardo it's very important to handle this corner > case correctly. Fast networking outside migration is why people use > failover at all. Someone who can live with a slower virtio would use > just that. > > And IIRC this corner case is exactly why libvirt could not > implement it correctly itself and had to push it up the stack > until it fell off the cliff :). So I think we need to have the code that shows we can cope with the corner cases - or provide a way for libvirt to handle it (which is my strong preference). Dave > > > > > > > > -- > > > Eduardo -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK