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=-13.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 9F5ECC64E8A for ; Thu, 3 Dec 2020 11:44:52 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id DC08D20758 for ; Thu, 3 Dec 2020 11:44:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DC08D20758 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 ([::1]:47268 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kkn2Y-0001ic-Ga for qemu-devel@archiver.kernel.org; Thu, 03 Dec 2020 06:44:50 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:59152) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kkn1f-00017a-2X for qemu-devel@nongnu.org; Thu, 03 Dec 2020 06:43:55 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:24429) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kkn1d-0001v8-0o for qemu-devel@nongnu.org; Thu, 03 Dec 2020 06:43:54 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606995831; 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=ryQtyvKrMoKqVvbhAcvtjtg4/0PnOzZ6GpZD/Guw8To=; b=T+JC1SQLMud7LoQngMDvWSNjzfq+ZrzkXB0Yn5j9t610Euj/nDKLLQXRIbJ2ELy/ftM5wH qzE3uImavjNPD0E3i7Taok1E7vjlTOAbyvxj5e7irCc0Q916NQzHdVKvUVo7NOl3PcnwLO x1TeWBQTqDQLbTkcRpKw+nyPFS7LNsE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-64-xaiVAUO7MISAsvsrfgTTPw-1; Thu, 03 Dec 2020 06:43:50 -0500 X-MC-Unique: xaiVAUO7MISAsvsrfgTTPw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D8427107AD87 for ; Thu, 3 Dec 2020 11:43:48 +0000 (UTC) Received: from work-vm (ovpn-112-127.ams2.redhat.com [10.36.112.127]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 540C05D6AC; Thu, 3 Dec 2020 11:43:43 +0000 (UTC) Date: Thu, 3 Dec 2020 11:43:41 +0000 From: "Dr. David Alan Gilbert" To: "Michael S. Tsirkin" Subject: Re: [PATCH v2 01/27] migration: Network Failover can't work with a paused guest Message-ID: <20201203114341.GB2919@work-vm> References: <20201202053219-mutt-send-email-mst@kernel.org> <87mtywlbvq.fsf@secure.mitica> <20201202105515.GD2360260@redhat.com> <20201202061641-mutt-send-email-mst@kernel.org> <20201202112639.GE2360260@redhat.com> <20201202063656-mutt-send-email-mst@kernel.org> <20201202120121.GF2360260@redhat.com> <20201203061907-mutt-send-email-mst@kernel.org> <20201203113253.GD2952498@redhat.com> <20201203063452-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: <20201203063452-mutt-send-email-mst@kernel.org> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.495, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Eduardo Habkost , Juan Quintela , Jason Wang , qemu-devel@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Michael S. Tsirkin (mst@redhat.com) wrote: > On Thu, Dec 03, 2020 at 11:32:53AM +0000, Daniel P. Berrangé wrote: > > On Thu, Dec 03, 2020 at 06:21:47AM -0500, Michael S. Tsirkin wrote: > > > On Wed, Dec 02, 2020 at 12:01:21PM +0000, Daniel P. Berrangé wrote: > > > > On Wed, Dec 02, 2020 at 06:37:46AM -0500, Michael S. Tsirkin wrote: > > > > > On Wed, Dec 02, 2020 at 11:26:39AM +0000, Daniel P. Berrangé wrote: > > > > > > On Wed, Dec 02, 2020 at 06:19:29AM -0500, Michael S. Tsirkin wrote: > > > > > > > On Wed, Dec 02, 2020 at 10:55:15AM +0000, Daniel P. Berrangé wrote: > > > > > > > > On Wed, Dec 02, 2020 at 11:51:05AM +0100, Juan Quintela wrote: > > > > > > > > > "Michael S. Tsirkin" wrote: > > > > > > > > > > On Wed, Dec 02, 2020 at 05:31:53AM -0500, Michael S. Tsirkin wrote: > > > > > > > > > >> On Wed, Dec 02, 2020 at 10:27:18AM +0000, Daniel P. Berrangé wrote: > > > > > > > > > >> > On Wed, Dec 02, 2020 at 05:13:18AM -0500, Michael S. Tsirkin wrote: > > > > > > > > > >> > > On Wed, Nov 18, 2020 at 09:37:22AM +0100, Juan Quintela wrote: > > > > > > > > > >> > > > If we have a paused guest, it can't unplug the network VF device, so > > > > > > > > > >> > > > we wait there forever. Just change the code to give one error on that > > > > > > > > > >> > > > case. > > > > > > > > > >> > > > > > > > > > > > > >> > > > Signed-off-by: Juan Quintela > > > > > > > > > >> > > > > > > > > > > > >> > > It's certainly possible but it's management that created > > > > > > > > > >> > > this situation after all - why do we bother to enforce > > > > > > > > > >> > > a policy? It is possible that management will unpause immediately > > > > > > > > > >> > > afterwards and everything will proceed smoothly. > > > > > > > > > >> > > > > > > > > > > > >> > > Yes migration will not happen until guest is > > > > > > > > > >> > > unpaused but the same it true of e.g. a guest that is stuck > > > > > > > > > >> > > because of a bug. > > > > > > > > > >> > > > > > > > > > > >> > That's pretty different behaviour from how migration normally handles > > > > > > > > > >> > a paused guest, which is that it is guaranteed to complete the migration > > > > > > > > > >> > in as short a time as network bandwidth allows. > > > > > > > > > >> > > > > > > > > > > >> > Just ignoring the situation I think will lead to surprise apps / admins, > > > > > > > > > >> > because the person/entity invoking the migration is not likely to have > > > > > > > > > >> > checked wether this particular guest uses net failover or not before > > > > > > > > > >> > invoking - they'll just be expecting a paused migration to run fast and > > > > > > > > > >> > be guaranteed to complete. > > > > > > > > > >> > > > > > > > > > > >> > Regards, > > > > > > > > > >> > Daniel > > > > > > > > > >> > > > > > > > > > >> Okay I guess. But then shouldn't we handle the reverse situation too: > > > > > > > > > >> pausing guest after migration started but before device was > > > > > > > > > >> unplugged? > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > Thinking of which, I have no idea how we'd handle it - fail > > > > > > > > > > pausing guest until migration is cancelled? > > > > > > > > > > > > > > > > > > > > All this seems heavy handed to me ... > > > > > > > > > > > > > > > > > > This is the minimal fix that I can think of. > > > > > > > > > > > > > > > > > > Further solution would be: > > > > > > > > > - Add a new migration parameter: migrate-paused > > > > > > > > > - change libvirt to use the new parameter if it exist > > > > > > > > > - in qemu, when we do start migration (but after we wait for the unplug > > > > > > > > > device) paused the guest before starting migration and resume it after > > > > > > > > > migration finish. > > > > > > > > > > > > > > > > It would also have to handle issuing of paused after migration has > > > > > > > > been started - delay the pause request until the nuplug is complete > > > > > > > > is one answer. > > > > > > > > > > > > > > Hmm my worry would be that pausing is one way to give cpu > > > > > > > resources back to host. It's problematic if guest can delay > > > > > > > that indefinitely. > > > > > > > > > > > > hmm, yes, that is awkward. Perhaps we should just report an explicit > > > > > > error then. > > > > > > > > > > Report an error in response to which command? Do you mean > > > > > fail migration? > > > > > > > > If mgt attempt to pause an existing migration that hasn't finished > > > > the PCI unplug stage, then fail the pause request. > > > > > > Pause guest not migration ... > > > Might be tricky ... > > > > > > Let me ask this, why not just produce a warning > > > that migration wan't finish until guest actually runs? > > > User will then know and unpause the guest when he wants > > > migration to succeed ... > > > > A warning is going to be essentally invisible if the pause command > > succeeeds. > > > > Regards, > > Daniel > > I mean the situation here isn't earth shattering, an admin > created it. Maybe he will unpause shortly > and all will be well ... > > How about we make it possible for admin to detect that the > reason for migration not making progress is that it is > waiting for unplug? And maybe that guest is paused too? We already know that from the state of the VM. > I just don't see how we can detect all cases and I am not > sure it is worth it to try and detect only some of them, > making users think they can rely on command failure to > detect them. Another way to solve this would be to remove the unplugging from the migration layer and leave it as a problem for the management layer to do the unplug. Dave > > > -- > > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > > |: https://libvirt.org -o- https://fstop138.berrange.com :| > > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK