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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 43993C43460 for ; Tue, 20 Apr 2021 15:21:41 +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 660A361354 for ; Tue, 20 Apr 2021 15:21:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 660A361354 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]:60228 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lYsC3-0004j5-4o for qemu-devel@archiver.kernel.org; Tue, 20 Apr 2021 11:21:39 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49812) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYsAu-00043P-Al for qemu-devel@nongnu.org; Tue, 20 Apr 2021 11:20:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:52916) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lYsAi-0003TS-6k for qemu-devel@nongnu.org; Tue, 20 Apr 2021 11:20:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618932012; 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=4ubl9qwL3Y+dqyae1iZlSqKoeE0lHArlEayAUKR5+zs=; b=K7kku8HxE1sIUrieHf7WdikQkjWLntnfa3IDSnOg62MGa/IUtJiBghzZOyAWs5qQmLSFPc qdf9lGnuk82UUe2au4CG/KZBb9wwzz2FHcgrRyJHBtsIAJ3iFwIt9pqpngXbfpfjCF7xeT K351jwoDCknCcd5CGJly+IfkarUt4yE= 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-453-lxqmU1FFPPKOhNOYRbkMtA-1; Tue, 20 Apr 2021 11:20:10 -0400 X-MC-Unique: lxqmU1FFPPKOhNOYRbkMtA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 150D38542C8 for ; Tue, 20 Apr 2021 15:20:10 +0000 (UTC) Received: from localhost (ovpn-118-208.rdu2.redhat.com [10.10.118.208]) by smtp.corp.redhat.com (Postfix) with ESMTP id BACC819D80; Tue, 20 Apr 2021 15:20:09 +0000 (UTC) Date: Tue, 20 Apr 2021 11:20:09 -0400 From: Eduardo Habkost To: "Dr. David Alan Gilbert" Subject: Re: [PATCH RFC] migration: warn about non-migratable configurations unless '--no-migration' was specified Message-ID: <20210420152009.imao3srwmskpcmbw@habkost.net> References: <874kg68z07.fsf@vitty.brq.redhat.com> <20210416162801.zluqlbvyipoanedw@habkost.net> <20210419193228.q5e6vdnqwygh22bq@habkost.net> <20210420134811.o2ypiw3y4fr73udb@habkost.net> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=ehabkost@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=216.205.24.124; envelope-from=ehabkost@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, 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 =?utf-8?B?UC4gQmVycmFuZ8Op?= , Juan Quintela , qemu-devel@nongnu.org, Markus Armbruster , Paolo Bonzini , Vitaly Kuznetsov Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Apr 20, 2021 at 03:10:44PM +0100, Dr. David Alan Gilbert wrote: > * Eduardo Habkost (ehabkost@redhat.com) wrote: > > On Tue, Apr 20, 2021 at 12:51:43PM +0100, Dr. David Alan Gilbert wrote: > > > * Eduardo Habkost (ehabkost@redhat.com) wrote: > > > > On Mon, Apr 19, 2021 at 07:47:34PM +0100, Dr. David Alan Gilbert wrote: > > > > > * Daniel P. Berrangé (berrange@redhat.com) wrote: > > > > > > On Mon, Apr 19, 2021 at 06:15:56PM +0100, Daniel P. Berrangé wrote: > > > > > > > On Mon, Apr 19, 2021 at 06:11:47PM +0100, Dr. David Alan Gilbert wrote: > > > > > > > > * Eduardo Habkost (ehabkost@redhat.com) wrote: > > > > > > > > > I would make live migration policy an enum, just to make sure > > > > > > > > > we are explicit about the requirements: > > > > > > > > > > > > > > > > > > - UNKNOWN: this is the current state in QEMU 6.0, where we don't > > > > > > > > > really know what the user expects. > > > > > > > > > This can be the default on existing versioned machine types, > > > > > > > > > just for compatibility. > > > > > > > > > I suggest making this print warnings for every migration > > > > > > > > > blocker (like this patch does). > > > > > > > > > I suggest deprecating this behavior as soon as we can. > > > > > > > > > > > > > > > > > > - PREFERRED: try to make the VM migratable when possible, but > > > > > > > > > don't print a warning or error out if migration is blocked. > > > > > > > > > This seems to be the behavior expected by libvirt today. > > > > > > > > > > > > > > > > > > - NOT_NEEDED: live migration is not needed, and QEMU is free to > > > > > > > > > enable features that block live migration or change guest ABI. > > > > > > > > > We can probably make this the default on machine types that > > > > > > > > > never supported live migration. > > > > > > > > > > > > > > > > I suggest you could do this by adding: > > > > > > > > -warn-none-migratable > > > > > > > > -no-warn-none-migratable > > > > > > > > > > > > > > > > and then argue about defaults another time. > > > > > > > > > > > > > > If we're going to add new args, lets at least future proof our > > > > > > > approach with an extensible option that we can wire into QMP > > > > > > > too later > > > > > > > > > > > > > > -migratable none|preferred|required > > > > > > > > > > > > > > and letting us add extra key/value pairs to tune it if desired. > > > > > > > > > > > > Having said that, we potentially don't need a dedicated arg if we > > > > > > just make 'migratable=none|preferred|required' be a property of > > > > > > the machine type and hook everything off that > > > > > > > > > > I think my only difficulty with that is that I don't find any of those > > > > > 3 words 'obvious'. > > > > > > > > Any suggestions of replacements for those 3 words? > > > > > > > > Would the descriptions below be enough to clarify their meaning > > > > in documentation? > > > > > > I prefer things that are fairly obvious without needing to look at the > > > documentation until you want the detail. > > > > > > > - NONE: live migration is not needed, and device or machine code > > > > is allowed to enable features that block live migration or > > > > change guest ABI. > > > > (Not implemented yet) > > > > > > > > - PREFERRED: machine and device code should try to make the VM > > > > migratable when possible, but won't emit a warning or error out > > > > if migration is blocked. > > > > (Current default behavior) > > > > > > > > - REQUIRED: live migration support is required, and adding a > > > > migration blocker will be an error. > > > > (Implemented today by --only-migratable) > > > > > > How about > > > -migratable blocked > > > Live migration is not allowed; an outbound migration will fail > > > > "none" and NOT_NEEDED above were about letting QEMU automatically > > enable features that block live migration or change guest ABI. > > > > If that's implied by "blocked", I'd like to get that documented > > explicitly. If that's not implied by "blocked", I don't > > understand what's the use case for "blocked". > > My 'blocked' is stronger - migration is hard disabled by a blocker > always; it's for (rare) cases where the user wants to stop a migration > happening, even if qemu believes it can do it. The main point of my "not_needed" suggestion was to get convenient defaults for use cases where live migration and guest ABI stability is not needed. I don't know yet if that's an implicit feature of your definition of "blocked", or not. > > > > > > > -migratable allowed > > > Live migration is allowed, but some devices/options may block > > > it if they're unable to migrate [current default] > > > > "preferred" above was about QEMU trying to keep live migration > > working as much as possible. That's something we all expect QEMU > > to do, but it's not documented anywhere. > > > > If that's implied by "allowed", I'd like to get that documented > > explicitly. If that's not implied by "allowed", then we have a > > problem. > > My difficulty by your definition is I don't understand what > 'working as much as possible' means - that's the current behaviour > as I understand it. I think mine is more explicit. There's something I don't see documented in your proposal, which I've tried to describe it as "try to keep live migration working as much as possible". I'll try a more detailed description: - Live migration will be possible unless some specific devices or features are enabled. - Devices or features that block live migration won't be enabled by default. - Devices or features that break guest ABI won't be enabled by default. - If an existing configuration allows live migration on a given QEMU version, the same configuration will allow live migration in newer QEMU versions. - If an existing configuration allows live migration with a given machine type version, the same configuration will allow live migration in a newer version of that machine type. If all of the above is implied by "allowed", I'd like to get this documented explicitly. If it's not, we still have a problem. -- Eduardo