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[83.59.163.107]) by smtp.gmail.com with ESMTPSA id df15sm993335edb.24.2021.02.03.08.04.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Feb 2021 08:04:44 -0800 (PST) Subject: Re: ARM Snapshots Not Backwards-Compatible To: "Dr. David Alan Gilbert" , avocado-devel References: <153e5c54-f8bf-d088-502d-502309f5d2a6@redhat.com> <20210203102758.GC2950@work-vm> <20210203104920.GE2950@work-vm> <20210203105933.GF2950@work-vm> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Wed, 3 Feb 2021 17:04:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210203105933.GF2950@work-vm> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.539, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.178, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: Peter Maydell , Andrew Jones , Juan Quintela , QEMU Developers , Aaron Lindsay , qemu-arm Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/3/21 11:59 AM, Dr. David Alan Gilbert wrote: > * Peter Maydell (peter.maydell@linaro.org) wrote: >> On Wed, 3 Feb 2021 at 10:49, Dr. David Alan Gilbert wrote: >>> >>> * Peter Maydell (peter.maydell@linaro.org) wrote: >>>> On Wed, 3 Feb 2021 at 10:28, Dr. David Alan Gilbert wrote: >>>>> >>>>> * Philippe Mathieu-Daudé (philmd@redhat.com) wrote: >>>>>> Cc'ing migration team and qemu-arm@ list. >>>>> >>>>> I'll have to leave the detail of that to the ARM peole; but from a >>>>> migration point of view I think we do want the 64 bit ARM migrations to >>>>> be stable now. Please tie incompatible changes to machine types. >>>> >>>> That is the intention, but because there's no upstream testing >>>> of migration compat, we never notice if we get it wrong. >>>> What is x86 doing to keep cross-version migration working ? >>> >>> I know there used to be some of our team running Avocado tests for >>> compatibility regularly, I'm not sure of the current status. >>> It's something we also do regularly around when we do downstream >>> releases, so we tend to catch them then, although even on x86 that >>> often turns out to be a bit late. >> >> So downstream testing only? > > I thought there used to be some regular avocado testing of upstream but > I'm not sure if it's all architectures and I'm not sure if it's still > happening; I haven't seen any migration issues from it for a while, > which makes me think it isn't. > >> I think that unless we either (a) start >> doing migration-compat testing consistently upstream or (b) RedHat or >> some other downstream start testing and reporting compat issues >> to us for aarch64 as they do for x86-64, in practice we're just >> not going to have working migration compat despite our best >> intentions. (None of the issues Aaron raises were deliberate >> compat breaks -- they're all "we made a change we didn't think >> affected migration but it turns out that it does".) > > I'd agree; we still hit this too often on x86 as well. Cc'ing avocado-devel, since previously discussed: https://www.mail-archive.com/qemu-devel@nongnu.org/msg654139.html