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Wed, 03 Feb 2021 02:53:10 -0800 (PST) MIME-Version: 1.0 References: <153e5c54-f8bf-d088-502d-502309f5d2a6@redhat.com> <20210203102758.GC2950@work-vm> <20210203104920.GE2950@work-vm> In-Reply-To: <20210203104920.GE2950@work-vm> From: Peter Maydell Date: Wed, 3 Feb 2021 10:52:59 +0000 Message-ID: Subject: Re: ARM Snapshots Not Backwards-Compatible To: "Dr. David Alan Gilbert" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::62c; envelope-from=peter.maydell@linaro.org; helo=mail-ej1-x62c.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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: Andrew Jones , Juan Quintela , QEMU Developers , Aaron Lindsay , qemu-arm , =?UTF-8?Q?Philippe_Mathieu=2DDaud=C3=A9?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 3 Feb 2021 at 10:49, Dr. David Alan Gilbert w= rote: > > * Peter Maydell (peter.maydell@linaro.org) wrote: > > On Wed, 3 Feb 2021 at 10:28, Dr. David Alan Gilbert wrote: > > > > > > * Philippe Mathieu-Daud=C3=A9 (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 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".) thanks -- PMM