From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44153) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fTOBA-0003xo-SC for qemu-devel@nongnu.org; Thu, 14 Jun 2018 05:04:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fTOB9-00032a-Ku for qemu-devel@nongnu.org; Thu, 14 Jun 2018 05:04:28 -0400 References: <1528879723-24675-1-git-send-email-eric.auger@redhat.com> <1528879723-24675-10-git-send-email-eric.auger@redhat.com> <8bf1bccc-b32a-9982-6123-b644c41a96d3@redhat.com> <33a3fa10-bf1a-45cd-73bd-403cbd8d4792@redhat.com> <20180614085954.GM6355@redhat.com> From: Auger Eric Message-ID: Date: Thu, 14 Jun 2018 11:04:16 +0200 MIME-Version: 1.0 In-Reply-To: <20180614085954.GM6355@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 9/9] hw/arm/virt: Add virt-3.0 machine type List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , Laszlo Ersek Cc: eric.auger.pro@gmail.com, qemu-devel@nongnu.org, qemu-arm@nongnu.org, peter.maydell@linaro.org, wei@redhat.com, drjones@redhat.com, ard.biesheuvel@linaro.org, marc.zyngier@arm.com, christoffer.dall@arm.com, zhaoshenglong@huawei.com Hi Dan, Laszlo, On 06/14/2018 10:59 AM, Daniel P. Berrang=C3=A9 wrote: > On Thu, Jun 14, 2018 at 10:56:20AM +0200, Laszlo Ersek wrote: >> Hi Eric, >> >> On 06/14/18 08:27, Auger Eric wrote: >>> Hi Laszlo, >>> >>> On 06/13/2018 11:05 PM, Laszlo Ersek wrote: >>>> On 06/13/18 10:48, Eric Auger wrote: >>>> >>>>> PATCH: merge of ECAM and VCPU extension >>>>> - Laszlo reviewed the ECAM changes but I dropped his R-b >>>>> due to the squash >>>> >>>> Was there any particular reason why the previous patch set (with onl= y >>>> the ECAM enlargement) couldn't be merged first? To be honest I'm not >>>> super happy when my R-b is dropped for non-technical reasons; it see= ms >>>> like wasted work for both of us. >>>> >>>> Obviously if there's a technical dependency or some other reason why >>>> committing the ECAM enlargement in separation would be *wrong*, that= 's >>>> different. Even in that case, wouldn't it be possible to keep the >>>> initial virt-3.0 machtype addition as I reviewed it, and then add th= e >>>> rest in an incremental patch? >>> >>> Sorry about that. My fear was about migration. We would have had 2 vi= rt >>> 3.0 machine models not supporting the same features. While bisecting >>> migration we could have had the source using the high mem ECAM and th= e >>> destination not supporting it. So I preferred to avoid this trouble b= y >>> merging the 2 features in one patch. However I may have kept your R-b >>> restricting its scope to the ECAM stuff. >> >> to my understanding, it is normal to *gradually* add new properties >> during the development cycle, to the new machine type of the upcoming >> QEMU release. To my understanding, it's not expected that migration wo= rk >> between development snapshots built from git. What matters is that two >> official releases, specifying the same machine type, enable the user t= o >> migrate a guest between them (in forward direction). >> >> In every release, so many new features are introduced that it's >> impossible to introduce the new machine type with all the compat knobs >> added at once. Instead, the new machine type is introduced when the >> first feature that requires a compat knob is added to git. All other >> such features extend the compat knobs gradually, during the developmen= t >> cycle. Until the new official release is made (which contains all the >> compat knobs for all the new features), the new machine type simply >> doesn't exist, as far as the public is concerned, so it cannot partake >> in migration either. >> >> This is my understanding anyway. >=20 > That is correct - there is ZERO expectation of migration / ABI stabilit= y > between arbitrary GIT snapshots, only official releases. Prior to the > first release including it, a versioned machine type can be changed > arbitrarily. OK so sufficient consensus on this then. Thanks Eric >=20 > Regards, > Daniel >=20