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([2a01:e0a:280:24f0:9db0:474c:ff43:9f5c]) by smtp.gmail.com with ESMTPSA id a19-20020a0ce353000000b00690314356a4sm1723396qvm.80.2024.03.01.02.41.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Mar 2024 02:41:45 -0800 (PST) Message-ID: Date: Fri, 1 Mar 2024 11:41:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V4 10/14] migration: stop vm for cpr Content-Language: en-US, fr To: Peter Xu , Steven Sistare Cc: qemu-devel@nongnu.org, Fabiano Rosas , "Michael S. Tsirkin" , Jason Wang , Alex Williamson , Gerd Hoffmann , Marc-Andre Lureau , David Hildenbrand References: <1708622920-68779-1-git-send-email-steven.sistare@oracle.com> <1708622920-68779-11-git-send-email-steven.sistare@oracle.com> <9d560585-8f3b-4ad4-82e6-333e8c74b496@oracle.com> From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -6 X-Spam_score: -0.7 X-Spam_bar: / X-Spam_report: (-0.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.096, 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_H2=-0.001, RCVD_IN_SORBS_WEB=1.5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 3/1/24 02:28, Peter Xu wrote: > On Thu, Feb 29, 2024 at 10:21:14AM -0500, Steven Sistare wrote: >> On 2/25/2024 9:08 PM, Peter Xu wrote: >>> On Thu, Feb 22, 2024 at 09:28:36AM -0800, Steve Sistare wrote: >>>> When migration for cpr is initiated, stop the vm and set state >>>> RUN_STATE_FINISH_MIGRATE before ram is saved. This eliminates the >>>> possibility of ram and device state being out of sync, and guarantees >>>> that a guest in the suspended state remains suspended, because qmp_cont >>>> rejects a cont command in the RUN_STATE_FINISH_MIGRATE state. >>>> >>>> Signed-off-by: Steve Sistare >>> >>> Reviewed-by: Peter Xu >>> >>> cpr-reboot mode keeps changing behavior. >>> >>> Could we declare it "experimental" until it's solid? Maybe a patch to >>> document this? >>> >>> Normally IMHO we shouldn't merge a feature if it's not complete, however >>> cpr-reboot is so special that the mode itself is already merged in 8.2 >>> before I started to merge patches, and it keeps changing things. I don't >>> know what else we can do here besides declaring it experimental and not >>> declare it a stable feature. >> >> Hi Peter, the planned/committed functionality for cpr-reboot changed only once, in: >> migration: stop vm for cpr >> >> Suspension to support vfio is an enhancement which adds to the basic functionality, >> it does not change it. This was planned all along, but submitted as a separate > > If VFIO used to migrate without suspension and now it won't, it's a > behavior change? > >> series to manage complexity, as I outlined in my qemu community presentation, >> which I emailed you at the time. >> >> Other "changes" that arose during review were just clarifications and explanations. >> >> So, I don't think cpr-reboot deserves to be condemned to experimental limbo. > > IMHO it's not about a feature being condemned, it's about a kindful > heads-up to the users that one needs to take risk on using it until it > becomes stable, it also makes developers easier because of no limitation on > behavior change. If all the changes are landing, then there's no need for > such a patch. > > If so, please propose the planned complete document patch. I had a feeling > that cpr is still not fully understood by even many developers on the list. > It'll be great that such document will contain all the details one needs to > know on the feature, etc. meaning of the name cpr-reboot (what is "cpr"), > when to use it, how to use it, how it differs from "normal" mode > (etc. lifted limitations on some devices that used to block migration?), > what is enforced (vm stop, suspension, etc.) and what is optionally offered > (VFIO, shared-mem, etc.), the expected behaviors, etc. > > When send it, please copy relevant people (Alex & Cedric for VFIO, while > Markus could also be a good candidate considering the QMP involvement). I second that. If we could have a file under docs/, it would be great. Thanks, C.