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Thu, 16 Apr 2026 11:50:31 -0700 (PDT) Received: from x1.local ([142.189.10.167]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8ae6cb9ecbasm41875576d6.30.2026.04.16.11.50.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Apr 2026 11:50:31 -0700 (PDT) Date: Thu, 16 Apr 2026 14:50:29 -0400 From: Peter Xu To: Trieu Huynh Cc: Claudio Fontana , Fabiano Rosas , qemu-devel@nongnu.org, Jim Fehlig , Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Subject: Re: [PATCH 0/2] migration: include timing and RAM stats on destination when query-migrate Message-ID: References: <20260405152612.93027-1-viking4@gmail.com> <878qb05gq7.fsf@suse.de> <5f29c2dd-95eb-44c6-b22e-1909f7453cdf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54, 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_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: qemu development 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 Thu, Apr 16, 2026 at 11:53:55PM +0700, Trieu Huynh wrote: > Hello Peter, Hi, Trieu, > One specific use case where the source is completely unavailable is loading > from a migration snapshot (non-live). > In this scenario, there is no active source QEMU to query_for_stats. The > dst (IMHO) is the only entity that can report how long the loading took > and how much data was actually processed from the snapshot file. > This use case is a little bit niche but still a valid one though, isn't it? Yes it's in general valid, but it also depends. There's a reason that QEMU supported load snapshot over the years and nobody was asking for it. I believe it's because people simply don't need it. Load snapshot, unlike generic form of live migration, doesn't have much uncertainty on its own. It should either succeed after a while, or fail with an error. People should not expect to need to query anything. It will likely, and should, hold true even if with async load snapshot in the future. It is only valid in that it might be useful for developers who works on snapshot, especially tuning the performance. But then it also means we shouldn't expose it to an user API (QMP is in this case). For dev only reportings, we should rely on trace points unless we have good reason to make it visible to users. In general, we don't need to add unnecessary API maint burden to ourselves when not needed. Thanks, -- Peter Xu