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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id h16-20020ac846d0000000b0040ff387de83sm4502892qto.45.2023.09.05.09.46.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Sep 2023 09:46:06 -0700 (PDT) Date: Tue, 5 Sep 2023 12:46:03 -0400 From: Peter Xu To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: "Wang, Lei" , qemu-devel@nongnu.org, Zhiyi Guo , Markus Armbruster , Leonardo Bras Soares Passos , Fabiano Rosas , Juan Quintela , Eric Blake , Chensheng Dong , Joao Martins Subject: Re: [PATCH for-8.2 v2 2/2] migration: Allow user to specify migration switchover bandwidth Message-ID: References: <20230803155344.11450-1-peterx@redhat.com> <20230803155344.11450-3-peterx@redhat.com> <8bb36b56-e2f6-ece8-0d8f-90b87a3b5c40@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: 2.1.29 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 Fri, Sep 01, 2023 at 09:37:32AM +0100, Daniel P. Berrangé wrote: > > > When the user wants to have migration only use 5Gbps out of that 10Gbps, > > > one can set max-bandwidth to 5Gbps, along with max-switchover-bandwidth to > > > 5Gbps so it'll never use over 5Gbps too (so the user can have the rest > > > > Hi Peter. I'm curious if we specify max-switchover-bandwidth to 5Gbps over a > > 10Gbps network, in the completion stage will it send the remaining data in 5Gbps > > using downtime_limit time or in 10Gbps (saturate the network) using the > > downtime_limit / 2 time? Seems this parameter won't rate limit the final stage:) > > Effectively the mgmt app is telling QEMU to assume that this > much bandwidth is available for use during switchover. If QEMU > determines that, given this available bandwidth, the remaining > data can be sent over the link within the downtime limit, it > will perform the switchover. When sending this sitchover data, > it will actually transmit the data at full line rate IIUC. I'm right at reposting this patch, but then I found that the max-available-bandwidth is indeed confusing (as Lei's question shows). We do have all the bandwidth throttling values in the pattern of max-*-bandwidth and this one will start to be the outlier that it won't really throttle the network. If the old name "available-bandwidth" is too general, I'm now considering "avail-switchover-bandwidth" just to leave max- out of the name to differenciate, if some day we want to add a real throttle for switchover we can still have a sane name. Any objections before I repost? Thanks, -- Peter Xu