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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id j19-20020a05600c1c1300b0039c5645c60fsm8575473wms.3.2022.06.15.12.14.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jun 2022 12:14:28 -0700 (PDT) Date: Wed, 15 Jun 2022 20:14:26 +0100 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: "manish.mishra" , Het Gala , qemu-devel@nongnu.org, quintela@redhat.com, pbonzini@redhat.com, armbru@redhat.com, eblake@redhat.com Subject: Re: [PATCH 0/4] Multiple interface support on top of Multi-FD Message-ID: References: <20220609073305.142515-1-het.gala@nutanix.com> <7209116d-ef87-ee6f-5126-e23b55121f49@nutanix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.5 (2022-05-16) Received-SPF: pass client-ip=170.10.129.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, 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, T_SCC_BODY_TEXT_LINE=-0.01 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" * Daniel P. Berrangé (berrange@redhat.com) wrote: > On Fri, Jun 10, 2022 at 05:58:31PM +0530, manish.mishra wrote: > > > > On 09/06/22 9:17 pm, Daniel P. Berrangé wrote: > > > On Thu, Jun 09, 2022 at 07:33:01AM +0000, Het Gala wrote: > > > > As of now, the multi-FD feature supports connection over the default network > > > > only. This Patchset series is a Qemu side implementation of providing multiple > > > > interfaces support for multi-FD. This enables us to fully utilize dedicated or > > > > multiple NICs in case bonding of NICs is not possible. > > > > > > > > > > > > Introduction > > > > ------------- > > > > Multi-FD Qemu implementation currently supports connection only on the default > > > > network. This forbids us from advantages like: > > > > - Separating VM live migration traffic from the default network. > > > > Hi Daniel, > > > > I totally understand your concern around this approach increasing compexity inside qemu, > > > > when similar things can be done with NIC teaming. But we thought this approach provides > > > > much more flexibility to user in few cases like. > > > > 1. We checked our customer data, almost all of the host had multiple NIC, but LACP support > > > >     in their setups was very rare. So for those cases this approach can help in utilise multiple > > > >     NICs as teaming is not possible there. > > AFAIK, LACP is not required in order to do link aggregation with Linux. > Traditional Linux bonding has no special NIC hardware or switch requirements, > so LACP is merely a "nice to have" in order to simplify some aspects. > > IOW, migration with traffic spread across multiple NICs is already > possible AFAICT. Are we sure that works with multifd? I've seen a lot of bonding NIC setups which spread based on a hash of source/destination IP and port numbers; given that we use the same dest port and IP at the moment what happens in reality? That hashing can be quite delicate for high bandwidth single streams. > I can understand that some people may not have actually configured > bonding on their hosts, but it is not unreasonable to request that > they do so, if they want to take advantage fo aggrated bandwidth. > > It has the further benefit that it will be fault tolerant. With > this proposal if any single NIC has a problem, the whole migration > will get stuck. With kernel level bonding, if any single NIC haus > a problem, it'll get offlined by the kernel and migration will > continue to work across remaining active NICs. > > > 2. We have seen requests recently to separate out traffic of storage, VM netwrok, migration > > > >     over different vswitch which can be backed by 1 or more NICs as this give better > > > >     predictability and assurance. So host with multiple ips/vswitches can be very common > > > >     environment. In this kind of enviroment this approach gives per vm or migration level > > > >     flexibilty, like for critical VM we can still use bandwidth from all available vswitch/interface > > > >     but for normal VM they can keep live migration only on dedicated NICs without changing > > > >     complete host network topology. > > > >     At final we want it to be something like this [, , ] > > > >     to provide bandwidth_control per interface. > > Again, it is already possible to separate migration traffic from storage > traffic, from other network traffic. The target IP given will influence > which NIC is used based on routing table and I know this is already > done widely with OpenStack deployments. > > > 3. Dedicated NIC we mentioned as a use case, agree with you it can be done without this > > > >     approach too. > > > > > > Multi-interface with Multi-FD > > > > ----------------------------- > > > > Multiple-interface support over basic multi-FD has been implemented in the > > > > patches. Advantages of this implementation are: > > > > - Able to separate live migration traffic from default network interface by > > > > creating multiFD channels on ip addresses of multiple non-default interfaces. > > > > - Can optimize the number of multi-FD channels on a particular interface > > > > depending upon the network bandwidth limit on a particular interface. > > > Manually assigning individual channels to different NICs is a pretty > > > inefficient way to optimizing traffic. Feels like you could easily get > > > into a situation where one NIC ends up idle while the other is busy, > > > especially if the traffic patterns are different. For example with > > > post-copy there's an extra channel for OOB async page requests, and > > > its far from clear that manually picking NICs per chanel upfront is > > > going work for that. The kernel can continually dynamically balance > > > load on the fly and so do much better than any static mapping QEMU > > > tries to apply, especially if there are multiple distinct QEMU's > > > competing for bandwidth. > > > > > Yes, Daniel current solution is only for pre-copy. As with postcopy > > multiFD is not yet supported but in future we can extend it for postcopy I had been thinking about explicit selection of network device for NUMA use though; ideally I'd like to be able to associate a set of multifd threads to each NUMA node, and then associate a NIC with that set of threads; so that the migration happens down the NIC that's on the node the RAM is on. On a really good day you'd have one NIC per top level NUMA node. > > channels too. > > > > > > Implementation > > > > -------------- > > > > > > > > Earlier the 'migrate' qmp command: > > > > { "execute": "migrate", "arguments": { "uri": "tcp:0:4446" } } > > > > > > > > Modified qmp command: > > > > { "execute": "migrate", > > > > "arguments": { "uri": "tcp:0:4446", "multi-fd-uri-list": [ { > > > > "source-uri": "tcp::6900", "destination-uri": "tcp:0:4480", > > > > "multifd-channels": 4}, { "source-uri": "tcp:10.0.0.0: ", > > > > "destination-uri": "tcp:11.0.0.0:7789", > > > > "multifd-channels": 5} ] } } > > > > ------------------------------------------------------------------------------ > > > > > > > > Earlier the 'migrate-incoming' qmp command: > > > > { "execute": "migrate-incoming", "arguments": { "uri": "tcp::4446" } } > > > > > > > > Modified 'migrate-incoming' qmp command: > > > > { "execute": "migrate-incoming", > > > > "arguments": {"uri": "tcp::6789", > > > > "multi-fd-uri-list" : [ {"destination-uri" : "tcp::6900", > > > > "multifd-channels": 4}, {"destination-uri" : "tcp:11.0.0.0:7789", > > > > "multifd-channels": 5} ] } } > > > > ------------------------------------------------------------------------------ > > > These examples pretty nicely illustrate my concern with this > > > proposal. It is making QEMU configuration of migration > > > massively more complicated, while duplicating functionality > > > the kernel can provide via NIC teaming, but without having > > > ability to balance it on the fly as the kernel would. > > > > Yes, agree Daniel this raises complexity but we will make sure that it does not > > > > change/imapct anything existing and we provide new options as optional. > > The added code is certainly going to impact ongoing maint of QEMU I/O > layer and migration in particular. I'm not convinced this complexity > is compelling enough compared to leveraging kernel native bonding > to justify the maint burden it will impose. Dave > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK