Re: [PATCH 0/4] Multiple interface support on top of Multi-FD

[Dr. David Alan Gilbert]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Wed, Jun 15, 2022 at 05:43:28PM +0100, Daniel P. Berrangé 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.
> > 
> > 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 [<ip-pair>, 
> > > <multiFD-channels>, <bandwidth_control>]
> > > 
> > >     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.
> 
> Actually I should clarify this is only practical if the two NICs are
> using different IP subnets, otherwise routing rules are not viable.
> So needing to set source IP would be needed to select between a pair
> of NICs on the same IP subnet.

Yeh so I think that's one reason that the idea in this series is OK
(together with the idea for the NUMA stuff) and I suspect there are
other cases as well.

Dave

> Previous usage I've seen has always setup fully distinct IP subnets
> for generic vs storage vs migration network traffic.
> 
> With regards,
> Daniel
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-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK