netdev - Re: [PATCH net-next v2] bridge: Synchronize unicast filtering with FDB

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Message-Id: <20160611.155016.671585186295613791.davem@davemloft.net>
Date:	Sat, 11 Jun 2016 15:50:16 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	nikolay@...ulusnetworks.com
Cc:	makita.toshiaki@....ntt.co.jp, stephen@...workplumber.org,
	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
	netdev@....de
Subject: Re: [PATCH net-next v2] bridge: Synchronize unicast filtering with
 FDB

From: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Date: Sat, 11 Jun 2016 18:17:53 +0200

> Oops, I almost missed the v2, sorry about that. So, technically it
> looks correct, but I only fear the scalability impact of the
> change. If there're a large number of vlans adding a macvlan (or any
> device that syncs uc addr) might become very slow and every flag
> change will become very slow too without an option to revert to the
> original behaviour so we'll have to wait for the entries to be added
> in order to delete them.  Another common scenario is having 8021q
> interfaces on top of the bridge with different mac addresses for
> some of the configured vlans (or with macvlans on top of them for
> VRR), that use case would suffer as well because their macs need to
> be local only for those vlans, and not the 2000+ other vlans that
> might exist.  On every sync_uc() call all the fdb entries get
> deleted and added again, so even after deleting some manually they
> can come back unexpectedly after some operation and also the message
> storm from all the deletes and adds could be problematic as well.
> 
> 
> E.g. 2000 br0 vlans, 25 macvlans on br0 (adding them took more than 5 minutes, 53k fdb entries):
> $ bridge fdb del de:8e:9f:16:c5:71 dev br0 vlan 289
> $ ip l set br0 multicast on
> $ bridge fdb | grep 289 | grep de:8e:9f:16:c5:71
> de:8e:9f:16:c5:71 dev br0 vlan 1289 master br0 permanent
> de:8e:9f:16:c5:71 dev br0 vlan 289 master br0 permanent
> 
> In fact you can't escape the slow performance even if you delete all
> entries because on the next flag change or interface add, they will
> be added back.

Yeah, I think the performance implications are too severe too, I'm
not applying this.