netdev - Re: VLAN performance issues with Open vSwitch when 8021q not loaded

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Date:   Fri, 18 May 2018 08:12:20 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Mikhail Sennikovsky <mikhail.sennikovskii@...fitbricks.com>,
        netdev@...r.kernel.org
Subject: Re: VLAN performance issues with Open vSwitch when 8021q not loaded



On 05/18/2018 06:24 AM, Mikhail Sennikovsky wrote:
> Hi all,
> 
> We were recently experiencing network performance issues with VLAN
> networking setup with Open vSwitch, for the ingress traffic coming to
> VLAN trunk port of the ovs.
> As we discovered, the issue was caused by gro not working for it,
> which in turn was because the gro receive callbacks for 802.1Q payload
> type are defined in the 8021q module (see
> https://elixir.bootlin.com/linux/v4.16.9/source/net/8021q/vlan.c#L762
> ), which was not loaded.
> This resulted in a significant bandwidth performance drop, having
> ~3Gbps instead of the expected ~7Gbps for a simple iperf3 test in our
> case.
> 
> The obvious work-around would be to load the 8021q module, which
> indeed makes bandwidth performance back to the expected numbers.
> This seems like a hidden and not obvious magic however.
> 
> So I'm questioning, whether it makes sense to have the gro receive
> callbacks for 802.1Q and 802.1ad moved to some common place, that
> would be used/enabled by both 8021q and openvswitch modules.


Sure, GRO should do whatever it can.

TCP IPv6 traffic can be aggregated by GRO even if IPv6 module is not loaded.

net/ipv6/Makefile :

ipv6-offload := ip6_offload.o tcpv6_offload.o exthdrs_offload.o
...
obj-$(CONFIG_INET) += output_core.o protocol.o $(ipv6-offload)