netdev - Re: problem with MPLS and TSO/GSO

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Date:	Tue, 9 Aug 2016 21:52:01 -0600
From:	David Ahern <dsa@...ulusnetworks.com>
To:	Lennert Buytenhek <buytenh@...tstofly.org>,
	Roopa Prabhu <roopa@...ulusnetworks.com>,
	Robert Shearman <rshearma@...cade.com>
Cc:	Alexander Duyck <aduyck@...antis.com>, netdev@...r.kernel.org,
	Simon Horman <simon.horman@...ronome.com>
Subject: Re: problem with MPLS and TSO/GSO

On 7/25/16 10:39 AM, Lennert Buytenhek wrote:
> Hi!
> 
> I am seeing pretty horrible TCP transmit performance (anywhere between
> 1 and 10 Mb/s, on a 10 Gb/s interface) when traffic is sent out over a
> route that involves MPLS labeling, and this seems to be due to an
> interaction between MPLS and TSO/GSO that causes all segmentable TCP
> frames that are MPLS-labeled to be dropped on egress.
...
> But, loading mpls_gso doesn't change much -- skb_gso_segment() then
> starts return -EINVAL instead, which is due to the
> skb_network_protocol() call in skb_mac_gso_segment() returning zero.
> And looking at skb_network_protocol(), I don't see how this is
> supposed to work -- skb->protocol is 0 at this point, and there is no
> way to figure out that what we are encapsulating is IP traffic, because
> unlike what is the case with VLAN tags, MPLS labels aren't followed by
> an inner ethertype that says what kind of traffic is in here, you have
> to have explicit knowledge of the payload type for MPLS.
> 
> Any ideas?

A quick update. I have a pretty good handle on the GSO changes for MPLS but I am still puzzled by a few things. Hopefully by end of week I can send out a patch series. Current performance comparison with my changes and a patch from Roopa:

MPLS
====
root@...ny-jessie3:~# ip netns exec ns0 netperf -c -C -H 10.10.10.10 -l 10 -t TCP_STREAM
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.10.10.10 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB

 87380  16384  16384    10.00      3510.26   48.11    48.11    4.491   4.491

non-MPLS
========
root@...ny-jessie3:~# ip netns exec ns0 netperf -c -C -H 172.16.21.22 -l 30 -t TCP_STREAM
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 172.16.21.22 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB

 87380  16384  16384    30.00      9654.97   42.37    42.37    1.438   1.438