netdev - Re: [RFC PATCH 3/5] bnx2x: Add support for segmentation of tunnels with outer checksums

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Date:   Wed, 24 Aug 2016 08:39:38 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Yuval Mintz <Yuval.Mintz@...gic.com>
Cc:     netdev <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH 3/5] bnx2x: Add support for segmentation of tunnels
 with outer checksums

On Wed, Aug 24, 2016 at 5:33 AM, Yuval Mintz <Yuval.Mintz@...gic.com> wrote:
>> This patch assumes that the bnx2x hardware will ignore existing IPv4/v6 header
>> fields for length and checksum as well as the length and checksum fields for
>> outer UDP and GRE headers.
>>
>> I have no means of testing this as I do not have any bnx2x hardware but thought
>> I would submit it as an RFC to see if anyone out there wants to test this and see
>> if this does in fact enable this functionality allowing us to to segment tunneled
>> frames that have an outer checksum.
>>
>> Signed-off-by: Alexander Duyck <aduyck@...antis.com>
>
> So it took me some [well, a lot] time to reach this, but I've finally  gave it a try.
> I saw a performance boost with the partial support -
> Throughput for vxlan tunnels with and without udpcsum were almost identical
> after this, whereas without this patch the udpcsum prevented GSO and
> a TCP/IPv4 connection on top of it got roughly half the throughput.
>
> However, I did encounter one oddity I couldn't explain -
> After I've disabled tx-udp_tnl-segmentation via ethtool on the base interface,
> got left with:
>    tx-gso-partial: on
>    tx-udp_tnl-segmentation: off
>    tx-udp_tnl-csum-segmentation: on
>
> When I ran traffic over both vxlan tunnels the one with the udpcsum was still
> Passing gso aggregations to base device to transmit [and the throughput was
> same as before], where's the tunnel without the udpcsum showed only
> MTU-sized packets reaching the base interface for transmission [which is what
> I've expected]
>
> Any idea why that happened?

So the way they are implemented tx-udp_tnl-segmentation and
tx-udp_tnl-csum-segmentation are treated as two separate features.
The kernel currently gives them the same treatment as NETIF_F_TSO and
NETIF_F_TSO6.  You can disable one and the other still functions.

Now if you disable tx-gso-partial you should expect to see
tx-udp_tnl-csum-segmentation be disabled because it is dependent on
the partial GSO offload.

- Alex