netdev - Re: [net-next PATCH v2 1/9] net: Disable segmentation if checksumming is not supported

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Date:	Sun, 1 May 2016 19:16:12 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Or Gerlitz <gerlitz.or@...il.com>
Cc:	Alexander Duyck <aduyck@...antis.com>,
	"talal@...lanox.com" <talal@...lanox.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Michael Chan <michael.chan@...adcom.com>,
	David Miller <davem@...emloft.net>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eran Ben Elisha <eranbe@...lanox.com>,
	Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [net-next PATCH v2 1/9] net: Disable segmentation if checksumming
 is not supported

On Sun, May 1, 2016 at 1:30 PM, Or Gerlitz <gerlitz.or@...il.com> wrote:
> On Sat, Apr 30, 2016 at 1:43 AM, Alexander Duyck <aduyck@...antis.com> wrote:
>> In the case of the mlx4 and mlx5 driver they do not support IPv6 checksum
>> offload for tunnels.
>
> Alex,
>
> To clarify, when you say "not support IPv6 checksum for tunnels", you
> refer to the offloading of the outer or inner checksum?

In the case of mlx4 it was an issue with both inner and outer due to
IPv6 checksum.  The issue was that the feature was not exposed and yet
the stack was attempting to make use of it in various ways.  The fixes
that resolved the issues are in patches 1 and 4.  If we wanted to we
could move those to net, but then it would be difficult to test the
existing patches on the mlx4 until the net tree containing those
patches was merged back in.

> Still (me and I think also Tariq from our driver team) catching up on
> the series, the primitives and conventions you are introducing using
> and how this applies on mlx5. I saw that Saeed acked the the mlx5e
> patches (7 and 8).

The concept for all this is pretty simple.  What I am doing is
restricting TSO so that we have a fixed size that is used for all
outgoing frames.  Then we precompute the outer headers and use those
values when performing GSO.  By doing this we can populate the UDP
checksum field instead of forcing it to 0 which allows us to perform
TSO for tunnels with outer checksums.

> Specifically, the mlx4 patches are practically fixes so if they don't
> land in 4.7 via net-next we can get them there through net, lets give
> us the few more days needed to catch up from our side.

Actually the mlx4 specific portion of these patches are not really
fixes, they are enabling features.  Specifically IPv6 checksum, TSOv6,
and TSO for VXLAN tunnels with outer checksums.  It is patches 1 and 4
that contain the fix and it likely applies to more than just the mlx4
driver as I believe there is a qlogic driver with a similar feature
flag layout.  If we want we could recommend those patches for stable
and they could probably be back ported into 4.6 after it is released
because I don't see the urgency to push a fix in for something that
has obviously been broken for quite some time now that likely nobody
is ever testing.

- Alex