[ovs-dev] [PATCH] userspace-tso: Document the minimum kernel version.

Ilya Maximets i.maximets at ovn.org
Mon Mar 2 12:11:35 UTC 2020

On 2/28/20 11:58 PM, Flavio Leitner wrote:
> The kernel needs to be at least 4.19-rc7 to include the commit
> 9d2f67e43b73 ("net/packet: fix packet drop as of virtio gso")
> otherwise the TSO packets are dropped when using raw sockets.
> Fixes: 29cf9c1b3b9c ("userspace: Add TCP Segmentation Offload support")
> Reported-by: Yi Yang (杨燚)-云服务集团 <yangyi01 at inspur.com>
> Signed-off-by: Flavio Leitner <fbl at sysclose.org>
> ---
>  Documentation/topics/userspace-tso.rst | 4 ++++
>  1 file changed, 4 insertions(+)
> This applies to branch-2.13 as well.
> diff --git a/Documentation/topics/userspace-tso.rst b/Documentation/topics/userspace-tso.rst
> index 0fbac93a5..da370e64f 100644
> --- a/Documentation/topics/userspace-tso.rst
> +++ b/Documentation/topics/userspace-tso.rst
> @@ -113,6 +113,10 @@ __ https://patches.dpdk.org/patch/64136/
>  This fix is expected to be included in the 19.11.1 release. When OVS migrates
>  to this DPDK release, this limitation can be removed.
> +All kernel devices that use the raw socket interface (veth, for example)
> +require a kernel with minimum version of 4.19-rc7 to include the commit:
> +9d2f67e43b73 ("net/packet: fix packet drop as of virtio gso").

I'm not very happy with this kind of documentation updates.  The main reason
is that every distribution uses their own custom kernel with some patches
backported or not.  In this particular case we seem to have issue with
particular ubuntu kernel that happened to not have this bug fix backported.
If someone uses non-lognterm upstream kernel that is out of its support
lifetime it's his/her responsibility to backport bugfixes.
Upstream LTS kernel 4.14 has this bugfix backported and there should be
no issues. Upstream LTS 4.9 might not have this issue at all and work
fine (I didn't check).

What we can document is that particular kernel version from the Ubuntu 16.04
distribution has an issue and should not be used along with userspace-tso.
Ideally, someone should file a bug for ubuntu kernel maintainers, so they
will backport relevant patch and update their kernel since it's still in a
supported state.  In this case we will have no need to document anything.

What do you think?

Best regards, Ilya Maximets.

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