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

[Flavio Leitner]

On Mon, Mar 02, 2020 at 01:11:35PM +0100, Ilya Maximets wrote:
> 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?

I think worth for Ubuntu users to open a bug, so that this gets
solved.

But I think the documentation is still valid. Yi and I spent time
to find the root cause and it is something out of OvS control, so
the best we can do is document the requirement.

Maybe we can word it differently so that the kernel version becomes
less relevant. For example:

"All kernel devices that use the raw socket interface (veth, for example)
require the kernel commit 9d2f67e43b73 ("net/packet: fix packet drop
as of virtio gso") in order to work properly. This commit was merged
in upstream kernel 4.19-rc7, so make sure your kernel is either
newer or contains the backport."

How does that sound to you now?

Thanks,
-- 
fbl