netdev - Re: [Patch net v2] mlx5: fixup checksum for short ethernet frame padding

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Date:   Fri, 18 Jan 2019 16:45:30 -0800
From:   Saeed Mahameed <saeedm@....mellanox.co.il>
To:     Christoph Paasch <christoph.paasch@...il.com>
Cc:     Nikola Ciprich <nikola.ciprich@...uxbox.cz>,
        Saeed Mahameed <saeedm@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>
Subject: Re: [Patch net v2] mlx5: fixup checksum for short ethernet frame padding

On Thu, Jan 17, 2019 at 5:19 PM Christoph Paasch
<christoph.paasch@...il.com> wrote:
>
> Hello,
>
> On Sun, Jan 6, 2019 at 3:12 AM Saeed Mahameed <saeedm@....mellanox.co.il> wrote:
> >
> > On Sat, Jan 5, 2019 at 8:35 PM Nikola Ciprich
> > <nikola.ciprich@...uxbox.cz> wrote:
> > >
> > > Hi Saeed,
> > >
> > >
> > > > Most likely the same issue, we are finalizing the patch initially
> > > > proposed by Cong, you can find it here, I plan to submit it next week,
> > > > after all the regression tests.
> > > >
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/saeed/linux.git/commit/?h=topic/csum-fix
> > > >
> > > > It would be nice if you verify this fixes your issue.
> > >
> > > I tried 4.20.0 + this fix and the problems are gone! haven't done backport to 4.19 yet.
> > >
> > > cheers!
> >
> > Thanks nik for your input, we will submit a similar fix very soon.
>
> We are also seeing similar issues on v4.14.94, as Eric's patch got
> backported with 6bf32cda46eb.
>
> I backported (had to do some changes to solve the conflicts) your fix
> from topic/csum-fix to v4.14.94, but then I still get the warning when
> the frame is bigger than ETH_ZLEN (which is quite unsurprising ;-)).

Hi Christoph,
This is a bummer, we only saw the issue with switches that are padding
packets up to ETH_ZLEN,
and they never touch packets larger than this size, still i agree that
the issue could happen with any
packet size, we just never saw such hardware/switch which produces
packets with non-zero end padding!

the only option i can suggest is to disable checksum complete, it can
be done via a priv-flag which was submitted
to kernel v4.20.

commit b856df28f9230a47669efbdd57896084caadb2b3
Author: Or Gerlitz <ogerlitz@...lanox.com>
Date:   Sun Jul 1 08:58:38 2018 +0000

    net/mlx5e: Allow reporting of checksum unnecessary

    Currently we practically never report checksum unnecessary, because
    for all IP packets we take the checksum complete path.

    Enable non-default runs with reprorting checksum unnecessary, using
    an ethtool private flag. This can be useful for performance evals
    and other explorations.

    Signed-off-by: Or Gerlitz <ogerlitz@...lanox.com>
    Reviewed-by: Tariq Toukan <tariqt@...lanox.com>
    Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>



> Eric already pointed that out that one can cook bigger frames with
> padding (cfr., https://patchwork.ozlabs.org/patch/1004117/).
>
> What is the plan to get rid of the warning in v4.14-stable?
>
>
> Thanks,
> Christoph
>
>
>
> >
> > >
> > > nik
> > >
> > >
> > >
> > > >
> > > > Thanks,
> > > > Saeed.
> > > >
> > > >
> > > > > thanks a lot in advance
> > > > >
> > > > > BR
> > > > >
> > > > > nik
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > >
> > > > > > Thanks,
> > > > > > Saeed.
> > > > > >
> > > >
> > >
> > > --
> > > -------------------------------------
> > > Ing. Nikola CIPRICH
> > > LinuxBox.cz, s.r.o.
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