netdev - Re: [PATCH net] net/mlx4_en: Force CHECKSUM

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Date:   Wed, 6 Feb 2019 12:15:19 -0800
From:   Saeed Mahameed <saeedm@....mellanox.co.il>
To:     Saeed Mahameed <saeedm@...lanox.com>
Cc:     "edumazet@...gle.com" <edumazet@...gle.com>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [PATCH net] net/mlx4_en: Force CHECKSUM_NONE for short ethernet frames

On Thu, Jan 31, 2019 at 4:06 PM Saeed Mahameed <saeedm@...lanox.com> wrote:
>
> On Thu, 2019-01-31 at 11:42 -0800, Eric Dumazet wrote:
> > On Thu, Jan 31, 2019 at 11:27 AM Saeed Mahameed <saeedm@...lanox.com>
> > wrote:
> > > Are you sure ? you are claiming that the hardware will skip csum
> > > complete i.e cqe->checksum will be 0xffff for padded short IP
> > > frames.
> > > i don't think this is the case, the whole bug is that the hw does
> > > provide a partial cqe->checksum (i.e doesn't included the padding
> > > bytes) even for short eth frames.
> >
> > If the padding is not included, then cqe->checksum is 0xFFFF for
> > correctly received frames.
> >
> > Otherwise, what would be cqe->checksum in this case ? A random value
> > ?
>
> the actual checksum of IP headers+IP payload, while ignoring the
> padding bytes, which is the bug, let me double check..
>
>

Ok, just verified, csum complete (cqe->checksum) is provided and valid
for non-TCP/UDP ip packets, (on specific ConnectX3 HWs)
e.g. ICMP packets or IP fragments go through csum complete,  that
being said, looking at the code before my patch.
when cqe->checksum complete is not valid a IP non-TCP/UDP packet will
report csum NONE, which means my
TODO comment is valid even without my patch :).

We can remove the TODO, although i am fine with it if it kept there,
since it is valid,
but we must add a future optimization task (to tariq's backlog ;)) for
IP non-TCP/UDP traffic to check for
csum unnecessary when csum complete is not an option.

Thanks,
Saeed.