netdev - Re: [Patch net v3] mlx5: force CHECKSUM

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Date:   Mon, 3 Dec 2018 23:29:49 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [Patch net v3] mlx5: force CHECKSUM_NONE for short ethernet frames

On Mon, Dec 3, 2018 at 11:08 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> The hardware has probably validated the L3 & L4 checksum just fine.
>
> Note that if ip_summed is CHECKSUM_UNNECESSARY, the padding bytes (if any)
> have no impact on the csum that has been verified by the NIC.

Why? Why does the hardware validates L3/L4 checksum when it
supplies a full-packet checksum? What's its point here?

If it really validates L3/L4 checksum, then a full-packet checksum
is not needed.

If a full-packet checksum is supplied, the software is able to use
it to validate L3/L4 checksum, then the hardware doesn't need to
validate it.

I see no reason it provides both at the same time. If it really does,
then all CHECKSUM_COMPLETE code here could be just removed
and would be faster.

Something must be wrong with your argument.

>
> Sorry I do not get your point.

I don't get your point either.

Thanks.