netdev - Re: [net-next PATCH v3 3/6] udp: Do not pass checksum as a parameter to GSO segmentation

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Message-ID: <CAF=yD-J-+j=OgC_+oz_BT8J4ko2DWTwQikN83j-m9Tzwry-37w@mail.gmail.com>
Date:   Mon, 7 May 2018 14:49:52 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [net-next PATCH v3 3/6] udp: Do not pass checksum as a parameter
 to GSO segmentation

On Mon, May 7, 2018 at 2:08 PM, Alexander Duyck
<alexander.duyck@...il.com> wrote:
> From: Alexander Duyck <alexander.h.duyck@...el.com>
>
> This patch is meant to allow us to avoid having to recompute the checksum
> from scratch and have it passed as a parameter.
>
> Instead of taking that approach we can take advantage of the fact that the
> length that was used to compute the existing checksum is included in the
> UDP header.
>
> Finally to avoid the need to invert the result we can just call csum16_add
> and csum16_sub directly. By doing this we can avoid a number of
> instructions in the loop that is handling segmentation.
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>

Acked-by: Willem de Bruijn <willemb@...gle.com>

Small aside: instead of open-coding the csum16 operations,
it might make sense to define a pseudo_csum_replace2 function
and convert csum_replace2 to call that and only do the inversion.