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From:   Andreas Schwab <schwab@linux-m68k.org>
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Mathieu Malaterre <malat@debian.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Christophe LEROY <christophe.leroy@c-s.fr>,
        Meelis Roos <mroos@linux.ee>, netdev@vger.kernel.org,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH] Revert "net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends"
References: <20180615185645.8921-1-malat@debian.org>
        <fbb95c11-240c-1a11-0a62-0483908c577e@gmail.com>
        <CA+7wUsysaip70ARGQ7Byg1Zktfg0Y1esjEc9HxBGU4sKL8crhg@mail.gmail.com>
        <9d88677a-f2be-2089-79df-15df4e9a5dd6@gmail.com>
Date:   Sun, 17 Jun 2018 12:27:58 +0200
In-Reply-To: <9d88677a-f2be-2089-79df-15df4e9a5dd6@gmail.com> (Eric Dumazet's
        message of "Sat, 16 Jun 2018 05:45:42 -0700")
Message-ID: <m2tvq1672p.fsf@linux-m68k.org>
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On Jun 16 2018, Eric Dumazet <eric.dumazet@gmail.com> wrote:

> I would try something like :
>
> Basically do not bother using CHECKSUM_COMPLETE for small frames that might have been padded.
>
> Since we need to bring one cache line in eth_type_trans() and further header processing,
> computing the checksum in software will be almost free anyway.
>
> diff --git a/drivers/net/ethernet/sun/sungem.c b/drivers/net/ethernet/sun/sungem.c
> index 7a16d40a72d13cf1d522e8a3a396c826fe76f9b9..071039f211a8a33153e888bd4014314ba5e686a4 100644
> --- a/drivers/net/ethernet/sun/sungem.c
> +++ b/drivers/net/ethernet/sun/sungem.c
> @@ -855,9 +855,11 @@ static int gem_rx(struct gem *gp, int work_to_do)
>                         skb = copy_skb;
>                 }
>  
> -               csum = (__force __sum16)htons((status & RXDCTRL_TCPCSUM) ^ 0xffff);
> -               skb->csum = csum_unfold(csum);
> -               skb->ip_summed = CHECKSUM_COMPLETE;
> +               if (len > ETH_ZLEN) {
> +                       csum = (__force __sum16)htons((status & RXDCTRL_TCPCSUM) ^ 0xffff);
> +                       skb->csum = csum_unfold(csum);
> +                       skb->ip_summed = CHECKSUM_COMPLETE;
> +               }
>                 skb->protocol = eth_type_trans(skb, gp->dev);
>  
>                 napi_gro_receive(&gp->napi, skb);

That doesn't change anything.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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