linux-kernel - Re: [PATCH] Revert "net: pskb_trim_rcsum() and CHECKSUM

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Date:   Sun, 17 Jun 2018 12:27:58 +0200
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Mathieu Malaterre <malat@...ian.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Christophe LEROY <christophe.leroy@....fr>,
        Meelis Roos <mroos@...ux.ee>, netdev@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] Revert "net: pskb_trim_rcsum() and CHECKSUM_COMPLETE are friends"

On Jun 16 2018, Eric Dumazet <eric.dumazet@...il.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@...ux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
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