netdev - Re: [PATCH net-next] gro: should aggregate frames without DF

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Date:	Fri, 31 May 2013 11:14:44 -0700
From:	Jerry Chu <hkchu@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH net-next] gro: should aggregate frames without DF

On Fri, May 31, 2013 at 10:02 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> GRO on IPv4 doesn't aggregate frames if they don't have DF bit set.
>
> Some servers use IP_MTU_DISCOVER/IP_PMTUDISC_PROBE, so linux receivers
> are unable to aggregate this kind of traffic.
>
> The right thing to do is to allow aggregation as long as the DF bit has
> same value on all segments.
>
> bnx2x LRO does this correctly.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Jerry Chu <hkchu@...gle.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> ---
>  net/ipv4/af_inet.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index b05ae96..328cc62 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1384,9 +1384,9 @@ static struct sk_buff **inet_gro_receive(struct sk_buff **head,
>         if (unlikely(ip_fast_csum((u8 *)iph, 5)))
>                 goto out_unlock;
>
> -       id = ntohl(*(__be32 *)&iph->id);
> -       flush = (u16)((ntohl(*(__be32 *)iph) ^ skb_gro_len(skb)) | (id ^ IP_DF));
> -       id >>= 16;
> +       flush = ntohs(iph->tot_len) ^ skb_gro_len(skb);
> +
> +       id = ntohs(iph->id);
>
>         for (p = *head; p; p = p->next) {
>                 struct iphdr *iph2;
> @@ -1407,6 +1407,7 @@ static struct sk_buff **inet_gro_receive(struct sk_buff **head,
>                 NAPI_GRO_CB(p)->flush |=
>                         (iph->ttl ^ iph2->ttl) |
>                         (iph->tos ^ iph2->tos) |
> +                       ((iph->frag_off ^ iph2->frag_off) & htons(IP_DF)) |
>                         ((u16)(ntohs(iph2->id) + NAPI_GRO_CB(p)->count) ^ id);
>
>                 NAPI_GRO_CB(p)->flush |= flush;
>
>

Acked-by: Jerry Chu <hkchu@...gle.com>
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