netdev - Re: [PATCH v2 net-next] gro: should aggregate frames without DF

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Date:	Fri, 31 May 2013 22:27:36 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Jerry Chu <hkchu@...gle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH v2 net-next] gro: should aggregate frames without DF

On Fri, 2013-05-31 at 14:18 -0700, Eric Dumazet 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>
> Cc: Ben Hutchings <bhutchings@...arflare.com>
> ---
> v2 : fix from Ben Hutchings (Thanks !)

Reviewed-by: Ben Hutchings <bhutchings@...arflare.com>

>  net/ipv4/af_inet.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index b05ae96..9c090c7 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -1385,7 +1385,7 @@ static struct sk_buff **inet_gro_receive(struct sk_buff **head,
>  		goto out_unlock;
>  
>  	id = ntohl(*(__be32 *)&iph->id);
> -	flush = (u16)((ntohl(*(__be32 *)iph) ^ skb_gro_len(skb)) | (id ^ IP_DF));
> +	flush = (u16)((ntohl(*(__be32 *)iph) ^ skb_gro_len(skb)) | (id & ~IP_DF));
>  	id >>= 16;
>  
>  	for (p = *head; p; p = p->next) {
> @@ -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;
> 
> 

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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