netdev - Re: [RFC] [PATCH] ip: skip IP checksum for skbs with CHECKSUM

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Message-ID: <20080822183320.1d8fbe34@speedy>
Date:	Fri, 22 Aug 2008 18:33:20 -0400
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Octavian Purdila <opurdila@...acom.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC] [PATCH] ip: skip IP checksum for skbs with
 CHECKSUM_UNNECESSARY set

On Fri, 22 Aug 2008 22:24:31 +0300
Octavian Purdila <opurdila@...acom.com> wrote:

> 
> We are working on a completely in hardware LRO implementation and this patch 
> would simplify the hardware implementation. Is this acceptable?
> 
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
> @@ -415,7 +415,8 @@ int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
>  
>         iph = ip_hdr(skb);
>  
> -       if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
> +       if (!skb_csum_unnecessary(skb) &&
> +           unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
>                 goto inhdr_error;
>  
>         len = ntohs(iph->tot_len);
> 
> --
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The overhead of the additional conditional might outweigh any benefit.
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