netdev - Re: [PATCH 2/2] net: ip, ipv6: handle gso skbs in forwarding path

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Date:	Sun, 26 Jan 2014 10:22:28 +0100
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] net: ip, ipv6: handle gso skbs in forwarding path

Eric Dumazet <eric.dumazet@...il.com> wrote:
> > +static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)
> > +{
> > +	unsigned len;
> > +
> > +	if (skb->local_df)
> > +		return false;
> > +	len = skb_is_gso(skb) ? skb_gso_network_seglen(skb) : skb->len;
> > +
> > +	return len > mtu;
> 
> The function should avoid extra computation/tests for small packets.
> 
> if (skb->len <= mtu || skb->local_df)
> 	return false;

Good idea!  Will change it as per your suggestion.

> if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu)
> 	return false;
> 
> return true;
> 
> > +}
> > +
> > +/* called if GSO skb needs to be fragmented on forward.  */
> > +static int ip_forward_finish_gso(struct sk_buff *skb)
> > +{
> > +	struct sk_buff *segs = skb_gso_segment(skb, 0);
> 
> 0 is very pessimistic.
> 
> Have you tried :
> 
> netdev_features_t features = netif_skb_features(skb); 
> struct sk_buff *segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);

No.  I'll see if this works for me, then include it in V2.

Thanks Eric.
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