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Date:	Wed, 18 Jan 2012 16:42:25 +0100
From:	Eric Dumazet <>
To:	Tore Anderson <>
Cc:	netdev <>
Subject: Re: Bugzilla 42595

Le mercredi 18 janvier 2012 à 15:42 +0100, Eric Dumazet a écrit :

> It seems that if you try to have the default ethtool settings (tso, gso,
> tx checksum ... on), transfert is very slow... I am investigating, but I
> suspect that if dst_allfrag() is true, we must disable gso as well.

Following patch is a good compromise, since it disables gso on the
socket on the first frame we consider too big in ip6_fragment().

So the added check on dst_allfrag() is only done once per socket,
instead of adding in sk_can_gso(sk) in fast path.

I can now let gso on on the device, and still have good transfert speed
on sockets hitting the ALLFRAG feature.

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index d97e071..e058747 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -647,8 +647,12 @@ int ip6_fragment(struct sk_buff *skb, int
(*output)(struct sk_buff *))
 	 * or if the skb it not generated by a local socket.
 	if (!skb->local_df && skb->len > mtu) {
+		if (skb->sk && dst_allfrag(skb_dst(skb)))
+			sk_nocaps_add(skb->sk, NETIF_F_GSO_MASK);
 		skb->dev = skb_dst(skb)->dev;
 		icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
 		IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),

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