netdev - Re: [PATCH] sky2: don't do GRO on second port

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Date:	Thu, 02 Sep 2010 12:41:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	David Miller <davem@...emloft.net>, shemminger@...tta.com,
	herbert@...dor.apana.org.au, netdev@...r.kernel.org
Subject: Re: [PATCH] sky2: don't do GRO on second port

Le jeudi 02 septembre 2010 à 09:55 +0000, Jarek Poplawski a écrit :

> 
> Exactly, but there is no "a single napi --> device mapping". And sky2
> uses the same model. So, there is only a question of cost of this test,
> and a question of probability of gro errors on collisions without such
> a test in normal use. (And if gro can never do such errors for other
> reasons?)

Two vlans might carry packets in different domains, with a clash of IP
space and TCP flows. Even with a probability of 0.000000001%, we cannot
ever merge two packets of different domains. Really !

napi->dev is not used in GRO path, as mentioned earlier,
but in napi_get_frags(), while not needed.

To make this very clear, I suggest following patch :

[PATCH net-next-2.6] gro: remove use of napi->dev

Only use of napi->dev in GRO stack is the one found in napi_get_frags()

We can remove it and use a plain dev_alloc_skb() call.

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 net/core/dev.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index d8c43e7..607057a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3248,9 +3248,11 @@ struct sk_buff *napi_get_frags(struct napi_struct *napi)
 	struct sk_buff *skb = napi->skb;
 
 	if (!skb) {
-		skb = netdev_alloc_skb_ip_align(napi->dev, GRO_MAX_HEAD);
-		if (skb)
+		skb = dev_alloc_skb(GRO_MAX_HEAD + NET_IP_ALIGN);
+		if (skb) {
+			skb_reserve(skb, NET_IP_ALIGN);
 			napi->skb = skb;
+		}
 	}
 	return skb;
 }


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