Re: [PATCH 2/2] IB/ipoib: fix GRO merge failure for IPoIB originated TCP streams

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On 2/1/2012 4:07 PM, Eric Dumazet wrote:
If we just turn it into a memcmp with a variable length would
that work for you?

I think yes, FWIW we will compare the IPoIB header, Roland is that okay for you?

A memcmp(xxx, yyy, variable_len) will be out of line and slow, its a bit sad ... Are skb_mac_header(p) / skb_gro_mac_header(skb) going to point to IPoIB header ?

yes, both skb_mac_header(p) / skb_gro_mac_header(skb) point to IPoIB header, however (see next)

Maybe we can keep a fastpath for ethernet case... (the "if (hlen == ETH_HLEN) being always predicted)
Maybe need to introduce gro_hard_header_len as well)

today, IPoIB advertizes hard_header_len which is bigger than the IPoIB header len, this is done such that skbs sent by the network stack have enough headroom for a "pseudoheader" which for few flows (e.g unicast arp replies and multicast) is placed there by the ipoib hard_header function and later used by the xmit function.

So we can either try and change that, such that hard_header_len will be equal to the ipoib header len or add gro_hard_header_len as you suggested, any preferences?



diff --git a/net/core/dev.c b/net/core/dev.c
index 115dee1..62abee4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3500,14 +3500,20 @@ static inline gro_result_t
  __napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
  	struct sk_buff *p;
+	unsigned int hlen = skb->dev->hard_header_len;

  	for (p = napi->gro_list; p; p = p->next) {
  		unsigned long diffs;

  		diffs = (unsigned long)p->dev ^ (unsigned long)skb->dev;
  		diffs |= p->vlan_tci ^ skb->vlan_tci;
-		diffs |= compare_ether_header(skb_mac_header(p),
-					      skb_gro_mac_header(skb));
+		if (hlen == ETH_HLEN)
+			diffs |= compare_ether_header(skb_mac_header(p),
+						      skb_gro_mac_header(skb));
+		else if (!diffs)
+			diffs = memcmp(skb_mac_header(p),
+					skb_gro_mac_header(skb),
+					skb->dev->hard_header_len);
  		NAPI_GRO_CB(p)->same_flow = !diffs;
  		NAPI_GRO_CB(p)->flush = 0;

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