[PATCH] net: Check skb->rxhash in gro_receive

[Tom Herbert <therbert@google.com>]

When initializing a gro_list for a packet, first check the rxhash of
the incoming skb against that of the skb's in the list. This should be
a very strong inidicator of whether the flow is going to be matched,
and potentially allows a lot of other checks to be short circuited.

Signed-off-by: Tom Herbert <therbert@google.com>
---
 net/core/dev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index ce01847..88bf426 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3794,10 +3794,14 @@ static void gro_list_prepare(struct napi_struct *napi, struct sk_buff *skb)
 {
 	struct sk_buff *p;
 	unsigned int maclen = skb->dev->hard_header_len;
+	u32 hash = skb_get_hash(skb);
 
 	for (p = napi->gro_list; p; p = p->next) {
 		unsigned long diffs;
 
+		if ((diffs = (hash != p->rxhash)))
+			goto skip;
+
 		diffs = (unsigned long)p->dev ^ (unsigned long)skb->dev;
 		diffs |= p->vlan_tci ^ skb->vlan_tci;
 		if (maclen == ETH_HLEN)
@@ -3807,6 +3811,7 @@ static void gro_list_prepare(struct napi_struct *napi, struct sk_buff *skb)
 			diffs = memcmp(skb_mac_header(p),
 				       skb_gro_mac_header(skb),
 				       maclen);
+skip:
 		NAPI_GRO_CB(p)->same_flow = !diffs;
 		NAPI_GRO_CB(p)->flush = 0;
 	}
-- 
1.8.5.1