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Commit aa4b9f53 authored by Herbert Xu's avatar Herbert Xu Committed by David S. Miller
Browse files

gro: Optimise Ethernet header comparison 



This patch optimises the Ethernet header comparison to use 2-byte
and 4-byte xors instead of memcmp.  In order to facilitate this,
the actual comparison is now carried out by the callers of the
shared dev_gro_receive function.

This has a significant impact when receiving 1500B packets through
10GbE.

Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4ae5544f

include/linux/etherdevice.h

+21 −0
Original line number Diff line number Diff line
@@ -184,4 +184,25 @@ static inline unsigned compare_ether_addr_64bits(const u8 addr1[6+2], 
}

#endif	/* __KERNEL__ */



/**

 * compare_ether_header - Compare two Ethernet headers

 * @a: Pointer to Ethernet header

 * @b: Pointer to Ethernet header

 *

 * Compare two ethernet headers, returns 0 if equal.

 * This assumes that the network header (i.e., IP header) is 4-byte

 * aligned OR the platform can handle unaligned access.  This is the

 * case for all packets coming into netif_receive_skb or similar

 * entry points.

 */



static inline int compare_ether_header(const void *a, const void *b)

{

	u32 *a32 = (u32 *)((u8 *)a + 2);

	u32 *b32 = (u32 *)((u8 *)b + 2);



	return (*(u16 *)a ^ *(u16 *)b) | (a32[0] ^ b32[0]) |

	       (a32[1] ^ b32[1]) | (a32[2] ^ b32[2]);

}



#endif	/* _LINUX_ETHERDEVICE_H */

include/linux/netdevice.h

+7 −0
Original line number Diff line number Diff line
@@ -1117,6 +1117,13 @@ static inline void skb_gro_reset_offset(struct sk_buff *skb) 
	NAPI_GRO_CB(skb)->data_offset = 0;

}



static inline void *skb_gro_mac_header(struct sk_buff *skb)

{

	return skb_mac_header(skb) < skb->data ? skb_mac_header(skb) :

	       page_address(skb_shinfo(skb)->frags[0].page) +

	       skb_shinfo(skb)->frags[0].page_offset;

}



static inline int dev_hard_header(struct sk_buff *skb, struct net_device *dev,

				  unsigned short type,

				  const void *daddr, const void *saddr,

net/8021q/vlan_core.c

+3 −1
Original line number Diff line number Diff line
@@ -85,7 +85,9 @@ static int vlan_gro_common(struct napi_struct *napi, struct vlan_group *grp, 
		goto drop;



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

		NAPI_GRO_CB(p)->same_flow = p->dev == skb->dev;

		NAPI_GRO_CB(p)->same_flow =

			p->dev == skb->dev && !compare_ether_header(

				skb_mac_header(p), skb_gro_mac_header(skb));

		NAPI_GRO_CB(p)->flush = 0;

	}

net/core/dev.c

+2 −21
Original line number Diff line number Diff line
@@ -215,13 +215,6 @@ static inline struct hlist_head *dev_index_hash(struct net *net, int ifindex) 
	return &net->dev_index_head[ifindex & ((1 << NETDEV_HASHBITS) - 1)];

}



static inline void *skb_gro_mac_header(struct sk_buff *skb)

{

	return skb_mac_header(skb) < skb->data ? skb_mac_header(skb) :

	       page_address(skb_shinfo(skb)->frags[0].page) +

	       skb_shinfo(skb)->frags[0].page_offset;

}



/* Device list insertion */

static int list_netdevice(struct net_device *dev)

{
@@ -2415,29 +2408,16 @@ int dev_gro_receive(struct napi_struct *napi, struct sk_buff *skb) 


	rcu_read_lock();

	list_for_each_entry_rcu(ptype, head, list) {

		struct sk_buff *p;

		void *mac;



		if (ptype->type != type || ptype->dev || !ptype->gro_receive)

			continue;



		skb_set_network_header(skb, skb_gro_offset(skb));

		mac = skb_gro_mac_header(skb);

		mac_len = skb->network_header - skb->mac_header;

		skb->mac_len = mac_len;

		NAPI_GRO_CB(skb)->same_flow = 0;

		NAPI_GRO_CB(skb)->flush = 0;

		NAPI_GRO_CB(skb)->free = 0;



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

			if (!NAPI_GRO_CB(p)->same_flow)

				continue;



			if (p->mac_len != mac_len ||

			    memcmp(skb_mac_header(p), mac, mac_len))

				NAPI_GRO_CB(p)->same_flow = 0;

		}



		pp = ptype->gro_receive(&napi->gro_list, skb);

		break;

	}
@@ -2492,7 +2472,8 @@ static int __napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb) 
	struct sk_buff *p;



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

		NAPI_GRO_CB(p)->same_flow = 1;

		NAPI_GRO_CB(p)->same_flow = !compare_ether_header(

			skb_mac_header(p), skb_gro_mac_header(skb));

		NAPI_GRO_CB(p)->flush = 0;

	}