net: Improve simple_tx_hash().
Based upon feedback from Eric Dumazet and Andi Kleen.
Cure several deficiencies in simple_tx_hash() by using
jhash + reciprocol multiply.
1) Eliminates expensive modulus operation.
2) Makes hash less attackable by using random seed.
3) Eliminates endianness hash distribution issues.
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/dev.c b/net/core/dev.c
index 2eed17b..7e2d5274 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -124,6 +124,8 @@
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/in.h>
+#include <linux/jhash.h>
+#include <linux/random.h>
#include "net-sysfs.h"
@@ -1668,34 +1670,37 @@
* --BLG
*/
+static u32 simple_tx_hashrnd;
+static int simple_tx_hashrnd_initialized = 0;
+
static u16 simple_tx_hash(struct net_device *dev, struct sk_buff *skb)
{
- u32 *addr, *ports, hash, ihl;
+ u32 addr1, addr2, ports;
+ u32 hash, ihl;
u8 ip_proto;
- int alen;
+
+ if (unlikely(!simple_tx_hashrnd_initialized)) {
+ get_random_bytes(&simple_tx_hashrnd, 4);
+ simple_tx_hashrnd_initialized = 1;
+ }
switch (skb->protocol) {
case __constant_htons(ETH_P_IP):
ip_proto = ip_hdr(skb)->protocol;
- addr = &ip_hdr(skb)->saddr;
+ addr1 = ip_hdr(skb)->saddr;
+ addr2 = ip_hdr(skb)->daddr;
ihl = ip_hdr(skb)->ihl;
- alen = 2;
break;
case __constant_htons(ETH_P_IPV6):
ip_proto = ipv6_hdr(skb)->nexthdr;
- addr = &ipv6_hdr(skb)->saddr.s6_addr32[0];
+ addr1 = ipv6_hdr(skb)->saddr.s6_addr32[3];
+ addr2 = ipv6_hdr(skb)->daddr.s6_addr32[3];
ihl = (40 >> 2);
- alen = 8;
break;
default:
return 0;
}
- ports = (u32 *) (skb_network_header(skb) + (ihl * 4));
-
- hash = 0;
- while (alen--)
- hash ^= *addr++;
switch (ip_proto) {
case IPPROTO_TCP:
@@ -1705,14 +1710,17 @@
case IPPROTO_AH:
case IPPROTO_SCTP:
case IPPROTO_UDPLITE:
- hash ^= *ports;
+ ports = *((u32 *) (skb_network_header(skb) + (ihl * 4)));
break;
default:
+ ports = 0;
break;
}
- return hash % dev->real_num_tx_queues;
+ hash = jhash_3words(addr1, addr2, ports, simple_tx_hashrnd);
+
+ return (u16) (((u64) hash * dev->real_num_tx_queues) >> 32);
}
static struct netdev_queue *dev_pick_tx(struct net_device *dev,