net: Implement simple sw TX hashing.

It just xor hashes over IPv4/IPv6 addresses and ports of transport.

The only assumption it makes is that skb_network_header() is set
correctly.

With bug fixes from Eric Dumazet.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 52 insertions, 0 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 7ca9564d2f44..467bfb325123 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -121,6 +121,9 @@
 #include <linux/ctype.h>
 #include <linux/if_arp.h>
 #include <linux/if_vlan.h>
+#include <linux/ip.h>
+#include <linux/ipv6.h>
+#include <linux/in.h>
 
 #include "net-sysfs.h"
 
@@ -1665,6 +1668,53 @@ out_kfree_skb:
  *          --BLG
  */
 
+static u16 simple_tx_hash(struct net_device *dev, struct sk_buff *skb)
+{
+        u32 *addr, *ports, hash, ihl;
+        u8 ip_proto;
+        int alen;
+
+        switch (skb->protocol) {
+        case __constant_htons(ETH_P_IP):
+                ip_proto = ip_hdr(skb)->protocol;
+                addr = &ip_hdr(skb)->saddr;
+                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];
+                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:
+        case IPPROTO_UDP:
+        case IPPROTO_DCCP:
+        case IPPROTO_ESP:
+        case IPPROTO_AH:
+        case IPPROTO_SCTP:
+        case IPPROTO_UDPLITE:
+                hash ^= *ports;
+                break;
+
+        default:
+                break;
+        }
+
+        return hash % dev->real_num_tx_queues;
+}
+
 static struct netdev_queue *dev_pick_tx(struct net_device *dev,
                                         struct sk_buff *skb)
 {
@@ -1672,6 +1722,8 @@ static struct netdev_queue *dev_pick_tx(struct net_device *dev,
 
         if (dev->select_queue)
                 queue_index = dev->select_queue(dev, skb);
+        else if (dev->real_num_tx_queues > 1)
+                queue_index = simple_tx_hash(dev, skb);
 
         skb_set_queue_mapping(skb, queue_index);
         return netdev_get_tx_queue(dev, queue_index);