[CentOS] Bonding performance question

[James Pearson]

lhecking at users.sourceforge.net wrote:
>>According to the Linux bonding docs, xmit_hash_policy=layer3+4 uses:
>>
>>   ((source port XOR dest port) XOR
>>          ((source IP XOR dest IP) AND 0xffff)
>>                 modulo slave count
>>
>>So I guess you could plug in in the above IP addresses and port numbers 
>>and see if you get 3 unique results?
> 
>  
>  That's an interesting point - how exactly do you XOR these numbers?
>  Bit by bit? And does 0xffff really mean 0xffffffff in this context?

I guess you need to look at the bonding src code - looks like it is in 
drivers/net/bonding/bond_main.c - for CentOS 5 it is:

/*
  * Hash for the output device based upon layer 3 and layer 4 data. If
  * the packet is a frag or not TCP or UDP, just use layer 3 data.  If it is
  * altogether not IP, mimic bond_xmit_hash_policy_l2()
  */
static int bond_xmit_hash_policy_l34(struct sk_buff *skb,
                                     struct net_device *bond_dev, int count)
{
         struct ethhdr *data = (struct ethhdr *)skb->data;
         struct iphdr *iph = ip_hdr(skb);
         __be16 *layer4hdr = (__be16 *)((u32 *)iph + iph->ihl);
         int layer4_xor = 0;

         if (skb->protocol == htons(ETH_P_IP)) {
                 if (!(iph->frag_off & htons(IP_MF|IP_OFFSET)) &&
                     (iph->protocol == IPPROTO_TCP ||
                      iph->protocol == IPPROTO_UDP)) {
                         layer4_xor = ntohs((*layer4hdr ^ *(layer4hdr + 
1)));
                 }
                 return (layer4_xor ^
                         ((ntohl(iph->saddr ^ iph->daddr)) & 0xffff)) % 
count;

         }

         return (data->h_dest[5] ^ bond_dev->dev_addr[5]) % count;
}

James Pearson