> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen at networkplumber.org]
> Sent: Thursday, June 5, 2014 4:16 PM
> To: Doherty, Declan
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2 1/4] Link Bonding Library
>
> On Wed, 4 Jun 2014 16:18:02 +0100
> declan.doherty at intel.com wrote:
>
> > From: Declan Doherty <declan.doherty at intel.com>
> >
> > - Broadcast TX burst broadcast bug fix
> > - Add/remove slave behavior fix
> > - Checkpatch fixes
> >
> > Signed-off-by: Declan Doherty <declan.doherty at intel.com>
>
> There are some pretty weak hash functions in there.
>
> What about using:
> .....
Hi Stephen,
I suppose the naming of these as hash functions is probably misleading, the aim
is not to create a unique hash for each flow with minimal collisions but to
help balance traffic flows across the slaves of the bonded device, and as we
are doing a modulus calculation based on the number of slaves attached, which I
believe will typically be in the 2-4 range, I'm not sure that a stronger
hashing function will give a better balance of flows across the slaves. For
example in the Linux kernel implementation of the link bonding driver the mac
hashing only uses the last byte of src & dst mac addresses to calculate it's
eth hash.
/* L2 hash helper */
static inline u32 bond_eth_hash(struct sk_buff *skb)
{
struct ethhdr *data = (struct ethhdr *)skb->data;
if (skb_headlen(skb) >= offsetof(struct ethhdr, h_proto))
return data->h_dest[5] ^ data->h_source[5];
return 0;
}
I'll investigate and see if a stronger hashing function will result in a better
balancing of flows.
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