[dpdk-dev] [PATCH v2 1/4] Link Bonding Library

Stephen Hemminger stephen at networkplumber.org
Fri Jun 6 17:13:30 CEST 2014


On Fri, 6 Jun 2014 09:07:23 +0000
"Doherty, Declan" <declan.doherty at intel.com> wrote:

> > -----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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> 

The ether hash is very quick using multplicative hash on 64 bit value.


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