[RFC] ethdev: introduce entropy calculation

[Thomas Monjalon]

15/12/2023 14:44, Ferruh Yigit:
> On 12/14/2023 5:26 PM, Stephen Hemminger wrote:
> > On Thu, 14 Dec 2023 17:18:25 +0000
> > Ori Kam <orika at nvidia.com> wrote:
> > 
> >>>> Since encap groups number of different 5 tuples together, if HW doesn’t know
> >>>> how to RSS
> >>>> based on the inner application will not be able to get any distribution of  
> >>> packets.  
> >>>>
> >>>> This value is used to reflect the inner packet on the outer header, so  
> >>> distribution  
> >>>> will be possible.
> >>>>
> >>>> The main use case is, if application does full offload and implements the encap  
> >>> on  
> >>>> the RX.
> >>>> For example:
> >>>> Ingress/FDB  match on 5 tuple encap send to hairpin / different port in case of
> >>>> switch.
> >>>>  
> >>>
> >>> Smart idea! So basically the user is able to get an idea on how good the RSS
> >>> distribution is, correct?
> >>>   
> >>
> >> Not exactly, this simply allows the distribution.
> >> Maybe entropy is a bad name, this is the name they use in the protocol, but in reality
> >> this is some hash calculated on the packet header before the encap and set in the encap header.
> >> Using this hash results in entropy for the packets. Which can be used for load balancing.
> >>
> >> Maybe better name would be:
> >> Rte_flow_calc_entropy_hash?
> >>
> >> or maybe rte_flow_calc_encap_hash (I like it less since it looks like we calculate the hash on the encap data and not the inner part)
> >>
> >> what do you think?
> > 
> > Entropy has meaning in crypto and random numbers generators that is different from
> > this usage. So entropy is bad name to use. Maybe rte_flow_hash_distribution?
> >
> 
> Hi Ori,
> 
> Thank you for the description, it is more clear now.
> 
> And unless this is specifically defined as 'entropy' in spec, I am too
> for rename.
> 
> At least in VXLAN spec, it is mentioned that this field is to "enable a
> level of entropy", but not exactly names it as entropy.

Exactly my thought about the naming.
Good to see I am not alone thinking this naming is disturbing :)