RE: [RFC] ethdev: introduce entropy calculation

[Ori Kam <orika@nvidia.com>]

Hi Andrew, Stephen, Ferruh and Thomas,

> -----Original Message-----
> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> Sent: Saturday, December 16, 2023 11:04 AM
> 
> On 12/15/23 19:21, Thomas Monjalon wrote:
> > 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@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 :)
> 
> I'd avoid usage of term "entropy" in this patch. It is very confusing.

What about rte_flow_calc_encap_hash?