[RFC] ethdev: introduce entropy calculation

[Andrew Rybchenko]

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 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 :)

I'd avoid usage of term "entropy" in this patch. It is very confusing.