Re: [PATCH v7] ethdev: add special flags when creating async transfer table

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 2/1/23 16:48, Thomas Monjalon wrote:
> 01/02/2023 12:38, Andrew Rybchenko:
>> On 2/1/23 14:18, Thomas Monjalon wrote:
>>> 01/02/2023 12:10, Andrew Rybchenko:
>>>> On 2/1/23 13:58, Thomas Monjalon wrote:
>>>>> 01/02/2023 11:17, Andrew Rybchenko:
>>>>>> On 1/18/23 19:18, Thomas Monjalon wrote:
>>>>>>> 18/01/2023 08:28, Andrew Rybchenko:
>>>>>>>> On 11/14/22 14:59, Rongwei Liu wrote:
>>>>>>>>> In case flow rules match only one kind of traffic in a flow table,
>>>>>>>>> then optimization can be done via allocation of this table.
>>>>>>>>> Such optimization is possible only if the application gives a hint
>>>>>>>>> about its usage of the table during initial configuration.
>>>>>>>>>
>>>>>>>>> The transfer domain rules may process traffic from wire or vport,
>>>>>>>>> which may correspond to two kinds of underlayer resources.
>>>>>>>>> That's why the first two hints introduced in this patch are about
>>>>>>>>> wire and vport traffic specialization.
>>>>>>>>> Wire means traffic arrives from the uplink port while vport means
>>>>>>>>> traffic initiated from VF/SF.
>>>>>>>>>
>>>>>>>>> There are two possible approaches for providing the hints.
>>>>>>>>> Using IPv4 as an example:
>>>>>>>>> 1. Use pattern item in both template table and flow rules.
>>>>>>>>>
>>>>>>>>>         pattern_template: pattern ANY_VPORT / eth / ipv4 is 1.1.1.1 / end
>>>>>>>>>         async flow create: pattern ANY_VPORT / eth / ipv4 is 1.1.1.2 / end
>>>>>>>>>
>>>>>>>>>         "ANY_VPORT" needs to be present in each flow rule even if it's
>>>>>>>>>         just a hint. No value to match because matching is already done by
>>>>>>>>>         IPv4 item.
>>>>>>>>>
>>>>>>>>> 2. Add special flags into table_attr.
>>>>>>>>>
>>>>>>>>>         template_table 0 create table_id 0 group 1 transfer vport_orig
>>>>>>>>>
>>>>>>>>> Approach 1 needs to specify the pattern in each flow rule which wastes
>>>>>>>>> memory and is not user friendly.
>>>>>>>>> This patch takes the 2nd approach and introduces one new member
>>>>>>>>> "specialize" into rte_flow_table_attr to indicate possible flow table
>>>>>>>>> optimization.
>>>>>>>>
>>>>>>>> The above description is misleading. It alternates options (1)
>>>>>>>> and (2), but in fact (2) requires (1) as well.
>>>>>>>
>>>>>>> Yes the above description may be misleading
>>>>>>> and it seems you are misleaded :)
>>>>>>
>>>>>> It is not my intention. If it is only my problem, I'm OK to
>>>>>> step back.
>>>>>
>>>>> It's OK to explain and check everything is OK, no worries.
>>>>> Thanks for reviewing.
>>>>>
>>>>>>> I will explain below why the option (2) doesn't require (1).
>>>>>>> I think we should apply the same example to both cases to make it clear:
>>>>>>>
>>>>>>> 1. Use pattern item in both template table and flow rules:
>>>>>>>
>>>>>>>        template table 3 = transfer pattern ANY_VPORT / eth / ipv4 src is 255.255.255.255 / end
>>>>>>>        flow rule = template_table 3 pattern ANY_VPORT / eth / ipv4 src is 1.1.1.1 / end
>>>>>>>
>>>>>>>        The pattern template 3 will be used only to match flows coming from vports.
>>>>>>>        ANY_VPORT needs to be present in each flow rule.
>>>>>>
>>>>>> It looks like I lost something here. Why do we need to specify
>>>>>> it in each flow rule if the matching is already fixed in
>>>>>> template table?
>>>>>
>>>>> I think that's how template tables are designed.
>>>>> Ori, please could you point us to the relevant documentation?
>>>>>
>>>>>>>        ANY_VPORT matching is redundant with IP src 1.1.1.1 because
>>>>>>>        the user knows 1.1.1.1 is the IP of a vport.
>>>>>>
>>>>>> What should happen if a packet with src IP 1.1.1.1 comes from
>>>>>> the wire? Almost anything could come from network.
>>>>>
>>>>> It a packet comes from a wired port AND
>>>>> the PMD did an optimization based on this hint,
>>>>> then the packet could be not matched.
>>>>
>>>> So, the hint changes matching results and therefore becomes
>>>> a strange (extra) matching criteria under specific
>>>> circumstance. It sounds bad.
>>>
>>> In this case, the user made a wrong assumption.
>>> If the user does not do a mistake, the behavior should be the same
>>> whether the hint is used or ignored.
>>>
>>>> So, good application must use
>>>> real (always) matching criteria when composing flow rules.
>>>
>>> Of course, nothing replaces matching criteria.
>>>
>>>> So, RTE flow API should provide a way to write a good
>>>> application without extra pain.
>>>> That's why I'm saying that (2) requires (1) anyway.
>>>
>>> I don't follow this sentence.
>>> If you mean with hint, flow matching is still required, then yes,
>>> this is what I emphasized in my rewrite of the case (2) below.
>>>
>>>> It does not say that hint is not required at all.
>>>> It is still useful for resources usage optimization if
>>>> application knows how it is going to use particular table.
>>>
>>> Yes, that's an optional optimization.
>>> It should not change the rules,
>>> and it should not change the functional behavior
>>> if the user does not do mistakes.
>>
>> So, we basically agree on the topic, but my goal here is a bit
>> bigger. Make it easier for a user to avoid mistakes. May be it
>> is stupid goal :) and all efforts are vain.
>> If we have a match item with similar functionality it would be
>> easy to just put it into a pattern. Otherwise, it could be
>> complicated, have high chances to be skipped and rely on
>> implicit matching criteria imposed by the hint on the HW
>> which takes it into account.
> 
> We may highlight in the doc that the functional behaviour must not rely
> on the hints. It is only optional optimization and effects may vary
> with differents driver.
> What do you think? I don't know what else to do about user mistakes :)

As I said - add corresponding pattern items.
Anyway, hint itself is OK and makes sense. Hopefully
documentation highlights that pattern match is required.
If so,

Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>