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

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

On 2/1/23 14:22, Ori Kam wrote:
> Hi
> 
> Please also see my previous mail.
> 
>> -----Original Message-----
>> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
>> Sent: Wednesday, 1 February 2023 13:11
>>
>> 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. So, good application must use
>> real (always) matching criteria when composing flow rules.
>> 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'm sorry I don't see why.

Will be in reply to Thomas

> 
> This feature is about where to place the rule in the HW.
> This feature can be useful for any HW that as different pipelines for ingress
> and egress traffic. It can be used to save resources or if some actions can be done
> only on one direction then the PMD can allow them and not block the this rule.
> 
> 
>> 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.
>>
> 
> So we agree that the hint is good?

Acceptable since we need to optimize resources.
It would be better without it, but we need it.