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

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

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.

> 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?

>     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.

> 
> 2. Add specialization flag into template table attribute:
> 
>     template table 3 = transfer VPORT_ORIG pattern eth / ipv4 src is 255.255.255.255 / end
>     flow rule = template_table 3 pattern eth / ipv4 src is 1.1.1.1 / end
> 
>     The pattern template 3 can be used only to match flows coming from vports.

In this case it is interesting how it will behave on:
a NIC which does not support VPORT_ORIG and just ignores it
VS
a NIC which support VPORT_ORIG and takes it into account.

> 
>> (2) is simply done on different level - much earlier, before
>> flow rules creation. Since resources allocation is assumed to
>> be done on table creation, we need to know the purpose of the
>> table in advance to optimize resources allocation.
> 
> Actually in both cases we get the hint at template table creation.
> But in solution 2 we are not creating a redundant pattern matching,
> and we don't need to check it in flow rules, so it is more efficient.
> 
>> Since (2) is *not a matching criteria*, but just a hint, (1)
>> flow rules must have matching criteria anyway.
> 
> No we don't need the matching criteria ANY_VPORT with solution (2)
> because we are already matching on an IP src which is a vport.
> 
>>> +Table Attribute: Specialize
>>> +^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>> +
>>> +Application can help optimizing underlayer resources and insertion rate
>>> +by specializing template table.
>>> +Specialization is done by providing hints
>>> +in the template table attribute ``specialize``.
>>> +
>>> +This attribute is not mandatory for each PMD to implement.
>>> +If a hint is not supported, it will be silently ignored,
>>> +and no special optimization is done.
>>> +
>>> +If a table is specialized, the application should make sure the rules
>>> +comply with the table attribute.
>>
>> If a table is specialized, the application must make sure that
>> all flow rules added to the table have pattern which implies
>> corresponding matching criteria. For example if a table is
>> specialized to be wire-origin only, pattern should have
>> represented port item with ethdev which corresponds to a
>> physical port (or any other item which matches packets
>> coming from wire only).
> 
> No need of a matching criteria strictly mapping the hint.
> Here the hint is SPECIALIZE_TRANSFER_VPORT_ORIG
> and the rules can match on an IP src which is assigned to a vport.
> So there is no need to strictly match the vport itself in the rule.

If so, the problem is that the same rules will behave in a different way 
on different NICs.

> Hope it make thinks clear.
> We can improve the commit log as I wrote above.
> 
>