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

[Thomas Monjalon <thomas@monjalon.net>]

02/02/2023 10:21, Andrew Rybchenko:
> 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.

I think I get it now.
You suggest to have pattern items for VPORT and PHY_PORT,
so the user won't be tempted to use hint for such matching?
We used to have RTE_FLOW_ITEM_TYPE_PHY_PORT, we could think about it.

> Anyway, hint itself is OK and makes sense. Hopefully
> documentation highlights that pattern match is required.

Yes we did an effort to highlight what are hints in the last version.

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