Re: [dpdk-dev] [PATCH v4] doc: add new tables for rte flow items and actions support

[Ajit Khaparde <ajit.khaparde@broadcom.com>]

[-- Attachment #1: Type: text/plain, Size: 4386 bytes --]

On Wed, Feb 17, 2021 at 2:49 AM Thomas Monjalon <thomas@monjalon.net> wrote:

> 17/02/2021 11:37, Ferruh Yigit:
> > On 2/17/2021 5:57 AM, Asaf Penso wrote:
> > > From: Ferruh Yigit <ferruh.yigit@intel.com>
> > >> On 2/7/2021 10:52 AM, Asaf Penso wrote:
> > >>> In http://doc.dpdk.org/guides/nics/overview.html, table 1.1 lists
> all
> > >>> supported features.
> > >>> It has a single line for "Flow API" that refers to rte_flow support.
> > >>> rte_flow is composed of many items and actions that are not expressed
> > >>> in this single line.
> > >>>
> > >>> The following new tables are suggested:
> > >>> 1. rte_flow items
> > >>> 2. rte_flow actions
> > >>>
> > >>
> > >> Hi Asaf,
> > >>
> > >> I understand the intention, but I am not sure about this.
> > >>
> > >> The Flow API does not provide a capability or feature list in the API
> level, by
> > >> design, because it is very hard to do it correct, but this patch
> tries to do it in the
> > >> documentation level.
> > >>
> > >> This will be missing lots of details, the flow items and actions
> documented as
> > >> supported may and may not be supported based on the details.
> > >>
> > >
> > > Which missing details are you referring to? All flow items and all
> actions are listed.
> > >
> >
> > Patterns are complex, any rule can be valid or invalid based on provided
> pattern
> > values (details), also any rule can be valid or invalid based on
> previous rules
> > or configuration.
> >
> > In practice this information is much more useful if it is provided by
> API, but
> > we are not able to do it because of its complex nature, it should be
> same level
> > of complexity to provide this information by documentation.
> >
> > >> It will be very hard to read this table (when it becomes full), also
> will be very hard
> > >> to maintain.
> > >
> > > As part of any documentation change in rte_flow the developer would
> also need to update this table.
> > > Why would it be very hard to maintain?
> >  >
> >
> > Ahh, that sound so simple when you say like this :) In practice even
> keeping
> > feature list requiring lots of effort, developers are
> > missing/neglecting/ignoring updating documentation when updating the
> code.
> >
> > And for this case is partially correct table a useful information? If
> this is
> > not completely correct people won't rely on it and it will become just
> useless.
> > So this feature should come with an automated way to detect if a rule
> supported
> > but not documented, or even better this table should be generated from
> code
> > automatically.
> >
> > >>
> > >>
> > >> Let me start with a question, who do you think will be your consumer?
> > >> Who will benefit from this table and how?
> > >
> > > We get a lot of questions from users regarding rte_flow support and we
> do not have a single place with proper documentation.
> > > I can ask the same about the overall feature table, right? There is a
> value to document the support.
> > >
> >
> > Let's discuss the feature table separately, I think that is a valid
> question.
> >
> > For the rte_flow, who is asking questions? End user, or application
> developer?
> > So is this intended to be a marketing documentation or technical
> documentation?
> >
> > And what is the nature of the questions, if it is related to the
> rte_flow, there
> > is already a proper documentation for it:
> > https://doc.dpdk.org/guides/prog_guide/rte_flow.html
> >
> > If this question is if any specific rule supported by a specific PMD,
> right now
> > only valid way to say this that I am aware of is, run
> 'rte_flow_validate()' and see.
> > Not sure if we can document this properly.
>
> I think in general we are missing a big disclaimer
> on top of this overview page:
>         Each feature may have some hardware limitations.
>
> Then there is a need, both for application developers and end-users,
> to know which feature can be supported by a PMD,
> or which PMD can support a feature.
> Yes there are complex limitations with hardware offloads in general.
> Yes it would be nice to report some tested capabilities with a CI.
> But it does not mean we should not try to document it in my opinion.
>
+1 to all of these.
A document like this will help give an idea on what is possible with the
PMD without looking at the code. Beyond that, the user can check with
the vendor/developer for specific details if needed.