Re: [EXT] Re: [PATCH v5 2/2] app/testpmd: add command to process Rx metadata negotiation

[Thomas Monjalon <thomas@monjalon.net>]

01/02/2023 10:00, Ori Kam:
> Hi all,
> 
> Sorry for jumping in late,
> 
> > -----Original Message-----
> > From: Jerin Jacob <jerinjacobk@gmail.com>
> > Sent: Wednesday, 1 February 2023 10:53
> > 
> > On Wed, Feb 1, 2023 at 12:46 PM Andrew Rybchenko
> > <andrew.rybchenko@oktetlabs.ru> wrote:
> > >
> > > On 2/1/23 09:10, Ivan Malov wrote:
> > > > Hello everyone,
> > > >
> > > > Since making automatic, or implicit, offload decisions does
> > > > not belong in testpmd responsibility domain, it should be
> > > > safer to avoid calling the "negotiate metadata delivery"
> > > > API with some default selection unless the user asks to
> > > > do so explicitly, via internal CLI or app options.
> > > >
> > > > With that in mind, port config <port_id> ... sounds OK.
> > > >
> > > > PMDs that support flow primitives which can generate metadata
> > > > but, if in started state, can't enable its delivery may pass
> > > > appropriate rte_error messages to the user suggesting
> > > > they enable delivery of such metadata from NIC to PMD
> > > > first. This way, if the person operating testpmd
> > > > enters a flow create command and that fails,
> > > > they can figure out the inconsistency, stop
> > > > the port, negotiate, start and try again.
> > > >
> > > > As for non-debug applications, their developers shall
> > > > be properly informed about the problem of enabling
> > > > delivery of metadata from NIC to PMD. This way,
> > > > they will invoke the negotiate API by default
> > > > in their apps, with the feature selection (eg.
> > > > MARK) as per nature of the app's business.
> > > >
> > > > This API should indeed be helpful to some PMDs with
> > > > regard to collecting upfront knowledge like this.
> > > > At the same time, should be benign to those PMDs
> > > > who do not need this knowledge and can enable
> > > > delivery of metadata right when inserting the
> > > > flow rules. So I hope the API does not create
> > > > too much discomfort to vendors not needing it.
> > > >
> > > > Thank you.
> > > >
> > > > On Wed, 1 Feb 2023, Thomas Monjalon wrote:
> > > >
> > > >> 31/01/2023 17:17, Jerin Jacob:
> > > >>> On Fri, Jan 27, 2023 at 8:31 PM Thomas Monjalon
> > <thomas@monjalon.net>
> > > >>> wrote:
> > > >>>>
> > > >>>> 27/01/2023 11:42, Nithin Kumar Dabilpuram:
> > > >>>>> From: Thomas Monjalon <thomas@monjalon.net>
> > > >>>>>> 27/01/2023 06:02, Nithin Kumar Dabilpuram:
> > > >>>>>>> From: Thomas Monjalon <thomas@monjalon.net>
> > > >>>>>>>> Ferruh is proposing to have a command "port config <port_id>
> > ..."
> > > >>>>>>>> to configure the flags to negotiate.
> > > >>>>>>>> Are you OK with this approach?
> > > >>>>>>>
> > > >>>>>>> Yes, we are fine to have such command to enable and disable the
> > > >>>>>>> feature
> > > >>>>>>> with default being it disabled if supported by PMD.
> > > >>>>>>> Is default being disabled fine if the feature is supported by a
> > > >>>>>>> PMD ?
> > > >>>>>>
> > > >>>>>> I think the default should be enabled for ease of use.
> > > >>>>>
> > > >>>>> Since testpmd is used extensively for benchmarking purposes, we
> > > >>>>> thought it should have minimum features
> > > >>>>> enabled by default. The default testpmd doesn't have any Rx/Tx
> > > >>>>> offloads enabled(except for FAST FREE),  default
> > > >>>>> fwd mode being "iofwd" and the Rx metadata is only referenced
> > when
> > > >>>>> dumping packets.
> > > >>>>>
> > > >>>>>
> > > >>>>>> Do we have similar features disables by default?
> > > >>>>>> I mean do we know features in testpmd which require a "double
> > > >>>>>> enablement"
> > > >>>>>> like one configuration command + one rte_flow rule?
> > > >>>>>
> > > >>>>> Spec itself is that way i.e "RTE_FLOW_RULE +
> > > >>>>> RX_METADATA_NEGOTIATE(once)"
> > > >>>>>
> > > >>>>> Isn't it enough if
> > > >>>>>
> > > >>>>> #1 We have enough print when rte_flow is being create without
> > > >>>>> negotiation done and ask user to enable rx metadata using
> > > >>>>> "port config <port_id>..."
> > > >>>>> #2 Provide testpmd app arg to enable Rx metadata(for example "
> > > >>>>> --rx-metadata") like other features to avoid calling another
> > > >>>>> command before rte flow create.
> > > >>>>
> > > >>>> I'm not sure what is best.
> > > >>>> I will let others discuss this part.
> > > >>>
> > > >>> IMO, enabling something always defeat the purpose to negotiate. IMO,
> > > >>> someone needs to negotiate
> > > >>> for a feature if the feature is needed. I think, the double enablement
> > > >>> is part of the spec itself. In case, The PMD
> > > >>> drivers won't like double enablement, no need to implement the PMD
> > > >>> callback. That way, there is no change in the existing flow.
> > > >>>
> > > >>> The reason why cnxk driver thought of leveraging negotiate() feature
> > > >>> so that it helps for optimization. e.s.p
> > > >>> function template for multiprocess case as we know what features
> > > >>> needed in fastpath upfront.
> > > >>>
> > > >>> If there still concerns with patch we can take up this to TB decide
> > > >>> one way or another to make forward progress. Let us know.
> > > >>
> > > >> Ferruh, Andrew, Ori, Ivan, what is your opinion?
> > > >> Let's progress with this patch to make it in -rc1.
> > >
> > > As I understand all agreed that we need testpmd command to
> > > control negotiated Rx metadata. May be even command-line
> > > option would be useful.
> > >
> > > So, remaining question is what should be the default value in
> > > testpmd. Note that it is just testpmd question since default
> > > value in an abstract application is nothing negotiated
> > > (if I'm not mistaken).
> > >
> > > The key advantaan ge of the current behaviour is to avoid
> > > "double-enabling" in testpmd. It preserves behaviour which
> > > we had before before the API addition. It is a strong
> > > argument. Basically it puts the feature into the same
> > > basket as FAST_FREE - need an action to run faster.
> > 
> > I think, there is a disconnect here. FAST_FREE is enabled by default.
> > i.e We don't need any specific action to run faster. To align with performance
> > test application, by default the configuration should be run faster. User
> > needs to give explicit configuration to allow more offload or the one causes
> > the mpps drops. IMO, That is the theme followed in testpmd.
> > 
> > 
> I agree with Andrew, the default should stay the same, as now, PMD may already implement
> logic to only enable the feature if there is a flow rule.
> Changing the default will result in breaking applications.

That's not what is discussed here.
We are talking only about testpmd default.

> I want to suggest new approach for this feature, 
> maybe we can use the rte_flow_configure, and add a new bit that says if those
> actions are going to be used.
> What do you think?

Let's not change the API please.


> > > I see no problem in such approach.
> > >
> > > The key disadvantage is the difference in testpmd and
> > > other applications default behaviour.
> > >
> > > I'd look at the feature in the following way:
> > > if an application theoretically wants to use
> > > USER_FLAG, USER_MARK or TUNNEL_ID it must negotiate
> > > corresponding Rx metadata to ensure that the feature is
> > > available and HW is informed that application may need it.
> > > Since testpmd supports corresponding flow API actions and
> > > flow tunnels, it tries to negotiate it by default, but do
> > > not fail if the negotiation fails.
> > >
> > > So, I'd would vote to keeping the default value as is.
> > >
>