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

[Andrew Rybchenko]

On 2/1/23 12:05, Thomas Monjalon wrote:
> 01/02/2023 10:00, Ori Kam:
>> Hi all,
>>
>> Sorry for jumping in late,
>>
>>> -----Original Message-----
>>> From: Jerin Jacob <jerinjacobk at gmail.com>
>>> Sent: Wednesday, 1 February 2023 10:53
>>>
>>> On Wed, Feb 1, 2023 at 12:46 PM Andrew Rybchenko
>>> <andrew.rybchenko at 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 at monjalon.net>
>>>>>>> wrote:
>>>>>>>>
>>>>>>>> 27/01/2023 11:42, Nithin Kumar Dabilpuram:
>>>>>>>>> From: Thomas Monjalon <thomas at monjalon.net>
>>>>>>>>>> 27/01/2023 06:02, Nithin Kumar Dabilpuram:
>>>>>>>>>>> From: Thomas Monjalon <thomas at 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.

Sorry, I'm lost here. Don't we need to enable FAST_FREE
offload? As far as I know all offloads are disabled 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.
>>>>
>>
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