From: Andrew Rybchenko <arybchenko@solarflare.com>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: Ori Kam <orika@mellanox.com>, "dev@dpdk.org" <dev@dpdk.org>,
"pbhagavatula@marvell.com" <pbhagavatula@marvell.com>,
"ferruh.yigit@intel.com" <ferruh.yigit@intel.com>,
"jerinj@marvell.com" <jerinj@marvell.com>,
John McNamara <john.mcnamara@intel.com>,
"Marko Kovacevic" <marko.kovacevic@intel.com>,
Adrien Mazarguil <adrien.mazarguil@6wind.com>,
"david.marchand@redhat.com" <david.marchand@redhat.com>,
"ktraynor@redhat.com" <ktraynor@redhat.com>,
Olivier Matz <olivier.matz@6wind.com>,
Raslan Darawsheh <rasland@mellanox.com>
Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add flow action type update as an offload
Date: Fri, 8 Nov 2019 16:27:40 +0300 [thread overview]
Message-ID: <07223bd4-da60-5c22-d9be-8f47d56c2605@solarflare.com> (raw)
In-Reply-To: <1905522.nrmIJexB1b@xps>
On 11/8/19 4:17 PM, Thomas Monjalon wrote:
> 08/11/2019 13:00, Andrew Rybchenko:
>> On 11/8/19 2:03 PM, Thomas Monjalon wrote:
>>> 08/11/2019 11:42, Andrew Rybchenko:
>>>> On 11/8/19 1:28 PM, Thomas Monjalon wrote:
>>>>> 08/11/2019 09:35, Andrew Rybchenko:
>>>>>> The problem:
>>>>>> ~~~~~~~~~~~~
>>>>>> PMD wants to know before port start if application wants to
>>>>>> to use flow MARK/FLAG in the future. It is required because:
>>>>>>
>>>>>> 1. HW may be configured in a different way to reserve resources
>>>>>> for MARK/FLAG delivery
>>>>>>
>>>>>> 2. Datapath implementation choice may depend on it (e.g. vPMD
>>>>>> is faster, but does not support MARK)
>>>>> Thank you for the clear problem statement.
>>>>> I agree with it. This is a real design issue.
>>>>>
>>>>>
>>>>>> Discussed solutions:
>>>>>> ~~~~~~~~~~~~~~~~~~~~
>>>> May be it is not 100% clear since below are alternatives.
>>>>
>>>>>> A. Explicit Rx offload suggested by the patch.
>>>>>>
>>>>>> B. Implicit by validation of a flow rule with MARK/FLAG actions used.
>>>>>>
>>>>>> C. Use dynamic field/flag (i.e. application registers dynamic field
>>>>>> and/or flag and PMD uses lookup to solve the problem) plus part
>>>>>> of (B) to discover if a feature is supported.
>>>>> The dynamic field should be registered via a new API function
>>>>> named '<feature>_init'.
>>>>> It means the application must explicit request the feature.
>>>>> I agree this is the way to go.
>>>> If I understand your statement correctly, but (C) is not ideal since it
>>>> looks global. If registered dynamic field of mbuf and is flag that
>>>> the feature should be enabled, it is a flag to all ports/devices.
>>>>
>>>>>> All solutions require changes in applications which use these
>>>>>> features. There is a deprecation notice in place which advertises
>>>>>> DEV_RX_OFFLOAD_FLOW_MARK addition, but may be it is OK to substitute
>>>>>> it with solution (B) or (C). Solution (C) requires changes since
>>>>>> it should be combined with (B) in order to understand if
>>>>>> the feature is supported.
>>>>> I don't understand.
>>>>> Application request and PMD support are two different things.
>>>>> PMD support must be via rte_flow validation on a case by case anyway.
>>>> I mean that application wants to understand if the feature is
>>>> supported. Then, it wants to enable it. In the case of (B),
>>>> if I understand the solution correctly, there is no explicit
>>>> way to enable, PMD just detects it because of discovery is done
>>>> (that's what I mean by "implicit" and it is a drawback from my
>>>> point of view, but still could be considered). (C) solves the
>>>> problem of (B).
>>>>
>>>>>> Advantages and drawbacks of solutions:
>>>>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>> 1. The main drawback of (A) is a "duplication" since we already
>>>>>> have a way to request flow MARK using rte_flow API.
>>>>>> I don't fully agree that it is a duplication, but I agree
>>>>>> that it sounds like duplication and complicates a bit flow
>>>>>> MARK usage by applications. (B) complicates it as well.
>>>>>>
>>>>>> 2. One more drawback of the solution (A) is the necessity of
>>>>>> similar solution for META and it eats one more offload bit.
>>>>>> Yes, that's true and I think it is not a problem.
>>>>>> It would make it easier for applications to find out if
>>>>>> either MARK or META is supported.
>>>>>>
>>>>>> 3. The main advantage of the solution (A) is simplicity.
>>>>>> It is simple for application to understand if it supported.
>>>>>> It is simple in PMD to understand that it is required.
>>>>>> It is simple to disable it - just reconfigure.
>>>>>> Also it is easier to document it - just mention that
>>>>>> the offload should be supported and enabled.
>>>>>>
>>>>>> 4. The main advantage of the solution (B) is no "duplication".
>>>>>> I agree that it is valid argument. Solving the problem
>>>>>> without extra entities is always nice, but unfortunately
>>>>>> it is too complex in this case.
>>>>>>
>>>>>> 5. The main drawback of the solution (B) is the complexity.
>>>>>> It is necessary to choose a flow rule which should be used
>>>>>> as a criteria. It could be hardware dependent.
>>>>>> Complex logic is require in PMD if it wants to address the
>>>>>> problem and control MARK delivery based on validated flow
>>>>>> rules. It adds dependency between start/stop processing and
>>>>>> flow rules validation code.
>>>>>> It is pretty complicated to document it.
>>>>>>
>>>>>> 6. Useless enabling of the offload in the case of solution (A)
>>>>>> if really used flow rules do not support MARK looks like
>>>>>> drawback as well, but easily mitigated by a combination
>>>>>> with solution (B) and only required if the application wants
>>>>>> to dive in the level of optimization and complexity and
>>>>>> makes sense if application knows required flow rules in
>>>>>> advance. So, it is not a problem in this case.
>>>>>>
>>>>>> 7. Solution (C) has drawbacks of the solution (B) for
>>>>>> applications to understand if these features are supported,
>>>>>> but no drawbacks in PMD, since explicit criteria is used to
>>>>>> enable/disable (dynamic field/flag lookup).
>>>>>>
>>>>>> 8. Solution (C) is nice since it avoids "duplication".
>>>>>>
>>>>>> 9. The main drawback of the solution (C) is asymmetry.
>>>>>> As it was discussed in the case of RX_TIMESTAMP
>>>>>> (if I remember it correctly):
>>>>>> - PMD advertises RX_TIMESTAMP offload capability
>>>>>> - application enables the offload
>>>>>> - PMD registers dynamic field for timestamp
>>>>>> Solution (C):
>>>>>> - PMD advertises nothing
>>>>>> - application uses solution (B) to understand if
>>>>>> these features are supported
>>>>>> - application registers dynamic field/flag
>>>>>> - PMD does lookup and solve the problem
>>>>>> The asymmetry could be partially mitigated if RX_TIMESTAMP
>>>>>> solution is changed to require an application to register
>>>>>> dynamic fields and PMD to do lookup if the offload is
>>>>>> enabled. So, the only difference will be in no offload
>>>>>> in the case of flow MARK/FLAG and usage of complex logic
>>>>>> to understand if it is supported or no.
>>>>>> May be it would be really good since it will allow to
>>>>>> have dynamic fields registered before mempool population.
>>>>>>
>>>>>> 10. Common drawback of solutions (B) and (C) is no granularity.
>>>>>> Solution (A) may be per queue while (B) and (C) cannot be
>>>>>> per queue. Moreover (C) looks global - for all devices.
>>>>>> It could be really painful.
>>>>>>
>>>>>> (C) is nice, but I still vote for simplicity and
>>>>>> granularity of (A).
>>>>> I vote for clear separation of application needs and PMD support,
>>>>> by using the method C (dynamic fields).
>>>>> I agree timestamp must use the same path.
>>>>> I agree it's complicate because we don't know in advance whether
>>>>> a flow rule will be accepted, but that's the reality, config is complex.
>>>> Do you think that global nature of the (C) is acceptable?
>>> That's a good question.
>>> Maybe the feature request should be per port.
>>> In this case, we are back to solution A with a flag per port?
>> Offloads are natively per-queue as well, so (A) keeps the choice
>> between per-port vs per-queue to PMDs as usual.
>>
>>> Note that A and C will not guarantee that the offload will be possible.
>> Yes, definitely.
>>
>>> We need B (flow rule validation) anyway.
>> Strictly speaking (B) (checking flow rules before device
>> startup) is required if an application can predict flow
>> rules and wants to ensure that MARK offload will be usable.
>> Otherwise, it may be skipped.
> No no, I mean flow rule validation MUST be used anyway
> during the runtime before applying a rule.
> I agree it is hard to predict. I speak only about real rules.
OK, I see. Of course, flow rule validation is required at runtime.
I was rather concentrated on the stated problem solutions.
>>> It seems A, B, C are not alternatives but all required
>>> as pieces of a puzzle...
>> Unfortunately true in the most complex case.
>> Right now it will be A with B if required as explained above.
>> C will come a bit later when the field migrates to dynamic.
>>
>> May be it is even better if application registers dynamic
>> fields before an attempt to enable offload to be sure that
>> it will not fail because of impossibility to register
>> dynamic field (lack of space). I'm not sure, but it is not
>> not that important.
> Yes of course, lack of mbuf space is another reason for
> disabling the feature.
>
>> If we finally go way A, should we add offloads for META back?
>> I guess separate Rx and Tx are required.
> I would prefer to add it as dynamic flags.
> Why rushing on a very temporary solution while it is not a new issue?
Basically it means that we go just (B)+(C) in the case of META.
I have no strong opinion but thought that it could be better to
align the solution. Of course, we can wait with it. As I understand
META is an experimental feature.
next prev parent reply other threads:[~2019-11-08 13:27 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-25 15:21 pbhagavatula
2019-10-25 15:21 ` [dpdk-dev] [PATCH 2/2] drivers/net: update Rx flow flag and mark capabilities pbhagavatula
2019-10-28 10:50 ` [dpdk-dev] [PATCH 1/2] ethdev: add flow action type update as an offload Ori Kam
2019-10-28 11:53 ` Andrew Rybchenko
2019-10-28 14:00 ` Ori Kam
2019-10-31 9:49 ` Andrew Rybchenko
2019-10-31 14:49 ` Thomas Monjalon
2019-10-31 23:59 ` Zhang, Qi Z
2019-11-01 11:35 ` Andrew Rybchenko
2019-11-03 10:22 ` Ori Kam
2019-11-03 11:41 ` Andrew Rybchenko
2019-11-04 18:37 ` Ori Kam
2019-11-05 6:50 ` Andrew Rybchenko
2019-11-05 8:35 ` Ori Kam
2019-11-05 11:30 ` Andrew Rybchenko
2019-11-05 16:37 ` Ori Kam
2019-11-06 6:40 ` Andrew Rybchenko
2019-11-06 7:42 ` Ori Kam
2019-11-08 8:35 ` Andrew Rybchenko
2019-11-08 9:00 ` Tom Barbette
2019-11-08 10:28 ` Thomas Monjalon
2019-11-08 10:42 ` Andrew Rybchenko
2019-11-08 11:03 ` Thomas Monjalon
2019-11-08 11:40 ` Zhang, Qi Z
2019-11-08 12:12 ` Ori Kam
2019-11-08 12:20 ` Andrew Rybchenko
2019-11-08 12:42 ` Ori Kam
2019-11-08 13:16 ` Zhang, Qi Z
2019-11-08 13:26 ` Thomas Monjalon
2019-11-08 13:06 ` Thomas Monjalon
2019-11-08 12:00 ` Andrew Rybchenko
2019-11-08 13:17 ` Thomas Monjalon
2019-11-08 13:27 ` Andrew Rybchenko [this message]
2019-11-08 13:30 ` Thomas Monjalon
2019-11-19 9:24 ` Andrew Rybchenko
2019-11-19 9:50 ` Thomas Monjalon
2019-11-19 10:59 ` Andrew Rybchenko
2019-11-19 11:09 ` Thomas Monjalon
2020-07-03 14:34 ` Ferruh Yigit
2021-02-17 13:45 ` Ferruh Yigit
2021-02-17 14:10 ` Thomas Monjalon
2021-04-20 1:05 ` Ferruh Yigit
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