On 11/19/2019 11:09 AM, Thomas Monjalon wrote: > 19/11/2019 11:59, Andrew Rybchenko: >> On 11/19/19 12:50 PM, Thomas Monjalon wrote: >>> 19/11/2019 10:24, Andrew Rybchenko: >>>> On 11/8/19 4:30 PM, Thomas Monjalon wrote: >>>>> 08/11/2019 14:27, Andrew Rybchenko: >>>>>> 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. >>>>> Yes it is experimental and I think it is too late to align now. >>>>> >>>>> Anyway, we will probably to discuss again these offloads TAG/MARK/META, >>>>> as requested by several people. >>>>> >>>> The series implements (A) to help to solve the problem described above. >>>> What is the fate of the series in v19.11 in accordance with the >>>> discussion? >>> I am against adding anything related to a feature union'ed in mbuf. >>> The feature must move to dynamic field first. >>> >>> In addition, such capability is very weak. >>> I am not sure it is a good idea to have some weak capabilities, >>> meaning a feature could be available but not in all cases. >>> I think we should discuss more generally how we want to handle >>> the rte_flow capabilities conveniently and reliably. >> >> It is really unexpected outcome from the above discussion. > > I'm sorry, I thought I was clear in my request to switch to dynamic first. > > >> It is just possibility to deliver and handle marks on datapath and >> request to have it. It says almost nothing about rte_flow rules >> supported etc. I'll be happy to take part in the discussion. >> >>> So regarding 19.11, as this feature is not new, it can wait 20.02. >> >> OK, it is not critical for me, so I don't mind, however, I've seen >> patches which try to use it [1] except net/octeontx2 in the second >> patch of the series. >> >> [1] https://patches.dpdk.org/patch/62415/ >
Sorry, I have to resurrect this old (long) discussion because the patches are still active in the patchwork [1] and the deprecation notice is still there [2]. Andrew has a good summary in the thread [3], after a year nothing seems changed. Pavan, Thomas, Andrew, Ori, What is our plan with this series, lets try to have a conclusion. [1] https://patches.dpdk.org/user/todo/dpdk/?series=7076 [2] http://lxr.dpdk.org/dpdk/v20.05/source/doc/guides/rel_notes/deprecation.rst#L88 [3] http://inbox.dpdk.org/dev/f170105b-9c60-1b04-cb18-52e0951dd...@solarflare.com/
