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?
