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. So regarding 19.11, as this feature is not new, it can wait 20.02.
