Yes missed somehow 6. One more general comment, what happened until now? The Mark is already implemented and working more then 2 years.
> -----Original Message----- > From: Andrew Rybchenko <arybche...@solarflare.com> > Sent: Friday, November 8, 2019 2:20 PM > To: Ori Kam <or...@mellanox.com>; Zhang, Qi Z <qi.z.zh...@intel.com>; > Thomas Monjalon <tho...@monjalon.net> > Cc: dev@dpdk.org; pbhagavat...@marvell.com; Yigit, Ferruh > <ferruh.yi...@intel.com>; jer...@marvell.com; Mcnamara, John > <john.mcnam...@intel.com>; Kovacevic, Marko > <marko.kovace...@intel.com>; Adrien Mazarguil > <adrien.mazarg...@6wind.com>; david.march...@redhat.com; > ktray...@redhat.com; Olivier Matz <olivier.m...@6wind.com> > Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add flow action type update as > an offload > > On 11/8/19 3:12 PM, Ori Kam wrote: > > > > Hi Andrew, > > > > Thanks very much for the summery, I think this makes the discussion much > better. > > (we even got some new folks 😊) > > > > I vote for B and C, > > > > Please read my comments below. > > > > Ori > > > >> -----Original Message----- > >> From: dev <dev-boun...@dpdk.org> On Behalf Of Zhang, Qi Z > >> Sent: Friday, November 8, 2019 1:41 PM > >> To: Thomas Monjalon <tho...@monjalon.net>; Andrew Rybchenko > >> <arybche...@solarflare.com> > >> Cc: Ori Kam <or...@mellanox.com>; dev@dpdk.org; > >> pbhagavat...@marvell.com; Yigit, Ferruh <ferruh.yi...@intel.com>; > >> jer...@marvell.com; Mcnamara, John <john.mcnam...@intel.com>; > >> Kovacevic, Marko <marko.kovace...@intel.com>; Adrien Mazarguil > >> <adrien.mazarg...@6wind.com>; david.march...@redhat.com; > >> ktray...@redhat.com; Olivier Matz <olivier.m...@6wind.com> > >> Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add flow action type update > as > >> an offload > >> > >> > >> > >>> -----Original Message----- > >>> From: dev <dev-boun...@dpdk.org> On Behalf Of Thomas Monjalon > >>> Sent: Friday, November 8, 2019 7:04 PM > >>> To: Andrew Rybchenko <arybche...@solarflare.com> > >>> Cc: Ori Kam <or...@mellanox.com>; dev@dpdk.org; > >>> pbhagavat...@marvell.com; Yigit, Ferruh <ferruh.yi...@intel.com>; > >>> jer...@marvell.com; Mcnamara, John <john.mcnam...@intel.com>; > >>> Kovacevic, Marko <marko.kovace...@intel.com>; Adrien Mazarguil > >>> <adrien.mazarg...@6wind.com>; david.march...@redhat.com; > >>> ktray...@redhat.com; Olivier Matz <olivier.m...@6wind.com> > >>> Subject: Re: [dpdk-dev] [PATCH 1/2] ethdev: add flow action type > update as > >> an > >>> offload > >>> > >>> 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. > >>>>>> > > > > I don’t agree that this method is implicit it is quit explicit, do we > > support it in > PMD > > with the use case or not. Sound very explicit. You can argue that the PMD > uses > > validation flow to understand that it need to support MARK, but from > every perspective > > it is more correct . what does it mean if the application enabled mark and > never download a flow? > > It is implicit from PMD point of view, since there is no command > to enable it. The decision to enable is the result of seen > attempt to validate mark. If few rules are validated, but an > application decides to have it disabled finally, how to achieve it? > Last validation attempt wins? > Other points are covered by (6) below. > > >>>>>> 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. > >>>>>> > > > > This is not true, for example the PMD support Mark only in Nic mode > > While the application needs E-Switch then the PMD reports incorrectly. > > Or for example if the mark is supported only as only action, and the > application needs > > decap and mark. this means that the user will never be able to use the > mark > > so the PMD uses slower Rx function without the mark ever being used. > > It is covered by (6) below. > > >>>>>> 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. > >>>>>> > > > > You forgot a one more very important reason, the fact that the mark > > may be supported only on some flows. So if the user needs mark with > decap > > and this combination is not supported the user will never we able to use > mark > > while using mark Rx function. So you get slow data path with no ability to > use it. > > Again, see (6) below. > > >>>>>> 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? > >>> > >>> Note that A and C will not guarantee that the offload will be possible. > >>> We need B (flow rule validation) anyway. > >> > >> I may not understand how solution B can works well for all the cases. > >> > > > > That is the point of solution B it always work, it is a bit harder to use > > maybe, > > but you can check and decide everything. > > > >> A rte_flow rule can be issued after dev_start, which means the rx_burst > >> function is already selected at that time, > >> so does that mean the driver need to switch from a non- mark offload > aware > >> path to a mark offload aware path without stop device? or it has to reject > the > >> flow? > >> The question is if we have 2 data path, one support some offload , one > not > >> but more fast, which one should be selected during dev_start? Isn't > Offload > >> widely used to solve this problem? > >> > >> I think the option A solve all the problems, option C might also works, but > A is > >> looks much straightforward for me. > >> > > > > Solution A my result in selecting incorrect datapath please see my answer > above. > > > > As you can guess I'm in favor of B and C (C need B) > > > >> Regards > >> Qi > >> > >> > >>> > >>> It seems A, B, C are not alternatives but all required as pieces of a > puzzle... > >>> > >
