Re: [dpdk-dev] [PATCH v2 3/3] ethdev: improve flow mark Rx offload deprecation notice

[Jerin Jacob <jerinjacobk@gmail.com>]

On Sat, Nov 23, 2019 at 3:58 AM Thomas Monjalon <thomas@monjalon.net> wrote:
>
> 22/11/2019 12:53, Andrew Rybchenko:
> > On 11/22/19 2:15 PM, Thomas Monjalon wrote:
> > > 22/11/2019 11:12, Andrew Rybchenko:
> > >> On 11/22/19 1:01 AM, Thomas Monjalon wrote:
> > >>> 19/11/2019 13:12, Andrew Rybchenko:
> > >>>> The deprecation notice is required since it adds more requirements
> > >>>> when RTE flow mark and flag actions may be used and require
> > >>>> changes in applications.
> > >>> I am still not sure what is the best solution here.
> > >>> I continued to think about it in this thread:
> > >>>   http://mails.dpdk.org/archives/dev/2019-November/151960.html
> > >>>
> > >>> I think we cannot require any application change until 20.11
> > >>> in order to keep API (and behaviour) compatibility.
> > >> Expected, but still very disappointing.
> > >>
> > >> The feature is implemented by Pavan (@ Marvell), supported by me,
> > >> used by Qi (@ Intel), looks better than alternatives from application
> > >> developer point of view [1] and finally postponed for 1 year without really
> > >> strong motivation.
> > >
> > > I see different valuable point of views. This is enough motivation.
> >
> > It looks like I miss it in previous discussion, I would be thankful if
> > you give me links to read or hints how to find.
>
> http://mails.dpdk.org/archives/dev/2019-November/150793.html
>
> > Introducing new types of controls would make configuration more and
> > more complex. I think that many different types of control would
> > over-complicate it. May be it is unavoidable, but it should be clear
> > why the problem cannot be solved using existing types of controls
> > (e.g. offloads).
>
> The offload control is used as an effective configuration for now.
> The features which are configured with DEV_RX_OFFLOAD_*
> do not need any other API to be used.
> Extending DEV_RX_OFFLOAD_* bits for enabling features which
> must be configured via other API anyway, is possible.
> The real problem is that features in DEV_RX_OFFLOAD_* are supposed
> to be disabled by default. If we add some opt-in features here,
> we cannot enable them by default for API compatibility and do the
> right thing by default.
>
> Choosing DEV_RX_OFFLOAD_* bits or rte_eth_dev_opt* functions is a detail.
> The real decision is to change the API for using all these features.
> Can we keep all features available by default (opt-out)?

IMO, *rte_eth_dev_opt* has following problems

1) It is not multi-process friendly. If we are changing the Rx/Tx
function pointer, based on
the selected offload, then, using *rte_eth_dev_opt* scheme won't
really work(if the new API
called after the secondary process launch)

2) If we are taking rte_eth_dev_opt path then by default feature has
to be enabled to
not break the functional ABI. That scheme won't scale if as when we
keep adding the new features.
It is always easy for the application to define "what it wants" vs
"what it does not want"

3) Defining the device state after the reconfigure operation.

IMO, if any operation is connected to fastpath it is better to use
DEV_RX_OFFLOAD_ like
this feature where enable or disable PMDs from updating
``rte_mbuf::hash::fdir`` so that if possible
we can use different Rx function pointer if possible(Hence it can work
with the multi-process case case)