Re: [dpdk-dev] [RFC v2 0/1] add flow action context API

[Andrey Vesnovaty <andrey.vesnovaty@gmail.com>]

On Sun, Jun 28, 2020 at 4:42 PM Jerin Jacob <jerinjacobk@gmail.com> wrote:

> On Sun, Jun 28, 2020 at 2:14 PM Andrey Vesnovaty
> <andrey.vesnovaty@gmail.com> wrote:
> >
> > Hi
> >
> > On Fri, Jun 26, 2020 at 2:44 PM Jerin Jacob <jerinjacobk@gmail.com>
> wrote:
> >>
> >> On Sat, Jun 20, 2020 at 7:02 PM Andrey Vesnovaty
> >> <andrey.vesnovaty@gmail.com> wrote:
> >> >
> >> > Hi, and thanks a lot for your RFC v1 comments.
> >> >
> >> > RFC v2 emphasize the intent for sharing the flow action:
> >> > * The term 'action context' was unclear and replaced with
> >> >    'shared action'.
> >> > * RFC v2 subject became 'add flow shared action API'.
> >> > * all proposed APIs renamed according the above.
> >> >
> >> > The new shared action is an independent entity decoupled from any flow
> >> > while any flow can reuse such an action. Please go over the RFC
> >> > description, it was almost entirely rewritten.
> >> >
> >> > @Jerin Jacob:
> >> > Thanks again for your comments, it made me admit that v1 description
> was
> >> > incomplete & unclear.  I hope v2 will be better at least in terms of
> >> > clarity.
> >>
> >> The public API and its usage is very clear. Thanks for this RFC.
> >
> >
> > My pleasure.
> >>
> >>
> >> I think, RFC v2 still not addressing the concern raised in the
> >> http://mails.dpdk.org/archives/dev/2020-June/169296.html.
> >>
> >> Since MLX hardware has an HW based shared object it is fine to have
> >> public API based on that level of abstraction.
> >> But at the PMD driver level we need to choose the correct abstraction
> >> to support all PMD and support shared object scheme if possible.
> >>
> >> I purpose to introduce something below or similar
> >>             int (*action_update)
> >>                 (struct rte_eth_dev *,
> >>                   struct rte_flow *flow,
> >>                  const struct rte_flow_action [],
> >>                  struct rte_flow_error *);
> >
> > Where this callback suppose to belong (struct rte_flow_ops)?
>
> Yes.
>
> > How should it be implemented by PMD?
>
> See below,
>
> > Is it about shared action and if "yes" why there is 'flow' argument?
>
> flow holds the "pattern" and "action" data as PMD specific handle.
> So PMD, implementation can just change that action if it gets the PMD
> specific handle.
>
>
> >>
> >>
> >> in addition to: shared_action_create, shared_action_destroy,
> >> shared_action_update, shared_action_query
> >>
> >> Have generic implementation of above, if action_update callback is not
> >> NULL.
> >
> > "is not NULL" -> "is NULL"?
>
> Yes. When it is NULL.


Jerin, few clarifications regarding generic implementation of shared action:
Based on this conversation I'm assuming that generic implementation
supposed to be something like:
For each flow using some shared action:
call ops-> action_update()
If the assumption above correct:
1. taking into account that shared_action_update() is atomic, how can this
deal with partial success: some flows may fail validation - should it:
  1.1.lock all flows
  1.2.validate all flows
  1.3.update all flows
  1.4. unlock
2. action_update callback is PMD specific & if it's unsupported there is no
support for shared action any way
Please address the issues above

>
> >>
> >> So that, it can work all PMDs and to
> >> avoid the duplication of "complex" shared session management code.
> >
> > Do you mean shared action in use by multiple flows by "shared session"?
>
> Yes.
>
Common 'shared session' management code:
- can be reduced to atomic usage counter
- maintaining list of flow using shared action expected to impact
performance & not necessary for all PMD specific implementations
Access to other shared resources hard to generalize because:
- for some PMDs mutual exclusion is HW feature & no need to protect it in SW
- for others there may be multiple resources & access to each one protected
by different mechanism

An observation related to action_update callback:
If replaced (updated) action was shared then the flow won't be influenced
any more by updates or removed shared action.