Re: [dpdk-dev] [PATCH v2 1/4] ethdev: allow negative values in flow rule types

[Ori Kam <orika@nvidia.com>]

Hi Andrew,

> -----Original Message-----
> From: Andrew Rybchenko <arybchenko@solarflare.com>
> Sent: Thursday, September 17, 2020 9:50 AM
> 
> On 9/16/20 8:21 PM, Gregory Etelson wrote:
> > From: Gregory Etelson
> > Sent: Tuesday, September 15, 2020 13:27
> > To: Andrew Rybchenko <arybchenko@solarflare.com>; Ajit Khaparde
> <ajit.khaparde@broadcom.com>
> > Cc: dpdk-dev <dev@dpdk.org>; Matan Azrad <matan@nvidia.com>; Raslan
> Darawsheh <rasland@nvidia.com>; Ori Kam <orika@nvidia.com>; Gregory
> Etelson <getelson@mellanox.com>; Ori Kam <orika@mellanox.com>; NBU-
> Contact-Thomas Monjalon <thomas@monjalon.net>; Ferruh Yigit
> <ferruh.yigit@intel.com>
> > Subject: RE: [dpdk-dev] [PATCH v2 1/4] ethdev: allow negative values in flow
> rule types
> >
> > Subject: Re: [dpdk-dev] [PATCH v2 1/4] ethdev: allow negative values in flow
> rule types
> > On 9/15/20 7:36 AM, Ajit Khaparde wrote:
> > On Tue, Sep 8, 2020 at 1:16 PM Gregory Etelson
> <mailto:getelson@nvidia.com> wrote:
> > From: Gregory Etelson <mailto:getelson@mellanox.com>
> >
> > RTE flow items & actions use positive values in item & action type.
> > Negative values are reserved for PMD private types. PMD
> > items & actions usually are not exposed to application and are not
> > used to create RTE flows.
> >
> > The patch allows applications with access to PMD flow
> > items & actions ability to integrate RTE and PMD items & actions
> > and use them to create flow rule.
> > While we are reviewing this, some quick comment/questions..
> >
> > Doesn't this go against the above "PMD
> > items & actions usually are not exposed to application and are not
> > used to create RTE flows."?
> > Why would an application try to use PMD specific private types?
> > Isn't this contrary to having a standard API?
> >
> > +1
> >
> > I would like to clarify the purpose and use of private elements patch.
> > That patch is prerequisite for  [PATCH v2 2/4] ethdev: tunnel offload model
> patch.
> > The tunnel offload API provides unified hardware independent model to
> offload tunneled packets,
> > match on packet headers in hardware and to restore outer headers of
> partially offloaded packets.
> > The model implementation depends on hardware capabilities. For example,
> if hardware supports inner nat,
> > it can do nat first and postpone decap to the end, while other hardware that
> cannot do inner nat must decap first
> > and run nat actions afterwards. Such hardware has to save outer header in
> some hardware context,
> > register or memory, for application to restore a packet later, if needed. Also,
> in this case the exact solution
> > depends on PMD because of limited number of hardware contexts.
> > Although application working with DKDK can implement all these
> requirements with existing flow rules API,
> > it will have to address each hardware specifications separately.
> > To solve this limitation we selected design where application quires PMD for
> actions, or items,
> > that are optimal for a hardware that PMD represents. Result can be a
> mixture of RTE and PMD private elements -
> > it's up to PMD implementation. Application passes these elements back to
> PMD as a flow rule recipe
> > that's already optimal for underlying hardware.
> > If PMD has private elements in such rule items or actions, these private
> elements must not be rejected by RTE layer.
> >
> > I hope it helps to understand what this model is trying to achieve.
> > Did that clarify your concerns ?
> 
> There is a very simple question which I can't answer after
> reading it.
> Why these PMD specific actions and items do not bind
> application to a specific vendor. If it binds, it should
> be clearly stated in the description. If no, I'd like to
> understand why since opaque actions/items are not really
> well defined and hardly portable across vendors.

You are correct, when looking at this patch as a stand a lone
patch using such action / items does bind the application to specific PMD.
first sometimes it is required, for example one vendor may introduce private action
to support some key costumer, or enable feature that is not supported using standard rte flow API.

The main reason for this patch is the tunnel API[1] as stated in the reply
from Gregory, the tunnel API exposes a public function that returns a list of 
actions / items. The list is generated by the PMD, so using the API is not binding
since it is generic, but the action / items returned are private but the application is not aware of those actions / items, from it's point of view it called a generic function
and got actions that are configured to do the requested job. All the application needs to do is send the actions / item as actions / item when calling flow create.

Does this answer your question?

[1] https://patches.dpdk.org/patch/76931/