Re: [RFC 3/3] rte_flow: add new action for traffic metering and policing

["Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>]

Hi Adrien,

Thanks for reviewing this proposal.

> -----Original Message-----
> From: Adrien Mazarguil [mailto:adrien.mazarguil@6wind.com]
> Sent: Thursday, June 1, 2017 4:14 PM
> To: Dumitrescu, Cristian <cristian.dumitrescu@intel.com>
> Cc: dev@dpdk.org; thomas@monjalon.net;
> jerin.jacob@caviumnetworks.com; hemant.agrawal@nxp.com; Doherty,
> Declan <declan.doherty@intel.com>; Wiles, Keith <keith.wiles@intel.com>
> Subject: Re: [RFC 3/3] rte_flow: add new action for traffic metering and
> policing
> 
> Hi Cristian,
> 
> On Tue, May 30, 2017 at 05:44:13PM +0100, Cristian Dumitrescu wrote:
> > Signed-off-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>
> > ---
> >  lib/librte_ether/rte_flow.h | 22 ++++++++++++++++++++++
> >  1 file changed, 22 insertions(+)
> >
> > diff --git a/lib/librte_ether/rte_flow.h b/lib/librte_ether/rte_flow.h
> > index c47edbc..2942ca7 100644
> > --- a/lib/librte_ether/rte_flow.h
> > +++ b/lib/librte_ether/rte_flow.h
> > @@ -881,6 +881,14 @@ enum rte_flow_action_type {
> >  	 * See struct rte_flow_action_vf.
> >  	 */
> >  	RTE_FLOW_ACTION_TYPE_VF,
> > +
> > +	/**
> > +	 * Traffic metering and policing (MTR).
> > +	 *
> > +	 * See struct rte_flow_action_meter.
> > +	 * See file rte_mtr.h for MTR object configuration.
> > +	 */
> > +	RTE_FLOW_ACTION_TYPE_METER,
> >  };
> >
> >  /**
> > @@ -974,6 +982,20 @@ struct rte_flow_action_vf {
> >  };
> >
> >  /**
> > + * RTE_FLOW_ACTION_TYPE_METER
> > + *
> > + * Traffic metering and policing (MTR).
> > + *
> > + * Packets matched by items of this type can be either dropped or passed
> to the
> > + * next item with their color set by the MTR object.
> > + *
> > + * Non-terminating by default.
> > + */
> > +struct rte_flow_action_meter {
> > +	uint32_t mtr_id; /**< MTR object ID created with rte_mtr_create().
> */
> > +};
> > +
> > +/**
> >   * Definition of a single action.
> >   *
> >   * A list of actions is terminated by a END action.
> 
> Assuming this action is provided to the underlying PMD, can you describe
> what happens next; what is a PMD supposed to do when creating the flow
> rule
> and the impact on its data path?
> 

Metering is just another flow action that needs to be supported by rte_flow API.

Typically, NICs supporting this action have an array of metering & policing contexts on their data path, which are abstracted as MTR objects in our API.
- rte_mtr_create() configures an MTR object, with no association to any of the known flows yet.
	- On NIC side, the driver configures one of the available metering & policing contexts.
- rte_flow_create() defines the flow (match rule) and its set of actions, with metering & policing as one of the actions.
	- On NIC side, the driver configures a flow/filter for traffic classification/distribution/bifurcation, with the metering & policing context enabled for this flow.

At run-time, any packet matching this flow will execute this action, which involves metering (packet is assigned a color) and policing (packet may be recolored or dropped, as configured), with stats being updated as well.

> It looks like mtr_id is arbitrarily set by the user calling
> rte_mtr_create(), which means the PMD has to look up the associated MTR
> context somehow.
> 
> How about making the rte_mtr_create() API return an opaque rte_mtr
> object
> pointer provided back to all API functions as well as through this action
> instead, and not leave it up to the user?
> 

Of course, it can be done this way as well, but IMHO probably not the best idea from the application perspective. We had a similar discussion when we defined the ethdev traffic management API [1].

Object handles can be integers, void pointers or pointers to opaque structures, and each of these approaches are allowed and used by DPDK APIs. Here is an example why I think using integers for MTR object handle makes the life of the application easier:
- Let's assume we have several actions for a flow (a1, a2, a3, ...).
- When handles are pointers to opaque structures, app typically needs to save all of them in a per flow data structure: struct a1 *p1, struct a2 *p2, struct a3 *p3.
	-This results in increased complexity and size for the app tables, which can be avoided.
- When handles are integers generated by the app as opposed of driver, the app can simply use a single index - let's cal it flow_id - and register it as the handle to each of these flow actions.
	- No more fake tables.
	- No more worries about the pointer being valid in one address space and not valid in another.

There is some handle lookup to be done by the driver, but this is a trivial task,  and checking the validity of the handle (input parameter) is the first thing done by any API function, regardless of which handle style is used.

[1] http://www.dpdk.org/ml/archives/dev/2017-February/057368.html


> --
> Adrien Mazarguil
> 6WIND

Regards,
Cristian