Re: [PATCH v3 1/4] ethdev: add group counter support to rte_flow

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

Hi Mohammad,

On Mon, Apr 09, 2018 at 03:22:45PM +0100, Mohammad Abdul Awal wrote:
> Hi Adrien,
> 
> 
> On 06/04/2018 21:26, Adrien Mazarguil wrote:
> > On Fri, Apr 06, 2018 at 01:24:00PM +0100, Declan Doherty wrote:
> > > Add new RTE_FLOW_ACTION_TYPE_GROUP_COUNT action type to enable shared
> > > counters across multiple flows on a single port or across multiple
> > > flows on multiple ports within the same switch domain.
> > > 
> > > Introduce new API rte_flow_query_group_count to allow querying of group
> > > counters.
> > > 
> > > Signed-off-by: Declan Doherty <declan.doherty@intel.com>
> > Both features are definitely needed, however I suggest to enhance the
> > existing action type and query function instead, given the rte_flow ABI
> > won't be maintained for the 18.05 release [1].
> > 
> > Counters and query support were defined as a kind of PoC in preparation for
> > future requirements back in DPDK 17.02 and so far few PMDs have implemented
> > the query callback (mlx5 and failsafe, and the latter isn't really a PMD).
> > 
> > Due to the behavior change of action lists [2], providing an action type as
> > a query parameter is not specific enough anymore, for instance if a list
> > contains multiple COUNT, the application should be able to tell which needs
> > to be queried.
> > 
> > Therefore I suggest to redefine the query function as follows:
> > 
> >   int
> >   rte_flow_query(uint16_t port_id,
> >                  struct rte_flow *flow,
> >                  const struct rte_flow_action *action,
> >                  void *data,
> >                  struct rte_flow_error *error);
> > 
> > Third argument is an action definition with the same configuration (if any)
> > as previously defined in the action list originally used to create the flow
> > rule (not necessarily the same pointer, only the contents matter).
> > 
> > It means two perfectly identical actions can't be distinguished, and that's
> > how group counters will work.
> > Instead of adding a new action type to distinguish groups, a configuration
> > structure is added to the existing RTE_FLOW_ACTION_TYPE_COUNT, with
> > non-shared counters as a default behavior:
> > 
> >   struct rte_flow_action_count {
> >           uint32_t shared:1; /**< Share counter ID with other flow rules. */
> >           uint32_t reserved:31; /**< Reserved, must be zero. */
> >           uint32_t id; /**< Counter ID. */
> >   };
> > 
> > Doing so will impact some existing code in mlx5 and librte_flow_classify,
> > but that shouldn't be much of an issue.
> > 
> > Keep in mind testpmd and its documentation must be updated as well.
> > 
> > Thoughts?
> Please correct me if I am wrong but I think we are talking two different
> things here.
> If I understood you correctly, you are proposing to pass a list of actions
> (instead if a action type) in the third parameter to perform multiple
> actions in the same query call. Lets take an example for 100 ingress flows.
> So, if we want to query the counter for all the flows, we can get them by a
> single query providing a list (of size 100) of action_count in the 3rd
> param.

Whoa no! I'm only suggesting a pointer to a single action as a replacement
for the basic action type, not a *list* of actions. I hope this addresses
all concerns :)

The fact the action in question would refer to a shared counter (see struct
above) with a given ID would be enough to make all counters with the same ID
refer to the same internal PMD object.

> On the other hand, we are saying that all the flows are belongs to same
> tunnel end-point (we are talking only 1 TEP here), then the PMD will be
> responsible to increment the counter of TEP for matching all the flows (100
> flows). So, using one group query by passing one action_count in 3rd param,
> we can get the count of the TEP.
> 
> This case is generic enough for sure for simple flows but may not be
> suitable for tunnel cases, as application needs to track the counters for
> all the flows, and needs to build the list of action each time the flows
> added/deleted.

I think we're on the same page. I'm only suggesting to define a
configuration structure for the COUNT action (which currently doesn't take
any) as a replacement for GROUP_COUNT, and tweak the query callback to be
able to tell a specific counter to query instead of adding a new query
callback and leaving the existing one broken by design.

> > A few nits below for the sake of commenting.
> > 
> > [1] "Flow API overhaul for switch offloads"
> >      http://dpdk.org/ml/archives/dev/2018-April/095774.html
> > [2] "ethdev: alter behavior of flow API actions"
> >      http://dpdk.org/ml/archives/dev/2018-April/095779.html

-- 
Adrien Mazarguil
6WIND