Re: [dpdk-dev] [PATCH 01/27] eventdev: dlb upstream prerequisites

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, Jun 30, 2020 at 5:06 PM Kinsella, Ray <mdr@ashroe.eu> wrote:
>
>
>
> On 30/06/2020 12:30, Jerin Jacob wrote:
> > On Tue, Jun 30, 2020 at 4:52 PM Kinsella, Ray <mdr@ashroe.eu> wrote:
> >>
> >>
> >>
> >> On 27/06/2020 08:44, Jerin Jacob wrote:
> >>>> +
> >>>> +/** Event port configuration structure */
> >>>> +struct rte_event_port_conf_v20 {
> >>>> +       int32_t new_event_threshold;
> >>>> +       /**< A backpressure threshold for new event enqueues on this port.
> >>>> +        * Use for *closed system* event dev where event capacity is limited,
> >>>> +        * and cannot exceed the capacity of the event dev.
> >>>> +        * Configuring ports with different thresholds can make higher priority
> >>>> +        * traffic less likely to  be backpressured.
> >>>> +        * For example, a port used to inject NIC Rx packets into the event dev
> >>>> +        * can have a lower threshold so as not to overwhelm the device,
> >>>> +        * while ports used for worker pools can have a higher threshold.
> >>>> +        * This value cannot exceed the *nb_events_limit*
> >>>> +        * which was previously supplied to rte_event_dev_configure().
> >>>> +        * This should be set to '-1' for *open system*.
> >>>> +        */
> >>>> +       uint16_t dequeue_depth;
> >>>> +       /**< Configure number of bulk dequeues for this event port.
> >>>> +        * This value cannot exceed the *nb_event_port_dequeue_depth*
> >>>> +        * which previously supplied to rte_event_dev_configure().
> >>>> +        * Ignored when device is not RTE_EVENT_DEV_CAP_BURST_MODE capable.
> >>>> +        */
> >>>> +       uint16_t enqueue_depth;
> >>>> +       /**< Configure number of bulk enqueues for this event port.
> >>>> +        * This value cannot exceed the *nb_event_port_enqueue_depth*
> >>>> +        * which previously supplied to rte_event_dev_configure().
> >>>> +        * Ignored when device is not RTE_EVENT_DEV_CAP_BURST_MODE capable.
> >>>> +        */
> >>>>         uint8_t disable_implicit_release;
> >>>>         /**< Configure the port not to release outstanding events in
> >>>>          * rte_event_dev_dequeue_burst(). If true, all events received through
> >>>> @@ -733,6 +911,14 @@ struct rte_event_port_conf {
> >>>>  rte_event_port_default_conf_get(uint8_t dev_id, uint8_t port_id,
> >>>>                                 struct rte_event_port_conf *port_conf);
> >>>>
> >>>> +int
> >>>> +rte_event_port_default_conf_get_v20(uint8_t dev_id, uint8_t port_id,
> >>>> +                               struct rte_event_port_conf_v20 *port_conf);
> >>>> +
> >>>> +int
> >>>> +rte_event_port_default_conf_get_v21(uint8_t dev_id, uint8_t port_id,
> >>>> +                                     struct rte_event_port_conf *port_conf);
> >>>
> >>> Hi Timothy,
> >>>
> >>> + ABI Maintainers (Ray, Neil)
> >>>
> >>> # As per my understanding, the structures can not be versioned, only
> >>> function can be versioned.
> >>> i.e we can not make any change to " struct rte_event_port_conf"
> >>
> >> So the answer is (as always): depends
> >>
> >> If the structure is being use in inline functions is when you run into trouble
> >> - as knowledge of the structure is embedded in the linked application.
> >>
> >> However if the structure is _strictly_ being used as a non-inlined function parameter,
> >> It can be safe to version in this way.
> >
> > But based on the optimization applied when building the consumer code
> > matters. Right?
> > i.e compiler can "inline" it, based on the optimization even the
> > source code explicitly mentions it.
>
> Well a compiler will typically only inline within the confines of a given object file, or
> binary, if LTO is enabled.

>
> If a function symbol is exported from library however, it won't be inlined in a linked application.

Yes, With respect to that function.
But the application can use struct rte_event_port_conf in their code
and it can be part of other structures.
Right?


> The compiler doesn't have enough information to inline it.
> All the compiler will know about it is it's offset in memory, and it's signature.
>
> >
> >
> >>
> >> So just to be clear, it is still the function that is actually being versioned here.
> >>
> >>>
> >>> # We have a similar case with ethdev and it deferred to next release v20.11
> >>> http://patches.dpdk.org/patch/69113/
> >>
> >> Yes - I spent a why looking at this one, but I am struggling to recall,
> >> why when I looked it we didn't suggest function versioning as a potential solution in this case.
> >>
> >> Looking back at it now, looks like it would have been ok.
> >
> > Ok.
> >
> >>
> >>>
> >>> Regarding the API changes:
> >>> # The slow path changes general looks good to me. I will review the
> >>> next level in the coming days
> >>> # The following fast path changes bothers to me. Could you share more
> >>> details on below change?
> >>>
> >>> diff --git a/app/test-eventdev/test_order_atq.c
> >>> b/app/test-eventdev/test_order_atq.c
> >>> index 3366cfc..8246b96 100644
> >>> --- a/app/test-eventdev/test_order_atq.c
> >>> +++ b/app/test-eventdev/test_order_atq.c
> >>> @@ -34,6 +34,8 @@
> >>>                         continue;
> >>>                 }
> >>>
> >>> +               ev.flow_id = ev.mbuf->udata64;
> >>> +
> >>> # Since RC1 is near, I am not sure how to accommodate the API changes
> >>> now and sort out ABI stuffs.
> >>> # Other concern is eventdev spec get bloated with versioning files
> >>> just for ONE release as 20.11 will be OK to change the ABI.
> >>> # While we discuss the API change, Please send deprecation notice for
> >>> ABI change for 20.11,
> >>> so that there is no ambiguity of this patch for the 20.11 release.
> >>>