Re: [PATCH v3 10/11] eventdev: clarify docs on event object fields and op types

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, Feb 20, 2024 at 11:09 PM Bruce Richardson
<bruce.richardson@intel.com> wrote:
>
> On Fri, Feb 09, 2024 at 02:44:04PM +0530, Jerin Jacob wrote:
> > On Fri, Feb 2, 2024 at 6:11 PM Bruce Richardson
> > <bruce.richardson@intel.com> wrote:
> > >
> > > Clarify the meaning of the NEW, FORWARD and RELEASE event types.
> > > For the fields in "rte_event" struct, enhance the comments on each to
> > > clarify the field's use, and whether it is preserved between enqueue and
> > > dequeue, and it's role, if any, in scheduling.
> > >
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > > V3: updates following review
> > > ---
> > >  lib/eventdev/rte_eventdev.h | 161 +++++++++++++++++++++++++-----------
> > >  1 file changed, 111 insertions(+), 50 deletions(-)
> > >
> > > diff --git a/lib/eventdev/rte_eventdev.h b/lib/eventdev/rte_eventdev.h
> > > index 8d72765ae7..58219e027e 100644
> > > --- a/lib/eventdev/rte_eventdev.h
> > > +++ b/lib/eventdev/rte_eventdev.h
> > > @@ -1463,47 +1463,54 @@ struct rte_event_vector {
> > >
> > >  /* Event enqueue operations */
> > >  #define RTE_EVENT_OP_NEW                0
> > > -/**< The event producers use this operation to inject a new event to the
> > > - * event device.
> > > +/**< The @ref rte_event.op field must be set to this operation type to inject a new event,
> > > + * i.e. one not previously dequeued, into the event device, to be scheduled
> > > + * for processing.
> > >   */
> > >  #define RTE_EVENT_OP_FORWARD            1
> > > -/**< The CPU use this operation to forward the event to different event queue or
> > > - * change to new application specific flow or schedule type to enable
> > > - * pipelining.
> > > +/**< The application must set the @ref rte_event.op field to this operation type to return a
> > > + * previously dequeued event to the event device to be scheduled for further processing.
> > >   *
> > > - * This operation must only be enqueued to the same port that the
> > > + * This event *must* be enqueued to the same port that the
> > >   * event to be forwarded was dequeued from.
> > > + *
> > > + * The event's fields, including (but not limited to) flow_id, scheduling type,
> > > + * destination queue, and event payload e.g. mbuf pointer, may all be updated as
> > > + * desired by the application, but the @ref rte_event.impl_opaque field must
> > > + * be kept to the same value as was present when the event was dequeued.
> > >   */
> > >  #define RTE_EVENT_OP_RELEASE            2
> > >  /**< Release the flow context associated with the schedule type.
> > >   *
> > > - * If current flow's scheduler type method is *RTE_SCHED_TYPE_ATOMIC*
> > > - * then this function hints the scheduler that the user has completed critical
> > > - * section processing in the current atomic context.
> > > - * The scheduler is now allowed to schedule events from the same flow from
> > > - * an event queue to another port. However, the context may be still held
> > > - * until the next rte_event_dequeue_burst() call, this call allows but does not
> > > - * force the scheduler to release the context early.
> > > - *
> > > - * Early atomic context release may increase parallelism and thus system
> > > + * If current flow's scheduler type method is @ref RTE_SCHED_TYPE_ATOMIC
> > > + * then this operation type hints the scheduler that the user has completed critical
> > > + * section processing for this event in the current atomic context, and that the
> > > + * scheduler may unlock any atomic locks held for this event.
> > > + * If this is the last event from an atomic flow, i.e. all flow locks are released,
> >
> >
> > Similar comment as other email
> > [Jerin] When there are multiple atomic events dequeue from @ref
> > rte_event_dequeue_burst()
> > for the same event queue, and it has same flow id then the lock is ....
> >
> > [Mattias]
> > Yes, or maybe describing the whole lock/unlock state.
> >
> > "The conceptual per-queue-per-flow lock is in a locked state as long
> > (and only as long) as one or more events pertaining to that flow were
> > scheduled to the port in question, but are not yet released."
> >
> > Maybe it needs to be more meaty, describing what released means. I don't
> > have the full context of the documentation in my head when I'm writing this.
> >
>
> Will take a look to reword a bit
>
> >
> > > + * the scheduler is now allowed to schedule events from that flow from to another port.
> > > + * However, the atomic locks may be still held until the next rte_event_dequeue_burst()
> > > + * call; enqueuing an event with opt type @ref RTE_EVENT_OP_RELEASE allows,
> >
> > Is ";" intended?
> >
> > > + * but does not force, the scheduler to release the atomic locks early.
> >
> > instead of "not force", can use the term _hint_ the driver and reword.
>
> Ok.
> >
> > > + *
> > > + * Early atomic lock release may increase parallelism and thus system
> > >   * performance, but the user needs to design carefully the split into critical
> > >   * vs non-critical sections.
> > >   *
> > > - * If current flow's scheduler type method is *RTE_SCHED_TYPE_ORDERED*
> > > - * then this function hints the scheduler that the user has done all that need
> > > - * to maintain event order in the current ordered context.
> > > - * The scheduler is allowed to release the ordered context of this port and
> > > - * avoid reordering any following enqueues.
> > > - *
> > > - * Early ordered context release may increase parallelism and thus system
> > > - * performance.
> > > + * If current flow's scheduler type method is @ref RTE_SCHED_TYPE_ORDERED
> > > + * then this operation type informs the scheduler that the current event has
> > > + * completed processing and will not be returned to the scheduler, i.e.
> > > + * it has been dropped, and so the reordering context for that event
> > > + * should be considered filled.
> > >   *
> > > - * If current flow's scheduler type method is *RTE_SCHED_TYPE_PARALLEL*
> > > - * or no scheduling context is held then this function may be an NOOP,
> > > - * depending on the implementation.
> > > + * Events with this operation type must only be enqueued to the same port that the
> > > + * event to be released was dequeued from. The @ref rte_event.impl_opaque
> > > + * field in the release event must have the same value as that in the original dequeued event.
> > >   *
> > > - * This operation must only be enqueued to the same port that the
> > > - * event to be released was dequeued from.
> > > + * If a dequeued event is re-enqueued with operation type of @ref RTE_EVENT_OP_RELEASE,
> > > + * then any subsequent enqueue of that event - or a copy of it - must be done as event of type
> > > + * @ref RTE_EVENT_OP_NEW, not @ref RTE_EVENT_OP_FORWARD. This is because any context for
> > > + * the originally dequeued event, i.e. atomic locks, or reorder buffer entries, will have
> > > + * been removed or invalidated by the release operation.
> > >   */
> > >
> > >  /**
> > > @@ -1517,56 +1524,110 @@ struct rte_event {
> > >                 /** Event attributes for dequeue or enqueue operation */
> > >                 struct {
> > >                         uint32_t flow_id:20;
> > > -                       /**< Targeted flow identifier for the enqueue and
> > > -                        * dequeue operation.
> > > -                        * The value must be in the range of
> > > -                        * [0, nb_event_queue_flows - 1] which
> > > -                        * previously supplied to rte_event_dev_configure().
> > > +                       /**< Target flow identifier for the enqueue and dequeue operation.
> > > +                        *
> > > +                        * For @ref RTE_SCHED_TYPE_ATOMIC, this field is used to identify a
> > > +                        * flow for atomicity within a queue & priority level, such that events
> > > +                        * from each individual flow will only be scheduled to one port at a time.
> > > +                        *
> > > +                        * This field is preserved between enqueue and dequeue when
> > > +                        * a device reports the @ref RTE_EVENT_DEV_CAP_CARRY_FLOW_ID
> > > +                        * capability. Otherwise the value is implementation dependent
> > > +                        * on dequeue.
> > >                          */
> > >                         uint32_t sub_event_type:8;
> > >                         /**< Sub-event types based on the event source.
> > > +                        *
> > > +                        * This field is preserved between enqueue and dequeue.
> > > +                        * This field is for application or event adapter use,
> > > +                        * and is not considered in scheduling decisions.
> >
> >
> > cnxk driver is considering this for scheduling decision to
> > differentiate the producer i.e event adapters.
> > If other drivers are not then we can change the language around it is
> > implementation defined.
> >
> How does the event type influence the scheduling decision? I can drop the

For cnxk, From HW POV, the flow ID is 32 bit which is divided between
flow_id(20 bit), sub event type(8bit) and
event type(4bit)

> last line here

Yes. Please


 > but it seems strange to me that the type of event could affect
> things. I would have thought that with the eventdev API only the queue,
> flow id, and priority would be factors in scheduling?

>
> >
> > > +                        *
> > >                          * @see RTE_EVENT_TYPE_CPU
> > >                          */
> > >                         uint32_t event_type:4;
> > > -                       /**< Event type to classify the event source.
> > > -                        * @see RTE_EVENT_TYPE_ETHDEV, (RTE_EVENT_TYPE_*)
> > > +                       /**< Event type to classify the event source. (RTE_EVENT_TYPE_*)
> > > +                        *
> > > +                        * This field is preserved between enqueue and dequeue
> > > +                        * This field is for application or event adapter use,
> > > +                        * and is not considered in scheduling decisions.
> >
> >
> > cnxk driver is considering this for scheduling decision to
> > differentiate the producer i.e event adapters.
> > If other drivers are not then we can change the language around it is
> > implementation defined.
> >
> > >                          */
> > >                         uint8_t op:2;
> > > -                       /**< The type of event enqueue operation - new/forward/
> > > -                        * etc.This field is not preserved across an instance
> > > -                        * and is undefined on dequeue.
> > > -                        * @see RTE_EVENT_OP_NEW, (RTE_EVENT_OP_*)
> > > +                       /**< The type of event enqueue operation - new/forward/ etc.
> > > +                        *
> > > +                        * This field is *not* preserved across an instance
> > > +                        * and is implementation dependent on dequeue.
> > > +                        *
> > > +                        * @see RTE_EVENT_OP_NEW
> > > +                        * @see RTE_EVENT_OP_FORWARD
> > > +                        * @see RTE_EVENT_OP_RELEASE
> > >                          */
> > >                         uint8_t rsvd:4;
> > > -                       /**< Reserved for future use */
> > > +                       /**< Reserved for future use.
> > > +                        *
> > > +                        * Should be set to zero on enqueue.
> >
> > I am worried about some application explicitly start setting this to
> > zero on every enqueue.
> > Instead, can we say application should not touch the field, Since every eventdev
> > operations starts with dequeue() driver can fill to the correct value.
> >
>
> I'll set this to zero on "NEW", or untouched on FORWARD/RELEASE.

OK

> If we don't state that it should be zeroed on NEW or untouched
> otherwise we cannot use the space in future without ABI break.
>
> > > +                        */
> > >                         uint8_t sched_type:2;
> > >                         /**< Scheduler synchronization type (RTE_SCHED_TYPE_*)
> > >                          * associated with flow id on a given event queue
> > >                          * for the enqueue and dequeue operation.
> > > +                        *
> > > +                        * This field is used to determine the scheduling type
> > > +                        * for events sent to queues where @ref RTE_EVENT_QUEUE_CFG_ALL_TYPES
> > > +                        * is configured.
> > > +                        * For queues where only a single scheduling type is available,
> > > +                        * this field must be set to match the configured scheduling type.
> > > +                        *
> > > +                        * This field is preserved between enqueue and dequeue.
> > > +                        *
> > > +                        * @see RTE_SCHED_TYPE_ORDERED
> > > +                        * @see RTE_SCHED_TYPE_ATOMIC
> > > +                        * @see RTE_SCHED_TYPE_PARALLEL
> > >                          */
> > >                         uint8_t queue_id;
> > >                         /**< Targeted event queue identifier for the enqueue or
> > >                          * dequeue operation.
> > > -                        * The value must be in the range of
> > > -                        * [0, nb_event_queues - 1] which previously supplied to
> > > -                        * rte_event_dev_configure().
> > > +                        * The value must be less than @ref rte_event_dev_config.nb_event_queues
> > > +                        * which was previously supplied to rte_event_dev_configure().
> >
> > Some reason, similar text got removed for flow_id. Please add the same.
> >
>
> That was deliberate based on discussion on V2. See:
>
> http://inbox.dpdk.org/dev/Zby3nb4NGs8T5odL@bricha3-MOBL.ger.corp.intel.com/
>
> and wider thread discussion starting here:
>
> http://inbox.dpdk.org/dev/ZbvOtAEpzja0gu7b@bricha3-MOBL.ger.corp.intel.com/
>
> Basically, the comment is wrong based on what the code does now. No event
> adapters or apps are limiting the flow-id, and nothing seems broken, so we
> can remove the comment.

OK

>