[RFC 0/3] Introduce event prefetching

[<pbhagavatula@marvell.com>]

From: Pavan Nikhilesh <pbhagavatula@marvell.com>

Event prefetching improves scheduling performance by pre-scheduling events to
event ports when dequeues are issued. This series introduces various types and
levels of prefetching to the eventdev library.

Prefetching Types:
 * RTE_EVENT_DEV_PREFETCH_NONE: No prefetching.
 * RTE_EVENT_DEV_PREFETCH: Always issue a prefetch when dequeue is issued.
 * RTE_EVENT_DEV_PREFETCH_INTELLIGENT: Delay issuing prefetch until there
   are no forward progress constraints with the held flow contexts.

Prefetching Levels:
 * Event Device Level Prefetch: Prefetching can be enabled or disabled at the
   event device during configuration. Event devices can indicate prefetching
   capabilities using `RTE_EVENT_DEV_CAP_EVENT_PREFETCH` and
  `RTE_EVENT_DEV_CAP_EVENT_INTELLIGENT_PREFETCH` via the event device info
  function `info.event_dev_cap`.
 * Event Port Level Prefetch: Prefetching can be selectively enabled or disabled
   at the event port during runtime. Event devices can indicate this capability
   using `RTE_EVENT_PORT_CAP_EVENT_PER_PORT_PREFETCH` via the event device info
   function `info.event_port_cap`.
 * Application Controlled Prefetch Hint: Applications can provide hints to the
   event device to start prefetching events using the new API
   `rte_event_port_prefetch`. Event devices can indicate this capabilities using
   `RTE_EVENT_DEV_CAP_SW_PREFETCH` via the event device info function
   `info.event_dev_cap`.

The rte_event_dequeue_burst operation initiates the prefetch operation, which
completes in parallel without affecting the dequeued event flow context and
dequeue latency. On the next dequeue operation, the prefetched events are
dequeued, and prefetch is initiated again.

In the case of application-controlled prefetch hints, the currently held flow
contexts, if any, are not affected by the prefetch operation. On the next
dequeue operation, the prefetched events are returned, but prefetch is not
initiated again until the application provides the hint again. If prefetching
is already enabled at the event device level or event port level,
the hint is ignored.

Pavan Nikhilesh (3):
  eventdev: introduce event prefetching
  eventdev: allow event ports to modified prefetches
  eventdev: add SW event prefetch hint

 app/test/test_eventdev.c                    | 113 +++++++++++++++
 doc/guides/prog_guide/eventdev/eventdev.rst |  42 ++++++
 lib/eventdev/eventdev_pmd.h                 |   4 +
 lib/eventdev/eventdev_private.c             |  19 +++
 lib/eventdev/eventdev_trace_points.c        |   6 +
 lib/eventdev/rte_eventdev.h                 | 152 ++++++++++++++++++++
 lib/eventdev/rte_eventdev_core.h            |   9 ++
 lib/eventdev/rte_eventdev_trace_fp.h        |  19 ++-
 lib/eventdev/version.map                    |   6 +
 9 files changed, 369 insertions(+), 1 deletion(-)

--
2.46.0