Re: [dpdk-dev] [RFC PATCH 0/7] RFC:EventDev OPDL PMD

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

-----Original Message-----
> Date: Fri, 24 Nov 2017 11:23:45 +0000
> From: liang.j.ma@intel.com
> To: jerin.jacob@caviumnetworks.com
> CC: dev@dpdk.org, harry.van.haaren@intel.com, bruce.richardson@intel.com,
>  deepak.k.jain@intel.com, john.geary@intel.com
> Subject: [RFC PATCH 0/7] RFC:EventDev OPDL PMD
> X-Mailer: git-send-email 2.7.5
> 
> From: Liang Ma <liang.j.ma@intel.com>


Thanks Liang Ma for the RFC.

> 
> The OPDL (Ordered Packet Distribution Library) eventdev is a specific
> implementation of the eventdev API. It is particularly suited to packet
> processing workloads that have high throughput and low latency 
> requirements. All packets follow the same path through the device.
> The order which packets  follow is determinted by the order in which
> queues are set up. Packets are left on the ring until they are transmitted.
> As a result packets do not go out of order.
> 
> Features:
> 
> The OPDL eventdev implements a subset of features of the eventdev API;
> 
> Queues
>  * Atomic
>  * Ordered (Parallel is supported as parallel is a subset of Ordered)
>  * Single-Link
> 
> Ports
>  * Load balanced (for Atomic, Ordered, Parallel queues)
>  * Single Link (for single-link queues)
> 
> Single Port Queue
> 
> It is possible to create a Single Port Queue 
> RTE_EVENT_QUEUE_CFG_SINGLE_LINK. Packets dequeued from this queue do
> not need to be re-enqueued (as is the case with an ordered queue). The 
> purpose of this queue is to allow for asynchronous handling of packets in 
> the middle of a pipeline. Ordered queues in the middle of a pipeline 
> cannot delete packets.
> 
> 
> Queue Dependencies
> 
> As stated the order in which packets travel through queues is static in
> nature. They go through the queues in the order the queues are setup at
> initialisation rte_event_queue_setup(). For example if an application
> sets up 3 queues, Q0, Q1, Q2 and has 3 assoicated ports P0, P1, P2 and 
> P3 then packets must be
> 
>  * Enqueued onto Q0 (typically through P0), then
> 
>  * Dequeued from Q0 (typically through P1), then
> 
>  * Enqueued onto Q1 (also through P1), then
> 
>  * Dequeued from Q2 (typically through P2),  then
> 
>  * Enqueued onto Q3 (also through P2), then
> 
>  * Dequeued from Q3 (typically through P3) and then transmitted on the 
>    relevant eth port
> 
> 
> Limitations
> 
> The opdl implementation has a number of limitations. These limitations are
> due to the static nature of the underlying queues. It is because of this
> that the implementation can achieve such high throughput and low latency
> 
> The following list is a comprehensive outline of the what is supported and
> the limitations / restrictions imposed by the opdl pmd
> 
>  - The order in which packets moved between queues is static and fixed 
>    (dynamic scheduling is not supported).
> 
>  - NEW, RELEASE op type are not explicitly supported. RX (first enqueue) 
>    implicitly adds NEW event types, and TX (last dequeue) implicitly does
>    RELEASE event types.
> 
>  - All packets follow the same path through device queues.
> 
>  - Flows within queues are NOT supported.
> 
>  - Event priority is NOT supported.
> 
>  - Once the device is stopped all inflight events are lost. Applications should 
>    clear all inflight events before stopping it.
> 
>  - Each port can only be associated with one queue.
> 
>  - Each queue can have multiple ports associated with it.
> 
>  - Each worker core has to dequeue the maximum burst size for that port.
> 
>  - For performance, the rte_event flow_id should not be updated once 
>     packet is enqueued on RX.

Some top-level comments,

# How does application knows this PMD has above limitations?

I think, We need to add more capability RTE_EVENT_DEV_CAP_*
to depict these constraints. On the same note, I believe this
PMD is "radically" different than other SW/HW PMD then anyway
we cannot write the portable application using this PMD. So there
is no point in abstracting it as eventdev PMD. Could you please
work on the new capabilities are required to enable this PMD.
If it needs more capability flags to express this PMD capability,
we might have a different library for this as it defects the
purpose of portable eventdev applications.

# We should not add yet another "PMD" specific example application
in example area like "examples/eventdev_pipeline_opdl_pmd". We are
working on making examples/eventdev/pipeline_sw_pmd to make work
on both HW and SW.

# We should not add new PMD specific test cases in
test/test/test_eventdev_opdl.c area.I think existing PMD specific
test case can be moved to respective driver area, and it can do 
the self-test by passing some command line arguments to vdev.

# Do you have relative performance number with exiting SW PMD?
Meaning how much it improves for any specific use case WRT exiting
SW PMD. That should a metric to define the need for new PMD.

# There could be another SW driver from another vendor like ARM.
So, I think, it is important to define the need for another SW
PMD and how much limitation/new capabilities it needs to define to
fit into the eventdev framework,

Jerin

> Reference
> General concept of event driven programming model
> [http://dpdk.org/doc/guides/eventdevs/index.html]
> 
> Original Ordered Pipeline Design slides 
> [https://dpdksummit.com/Archive/pdf/2017Asia/DPDK-China2017-Ma-OPDL.pdf]
> 
> 
> Liang Ma (7):
>   event/opdl:  add the opdl ring infrastructure library
>   event/opdl: add the opdl pmd header and init helper function
>   event/opdl: add the opdl pmd main body and xstats helper function
>   event/opdl: update the build system to enable compilation of pmd
>   test/eventdev: opdl eventdev pmd unit test func and makefiles
>   examples/eventdev_pipeline_opdl: adding example
>   doc: add eventdev opdl pmd docuement and example usage document
> 
>  config/common_base                                 |    6 +
>  doc/guides/eventdevs/index.rst                     |    1 +
>  doc/guides/eventdevs/opdl.rst                      |  162 +++
>  .../sample_app_ug/eventdev_pipeline_opdl_pmd.rst   |  128 +++
>  doc/guides/sample_app_ug/index.rst                 |    1 +
>  drivers/event/Makefile                             |    1 +
>  drivers/event/opdl/Makefile                        |   65 ++
>  drivers/event/opdl/opdl_evdev.c                    |  714 ++++++++++++
>  drivers/event/opdl/opdl_evdev.h                    |  353 ++++++
>  drivers/event/opdl/opdl_evdev_init.c               |  945 ++++++++++++++++
>  drivers/event/opdl/opdl_evdev_xstats.c             |  205 ++++
>  drivers/event/opdl/opdl_ring.c                     | 1170 ++++++++++++++++++++
>  drivers/event/opdl/opdl_ring.h                     |  578 ++++++++++
>  drivers/event/opdl/rte_pmd_evdev_opdl_version.map  |    3 +
>  examples/eventdev_pipeline_opdl_pmd/Makefile       |   49 +
>  examples/eventdev_pipeline_opdl_pmd/main.c         |  766 +++++++++++++
>  mk/rte.app.mk                                      |    1 +
>  test/test/Makefile                                 |    1 +
>  test/test/test_eventdev_opdl.c                     | 1089 ++++++++++++++++++
>  19 files changed, 6238 insertions(+)
>  create mode 100644 doc/guides/eventdevs/opdl.rst
>  create mode 100644 doc/guides/sample_app_ug/eventdev_pipeline_opdl_pmd.rst
>  create mode 100644 drivers/event/opdl/Makefile
>  create mode 100644 drivers/event/opdl/opdl_evdev.c
>  create mode 100644 drivers/event/opdl/opdl_evdev.h
>  create mode 100644 drivers/event/opdl/opdl_evdev_init.c
>  create mode 100644 drivers/event/opdl/opdl_evdev_xstats.c
>  create mode 100644 drivers/event/opdl/opdl_ring.c
>  create mode 100644 drivers/event/opdl/opdl_ring.h
>  create mode 100644 drivers/event/opdl/rte_pmd_evdev_opdl_version.map
>  create mode 100644 examples/eventdev_pipeline_opdl_pmd/Makefile
>  create mode 100644 examples/eventdev_pipeline_opdl_pmd/main.c
>  create mode 100644 test/test/test_eventdev_opdl.c
> 
> -- 
> 2.7.5
> 
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