[dpdk-dev] [PATCH] doc: note KNI alternatives and deprecation plan

[Olivier Matz]

Hi Ferruh,

Few minor comments below.

On Wed, Jun 23, 2021 at 06:31:42PM +0100, Ferruh Yigit wrote:
> Add a note that KNI kernel module will be moved to dpdk-kmods git repo
> and there is a long term plan to deprecate it.
> 
> Also add some more details on the alternatives to KNI and cons of the
> KNI against these alternatives.
> 
> Signed-off-by: Ferruh Yigit <ferruh.yigit at intel.com>
> ---
>  doc/guides/nics/tap.rst                       |  2 +
>  .../prog_guide/kernel_nic_interface.rst       | 38 +++++++++++++++++--
>  2 files changed, 37 insertions(+), 3 deletions(-)
> 
> diff --git a/doc/guides/nics/tap.rst b/doc/guides/nics/tap.rst
> index 3ce696b605d1..07315fe32422 100644
> --- a/doc/guides/nics/tap.rst
> +++ b/doc/guides/nics/tap.rst
> @@ -1,6 +1,8 @@
>  ..  SPDX-License-Identifier: BSD-3-Clause
>      Copyright(c) 2016 Intel Corporation.
>  
> +.. _TunTap_PMD:
> +
>  Tun|Tap Poll Mode Driver
>  ========================
>  
> diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
> index 1ce03ec1a374..29f8c92fd9d6 100644
> --- a/doc/guides/prog_guide/kernel_nic_interface.rst
> +++ b/doc/guides/prog_guide/kernel_nic_interface.rst
> @@ -6,16 +6,48 @@
>  Kernel NIC Interface
>  ====================
>  
> +.. Note::
> +
> +   KNI kernel module will be removed from main git repository to `dpdk-kmods <https://git.dpdk.org/dpdk-kmods/>`_

removed -> moved?

Or "removed from main and moved to"

> +   repository by the `DPDK technical board decision <https://mails.dpdk.org/archives/dev/2021-January/197077.html>`_.
> +   Also there is a `long term plan <https://mails.dpdk.org/archives/dev/2021-May/209026.html>`_ to deprecate the KNI.
> +
> +   :ref:`virtio_user_as_exceptional_path` alternative is preferred way for
> +   interfacing with Linux network stack as it is being in-kernel solution and
> +   similar performance expectations.
> +
>  The DPDK Kernel NIC Interface (KNI) allows userspace applications access to the Linux* control plane.
>  
> -The benefits of using the DPDK KNI are:
> +KNI allows an interface with the kernel network stack and allows management of
> +DPDK ports using standard Linux net tools such as ``ethtool``, ``ifconfig`` and
> +``tcpdump``.
> +
> +Main use case of KNI is get/receive exception packets from/to Linux network
> +stack while main datapath IO is done bypassing the networking stack.
> +
> +There are other alternatives to KNI, all are available in the upstream Linux:
> +
> +#. :ref:`TunTap_PMD` as wrapper to `Linux tun/tap
> +   <https://www.kernel.org/doc/Documentation/networking/tuntap.txt>`_
> +
> +#. :ref:`virtio_user_as_exceptional_path`

Shouldn't virtio_user be the first item?

> +
> +The benefits of using the DPDK KNI against alternatives are:
>  
>  *   Faster than existing Linux TUN/TAP interfaces
>      (by eliminating system calls and copy_to_user()/copy_from_user() operations.
>  
> -*   Allows management of DPDK ports using standard Linux net tools such as ethtool, ifconfig and tcpdump.
> +The cons of the DPDK KNI are:
> +
> +* It is out-of-tree Linux kernel module and it can't be distributed as binary as
> +  part of OSV DPDK packages. This makes it harder to consume, although it is

OSV -> OVS

> +  always possible to compile it from the source code.
> +
> +* As it shares memory between userspace and kernelspace, and kernel part
> +  directly uses input provided by userspace, it is not safe. This makes hard to
> +  upstream the module.
>  
> -*   Allows an interface with the kernel network stack.
> +* Only a subset of control commands are supported by KNI.
>  
>  The components of an application using the DPDK Kernel NIC Interface are shown in :numref:`figure_kernel_nic_intf`.
>  
> -- 
> 2.31.1
>