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

[Ferruh Yigit]

On 6/23/2021 7:33 PM, Stephen Hemminger wrote:
> On Wed, 23 Jun 2021 18:31:42 +0100
> Ferruh Yigit <ferruh.yigit at intel.com> 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/>`_
>> +   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`
>> +
>> +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
>> +  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`.
>>  
> 
> You should also link to virtio user as exception path. In my testing virtio is as fast as KNI and uses less CPU.
> 

Patch mentions from virtio-user alternative, and in the notes it even documents
it as preferred way.