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doc: note KNI alternatives

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Add more information on alternatives of KNI
and the disadvantages of KNI compared to these alternatives.

Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
This commit is contained in:
Ferruh Yigit 2022-11-24 17:15:24 +00:00 committed by Thomas Monjalon
parent 50b2a419d0
commit e0b2658529
1 changed files with 31 additions and 5 deletions
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36
doc/guides/prog_guide/kernel_nic_interface.rst
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@ -11,8 +11,9 @@ Kernel NIC Interface
KNI is deprecated and will be removed in future. KNI is deprecated and will be removed in future.
See :doc:`../rel_notes/deprecation`. See :doc:`../rel_notes/deprecation`.
For an alternative to KNI, that does not require any out-of-tree Linux kernel modules, :ref:`virtio_user_as_exception_path` alternative is the preferred way
or a custom library, see :ref:`virtio_user_as_exception_path`. for interfacing with the Linux network stack
as it is an in-kernel solution and has similar performance expectations.
.. note:: .. note::
@ -21,14 +22,39 @@ Kernel NIC Interface
The DPDK Kernel NIC Interface (KNI) allows userspace applications access to the Linux* control plane. The DPDK Kernel NIC Interface (KNI) allows userspace applications access to the Linux* control plane.
The benefits of using the DPDK KNI are: KNI provides an interface with the kernel network stack
and allows management of DPDK ports using standard Linux net tools
such as ``ethtool``, ``iproute2`` and ``tcpdump``.
The main use case of KNI is to 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:`virtio_user_as_exception_path`
#. :doc:`../nics/tap` as wrapper to `Linux tun/tap
<https://www.kernel.org/doc/Documentation/networking/tuntap.txt>`_
The benefits of using the KNI against alternatives are:
* Faster than existing Linux TUN/TAP interfaces * Faster than existing Linux TUN/TAP interfaces
(by eliminating system calls and copy_to_user()/copy_from_user() operations. (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 disadvantages of the KNI are:
* Allows an interface with the kernel network stack. * It is out-of-tree Linux kernel module
which makes updating and distributing the driver more difficult.
Most users end up building the KNI driver from source
which requires the packages and tools to build kernel modules.
* 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.
* Requires dedicated kernel cores.
* Only a subset of net devices 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`. The components of an application using the DPDK Kernel NIC Interface are shown in :numref:`figure_kernel_nic_intf`.