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From: Ferruh Yigit <ferruh.yigit@amd.com>
To: Thomas Monjalon <thomas@monjalon.net>
CC: <dev@dpdk.org>, Olivier Matz <olivier.matz@6wind.com>, David Marchand
<david.marchand@redhat.com>, Stephen Hemminger <stephen@networkplumber.org>,
Elad Nachman <eladv6@gmail.com>, Igor Ryzhov <iryzhov@nfware.com>, Dan Gora
<dg@adax.com>, =?UTF-8?q?Morten=20Br=C3=B8rup?= <mb@smartsharesystems.com>
Subject: [PATCH v5] doc: note KNI alternatives
Date: Thu, 24 Nov 2022 11:40:40 +0000
Message-ID: <20221124114041.3169291-1-ferruh.yigit@amd.com>
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Add more information on alternatives of KNI and the disadvantages of KNI
against these alternatives.
Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
---
Cc: Olivier Matz <olivier.matz@6wind.com>
Cc: David Marchand <david.marchand@redhat.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Elad Nachman <eladv6@gmail.com>
Cc: Igor Ryzhov <iryzhov@nfware.com>
Cc: Dan Gora <dg@adax.com>
Cc: Morten Brørup <mb@smartsharesystems.com>
v5:
* Rebased
* Dedicated kernel core added as disadvantage
---
.../prog_guide/kernel_nic_interface.rst | 35 ++++++++++++++++---
1 file changed, 30 insertions(+), 5 deletions(-)
diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst b/doc/guides/prog_guide/kernel_nic_interface.rst
index 6a564f61cad8..cac0ab0cb278 100644
--- a/doc/guides/prog_guide/kernel_nic_interface.rst
+++ b/doc/guides/prog_guide/kernel_nic_interface.rst
@@ -11,8 +11,9 @@ Kernel NIC Interface
KNI is deprecated and will be removed in future.
See :doc:`../rel_notes/deprecation`.
- For an alternative to KNI, that does not require any out-of-tree Linux kernel modules,
- or a custom library, see :ref:`virtio_user_as_exception_path`.
+ :ref:`virtio_user_as_exception_path` alternative is the preferred way for
+ interfacing with the Linux network stack as it is an in-kernel solution and
+ has similar performance expectations.
.. note::
@@ -21,14 +22,38 @@ Kernel NIC Interface
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``, ``ifconfig`` 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
(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:
+
+* It is out-of-tree Linux kernel module and it can't be distributed as binary as
+ part of operating system vendor 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.
+
+* Requires dedicated kernel cores.
-* Allows an interface with the kernel network stack.
+* 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`.
--
2.25.1