[v6] doc: note KNI alternatives
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Commit Message
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>
v6:
* s/ifconfig/iproute2/
* reword distributing binary module disadvantage
v5:
* Rebased
* Dedicated kernel core added as disadvantage
---
.../prog_guide/kernel_nic_interface.rst | 35 ++++++++++++++++---
1 file changed, 30 insertions(+), 5 deletions(-)
Comments
24/11/2022 18:15, Ferruh Yigit:
> Add more information on alternatives of KNI and the disadvantages of KNI
> against these alternatives.
>
> Signed-off-by: Ferruh Yigit <ferruh.yigit@amd.com>
Applied, thanks.
@@ -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``, ``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
(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 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.
-* 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`.