Re: [PATCH v3 1/2] doc: note KNI alternatives

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 12/1/2021 4:31 PM, Morten Brørup wrote:
>> From: Ferruh Yigit [mailto:ferruh.yigit@intel.com]
>> Sent: Wednesday, 24 November 2021 18.16
>>
>> Add more information on alternatives of KNI and the cons of KNI against
>> these alternatives.
>>
>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
>> ---
>> Cc: Olivier Matz Olivier Matz <olivier.matz@6wind.com>
>> Cc: David Marchand David Marchand <david.marchand@redhat.com>
>> Cc: Stephen Hemminger Stephen Hemminger <stephen@networkplumber.org>
>> Cc: Elad Nachman <eladv6@gmail.com>
>> Cc: Igor Ryzhov <iryzhov@nfware.com>
>> Cc: Dan Gora <dg@adax.com>
>>
>> v3:
>> * reference tap document directly instead of adding label to it.
>> ---
>>  .../prog_guide/kernel_nic_interface.rst       | 34 +++++++++++++++++--
>>  1 file changed, 31 insertions(+), 3 deletions(-)
>>
>> diff --git a/doc/guides/prog_guide/kernel_nic_interface.rst
>> b/doc/guides/prog_guide/kernel_nic_interface.rst
>> index 1ce03ec1a374..f5a8b7c0782c 100644
>> --- a/doc/guides/prog_guide/kernel_nic_interface.rst
>> +++ b/doc/guides/prog_guide/kernel_nic_interface.rst
>> @@ -6,16 +6,44 @@
>>  Kernel NIC Interface
>>  ====================
>>
>> +.. Note::
>> +
>> +   :ref:`virtio_user_as_exceptional_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.
>> +
>>  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_exceptional_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 cons of the KNI are:
> 
> Consider if "disadvantages" is more appropriate than "cons". (I'm not a native English speaker.)
> 

Both fine for me, OK to use 'disadvantages'.

>> +
>> +* 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.
>>
>> -*   Allows an interface with the kernel network stack.
>> +* Only a subset of net devices control commands are supported by KNI.
> 
> If it is still relevant, add something along the lines of:
> * Requires dedicated kernel cores.
> 

ack

>>
>>  The components of an application using the DPDK Kernel NIC Interface
>> are shown in :numref:`figure_kernel_nic_intf`.
>>
>> --
>> 2.31.1
>>
> 
> Could you perhaps also promote the virtio-user documentation by moving it from the HowTo Guides to the Programmer's Guide?
> 

Hi Morten,

This is an old patch, I assumed merged v4 by Thomas superseded this
patch, but it seems this patch was not involved in that, so I will make
a new version.

For the virtio-user documentation, no objection to move it to
programmer's guide, I hope Maxime and Chenbo can help there.