35. KNI Poll Mode Driver

KNI PMD is wrapper to the librte_kni library.

This PMD enables using KNI without having a KNI specific application, any forwarding application can use PMD interface for KNI.

Sending packets to any DPDK controlled interface or sending to the Linux networking stack will be transparent to the DPDK application.

To create a KNI device net_kni# device name should be used, and this will create kni# Linux virtual network interface.

There is no physical device backend for the virtual KNI device.

Packets sent to the KNI Linux interface will be received by the DPDK application, and DPDK application may forward packets to a physical NIC or to a virtual device (like another KNI interface or PCAP interface).

To forward any traffic from physical NIC to the Linux networking stack, an application should control a physical port and create one virtual KNI port, and forward between two.

Using this PMD requires KNI kernel module be inserted.

35.1. Usage

EAL --vdev argument can be used to create KNI device instance, like:

dpdk-testpmd --vdev=net_kni0 --vdev=net_kni1 -- -i

Above command will create kni0 and kni1 Linux network interfaces, those interfaces can be controlled by standard Linux tools.

When testpmd forwarding starts, any packets sent to kni0 interface forwarded to the kni1 interface and vice versa.

There is no hard limit on number of interfaces that can be created.

35.2. Default interface configuration

librte_kni can create Linux network interfaces with different features, feature set controlled by a configuration struct, and KNI PMD uses a fixed configuration:

Interface name: kni#
force bind kernel thread to a core : NO
mbuf size: (rte_pktmbuf_data_room_size(pktmbuf_pool) - RTE_PKTMBUF_HEADROOM)
mtu: (conf.mbuf_size - RTE_ETHER_HDR_LEN)

KNI control path is not supported with the PMD, since there is no physical backend device by default.

35.3. PMD arguments

no_request_thread, by default PMD creates a pthread for each KNI interface to handle Linux network interface control commands, like ifconfig kni0 up

With no_request_thread option, pthread is not created and control commands not handled by PMD.

By default request thread is enabled. And this argument should not be used most of the time, unless this PMD used with customized DPDK application to handle requests itself.

Argument usage:

dpdk-testpmd --vdev "net_kni0,no_request_thread=1" -- -i

35.4. PMD log messages

If KNI kernel module (rte_kni.ko) not inserted, following error log printed:

"KNI: KNI subsystem has not been initialized. Invoke rte_kni_init() first"

35.5. PMD testing

It is possible to test PMD quickly using KNI kernel module loopback feature:

  • Insert KNI kernel module with loopback support:

    insmod <build_dir>/kernel/linux/kni/rte_kni.ko lo_mode=lo_mode_fifo_skb

  • Start testpmd with no physical device but two KNI virtual devices:

    ./dpdk-testpmd --vdev net_kni0 --vdev net_kni1 -- -i

    ...
Configuring Port 0 (socket 0)
KNI: pci: 00:00:00       c580:b8
Port 0: 1A:4A:5B:7C:A2:8C
Configuring Port 1 (socket 0)
KNI: pci: 00:00:00       600:b9
Port 1: AE:95:21:07:93:DD
Checking link statuses...
Port 0 Link Up - speed 10000 Mbps - full-duplex
Port 1 Link Up - speed 10000 Mbps - full-duplex
Done
testpmd>

  • Observe Linux interfaces

    $ ifconfig kni0 && ifconfig kni1
kni0: flags=4098<BROADCAST,MULTICAST>  mtu 1500
        ether ae:8e:79:8e:9b:c8  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

kni1: flags=4098<BROADCAST,MULTICAST>  mtu 1500
        ether 9e:76:43:53:3e:9b  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

  • Start forwarding with tx_first:

    testpmd> start tx_first

  • Quit and check forwarding stats:

    testpmd> quit
Telling cores to stop...
Waiting for lcores to finish...

---------------------- Forward statistics for port 0  ----------------------
RX-packets: 35637905       RX-dropped: 0             RX-total: 35637905
TX-packets: 35637947       TX-dropped: 0             TX-total: 35637947
----------------------------------------------------------------------------

---------------------- Forward statistics for port 1  ----------------------
RX-packets: 35637915       RX-dropped: 0             RX-total: 35637915
TX-packets: 35637937       TX-dropped: 0             TX-total: 35637937
----------------------------------------------------------------------------

+++++++++++++++ Accumulated forward statistics for all ports+++++++++++++++
RX-packets: 71275820       RX-dropped: 0             RX-total: 71275820
TX-packets: 71275884       TX-dropped: 0             TX-total: 71275884
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++