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36 The DPDK Kernel NIC Interface (KNI) allows userspace applications access to the Linux* control plane.
38 The benefits of using the DPDK KNI are:
40 * Faster than existing Linux TUN/TAP interfaces
41 (by eliminating system calls and copy_to_user()/copy_from_user() operations.
43 * Allows management of DPDK ports using standard Linux net tools such as ethtool, ifconfig and tcpdump.
45 * Allows an interface with the kernel network stack.
47 The components of an application using the DPDK Kernel NIC Interface are shown in :numref:`figure_kernel_nic_intf`.
49 .. _figure_kernel_nic_intf:
51 .. figure:: img/kernel_nic_intf.*
53 Components of a DPDK KNI Application
56 The DPDK KNI Kernel Module
57 --------------------------
59 The KNI kernel loadable module provides support for two types of devices:
61 * A Miscellaneous device (/dev/kni) that:
63 * Creates net devices (via ioctl calls).
65 * Maintains a kernel thread context shared by all KNI instances
66 (simulating the RX side of the net driver).
68 * For single kernel thread mode, maintains a kernel thread context shared by all KNI instances
69 (simulating the RX side of the net driver).
71 * For multiple kernel thread mode, maintains a kernel thread context for each KNI instance
72 (simulating the RX side of the net driver).
76 * Net functionality provided by implementing several operations such as netdev_ops,
77 header_ops, ethtool_ops that are defined by struct net_device,
78 including support for DPDK mbufs and FIFOs.
80 * The interface name is provided from userspace.
82 * The MAC address can be the real NIC MAC address or random.
84 KNI Creation and Deletion
85 -------------------------
87 The KNI interfaces are created by a DPDK application dynamically.
88 The interface name and FIFO details are provided by the application through an ioctl call
89 using the rte_kni_device_info struct which contains:
93 * Physical addresses of the corresponding memzones for the relevant FIFOs.
95 * Mbuf mempool details, both physical and virtual (to calculate the offset for mbuf pointers).
101 Refer to rte_kni_common.h in the DPDK source code for more details.
103 The physical addresses will be re-mapped into the kernel address space and stored in separate KNI contexts.
105 The affinity of kernel RX thread (both single and multi-threaded modes) is controlled by force_bind and
106 core_id config parameters.
108 The KNI interfaces can be deleted by a DPDK application dynamically after being created.
109 Furthermore, all those KNI interfaces not deleted will be deleted on the release operation
110 of the miscellaneous device (when the DPDK application is closed).
115 To minimize the amount of DPDK code running in kernel space, the mbuf mempool is managed in userspace only.
116 The kernel module will be aware of mbufs,
117 but all mbuf allocation and free operations will be handled by the DPDK application only.
119 :numref:`figure_pkt_flow_kni` shows a typical scenario with packets sent in both directions.
121 .. _figure_pkt_flow_kni:
123 .. figure:: img/pkt_flow_kni.*
125 Packet Flow via mbufs in the DPDK KNI
131 On the DPDK RX side, the mbuf is allocated by the PMD in the RX thread context.
132 This thread will enqueue the mbuf in the rx_q FIFO.
133 The KNI thread will poll all KNI active devices for the rx_q.
134 If an mbuf is dequeued, it will be converted to a sk_buff and sent to the net stack via netif_rx().
135 The dequeued mbuf must be freed, so the same pointer is sent back in the free_q FIFO.
137 The RX thread, in the same main loop, polls this FIFO and frees the mbuf after dequeuing it.
142 For packet egress the DPDK application must first enqueue several mbufs to create an mbuf cache on the kernel side.
144 The packet is received from the Linux net stack, by calling the kni_net_tx() callback.
145 The mbuf is dequeued (without waiting due the cache) and filled with data from sk_buff.
146 The sk_buff is then freed and the mbuf sent in the tx_q FIFO.
148 The DPDK TX thread dequeues the mbuf and sends it to the PMD (via rte_eth_tx_burst()).
149 It then puts the mbuf back in the cache.
154 Ethtool is a Linux-specific tool with corresponding support in the kernel
155 where each net device must register its own callbacks for the supported operations.
156 The current implementation uses the igb/ixgbe modified Linux drivers for ethtool support.
157 Ethtool is not supported in i40e and VMs (VF or EM devices).
159 Link state and MTU change
160 -------------------------
162 Link state and MTU change are network interface specific operations usually done via ifconfig.
163 The request is initiated from the kernel side (in the context of the ifconfig process)
164 and handled by the user space DPDK application.
165 The application polls the request, calls the application handler and returns the response back into the kernel space.
167 The application handlers can be registered upon interface creation or explicitly registered/unregistered in runtime.
168 This provides flexibility in multiprocess scenarios
169 (where the KNI is created in the primary process but the callbacks are handled in the secondary one).
170 The constraint is that a single process can register and handle the requests.