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31 Poll Mode Driver for Emulated Virtio NIC
32 ========================================
34 Virtio is a para-virtualization framework initiated by IBM, and supported by KVM hypervisor.
35 In the Data Plane Development Kit (DPDK),
36 we provide a virtio Poll Mode Driver (PMD) as a software solution, comparing to SRIOV hardware solution,
37 for fast guest VM to guest VM communication and guest VM to host communication.
39 Vhost is a kernel acceleration module for virtio qemu backend.
40 The DPDK extends kni to support vhost raw socket interface,
41 which enables vhost to directly read/ write packets from/to a physical port.
42 With this enhancement, virtio could achieve quite promising performance.
44 In future release, we will also make enhancement to vhost backend,
45 releasing peak performance of virtio PMD driver.
47 For basic qemu-KVM installation and other Intel EM poll mode driver in guest VM,
48 please refer to Chapter "Driver for VM Emulated Devices".
50 In this chapter, we will demonstrate usage of virtio PMD driver with two backends,
51 standard qemu vhost back end and vhost kni back end.
53 Virtio Implementation in DPDK
54 -----------------------------
56 For details about the virtio spec, refer to Virtio PCI Card Specification written by Rusty Russell.
58 As a PMD, virtio provides packet reception and transmission callbacks virtio_recv_pkts and virtio_xmit_pkts.
60 In virtio_recv_pkts, index in range [vq->vq_used_cons_idx , vq->vq_ring.used->idx) in vring is available for virtio to burst out.
62 In virtio_xmit_pkts, same index range in vring is available for virtio to clean.
63 Virtio will enqueue to be transmitted packets into vring, advance the vq->vq_ring.avail->idx,
64 and then notify the host back end if necessary.
66 Features and Limitations of virtio PMD
67 --------------------------------------
69 In this release, the virtio PMD driver provides the basic functionality of packet reception and transmission.
71 * It supports merge-able buffers per packet when receiving packets and scattered buffer per packet
72 when transmitting packets. The packet size supported is from 64 to 1518.
74 * It supports multicast packets and promiscuous mode.
76 * The descriptor number for the RX/TX queue is hard-coded to be 256 by qemu.
77 If given a different descriptor number by the upper application,
78 the virtio PMD generates a warning and fall back to the hard-coded value.
80 * Features of mac/vlan filter are supported, negotiation with vhost/backend are needed to support them.
81 When backend can't support vlan filter, virtio app on guest should disable vlan filter to make sure
82 the virtio port is configured correctly. E.g. specify '--disable-hw-vlan' in testpmd command line.
84 * RTE_PKTMBUF_HEADROOM should be defined larger than sizeof(struct virtio_net_hdr), which is 10 bytes.
86 * Virtio does not support runtime configuration.
88 * Virtio supports Link State interrupt.
90 * Virtio supports software vlan stripping and inserting.
92 * Virtio supports using port IO to get PCI resource when uio/igb_uio module is not available.
97 The following prerequisites apply:
99 * In the BIOS, turn VT-x and VT-d on
101 * Linux kernel with KVM module; vhost module loaded and ioeventfd supported.
102 Qemu standard backend without vhost support isn't tested, and probably isn't supported.
104 Virtio with kni vhost Back End
105 ------------------------------
107 This section demonstrates kni vhost back end example setup for Phy-VM Communication.
109 .. _figure_host_vm_comms:
111 .. figure:: img/host_vm_comms.*
113 Host2VM Communication Example Using kni vhost Back End
116 Host2VM communication example
118 #. Load the kni kernel module:
120 .. code-block:: console
124 Other basic DPDK preparations like hugepage enabling, uio port binding are not listed here.
125 Please refer to the *DPDK Getting Started Guide* for detailed instructions.
127 #. Launch the kni user application:
129 .. code-block:: console
131 examples/kni/build/app/kni -c 0xf -n 4 -- -p 0x1 -i 0x1 -o 0x2
133 This command generates one network device vEth0 for physical port.
134 If specify more physical ports, the generated network device will be vEth1, vEth2, and so on.
136 For each physical port, kni creates two user threads.
137 One thread loops to fetch packets from the physical NIC port into the kni receive queue.
138 The other user thread loops to send packets in the kni transmit queue.
140 For each physical port, kni also creates a kernel thread that retrieves packets from the kni receive queue,
141 place them onto kni's raw socket's queue and wake up the vhost kernel thread to exchange packets with the virtio virt queue.
143 For more details about kni, please refer to Chapter 24 "Kernel NIC Interface".
145 #. Enable the kni raw socket functionality for the specified physical NIC port,
146 get the generated file descriptor and set it in the qemu command line parameter.
147 Always remember to set ioeventfd_on and vhost_on.
151 .. code-block:: console
153 echo 1 > /sys/class/net/vEth0/sock_en
154 fd=`cat /sys/class/net/vEth0/sock_fd`
155 exec qemu-system-x86_64 -enable-kvm -cpu host \
156 -m 2048 -smp 4 -name dpdk-test1-vm1 \
157 -drive file=/data/DPDKVMS/dpdk-vm.img \
158 -netdev tap, fd=$fd,id=mynet_kni, script=no,vhost=on \
159 -device virtio-net-pci,netdev=mynet_kni,bus=pci.0,addr=0x3,ioeventfd=on \
162 In the above example, virtio port 0 in the guest VM will be associated with vEth0, which in turns corresponds to a physical port,
163 which means received packets come from vEth0, and transmitted packets is sent to vEth0.
165 #. In the guest, bind the virtio device to the uio_pci_generic kernel module and start the forwarding application.
166 When the virtio port in guest bursts rx, it is getting packets from the raw socket's receive queue.
167 When the virtio port bursts tx, it is sending packet to the tx_q.
169 .. code-block:: console
172 echo 512 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
173 modprobe uio_pci_generic
174 python tools/dpdk_nic_bind.py -b uio_pci_generic 00:03.0
176 We use testpmd as the forwarding application in this example.
178 .. figure:: img/console.*
182 #. Use IXIA packet generator to inject a packet stream into the KNI physical port.
184 The packet reception and transmission flow path is:
186 IXIA packet generator->82599 PF->KNI rx queue->KNI raw socket queue->Guest VM virtio port 0 rx burst->Guest VM virtio port 0 tx burst-> KNI tx queue->82599 PF-> IXIA packet generator
188 Virtio with qemu virtio Back End
189 --------------------------------
191 .. _figure_host_vm_comms_qemu:
193 .. figure:: img/host_vm_comms_qemu.*
195 Host2VM Communication Example Using qemu vhost Back End
198 .. code-block:: console
200 qemu-system-x86_64 -enable-kvm -cpu host -m 2048 -smp 2 -mem-path /dev/
201 hugepages -mem-prealloc
202 -drive file=/data/DPDKVMS/dpdk-vm1
203 -netdev tap,id=vm1_p1,ifname=tap0,script=no,vhost=on
204 -device virtio-net-pci,netdev=vm1_p1,bus=pci.0,addr=0x3,ioeventfd=on
205 -device pci-assign,host=04:10.1 \
207 In this example, the packet reception flow path is:
209 IXIA packet generator->82599 PF->Linux Bridge->TAP0's socket queue-> Guest VM virtio port 0 rx burst-> Guest VM 82599 VF port1 tx burst-> IXIA packet generator
211 The packet transmission flow is:
213 IXIA packet generator-> Guest VM 82599 VF port1 rx burst-> Guest VM virtio port 0 tx burst-> tap -> Linux Bridge->82599 PF-> IXIA packet generator