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33 Vhost Sample Application
34 ========================
36 The vhost sample application demonstrates integration of the Data Plane
37 Development Kit (DPDK) with the Linux* KVM hypervisor by implementing the
38 vhost-net offload API. The sample application performs simple packet
39 switching between virtual machines based on Media Access Control (MAC)
40 address or Virtual Local Area Network (VLAN) tag. The splitting of Ethernet
41 traffic from an external switch is performed in hardware by the Virtual
42 Machine Device Queues (VMDQ) and Data Center Bridging (DCB) features of
43 the IntelĀ® 82599 10 Gigabit Ethernet Controller.
48 This section shows the steps how to test a typical PVP case with this
49 vhost-switch sample, whereas packets are received from the physical NIC
50 port first and enqueued to the VM's Rx queue. Through the guest testpmd's
51 default forwarding mode (io forward), those packets will be put into
52 the Tx queue. The vhost-switch example, in turn, gets the packets and
53 puts back to the same physical NIC port.
58 To compile the sample application see :doc:`compiling`.
60 The application is located in the ``vhost`` sub-directory.
63 In this example, you need build DPDK both on the host and inside guest.
65 Start the vswitch example
66 ~~~~~~~~~~~~~~~~~~~~~~~~~
68 .. code-block:: console
70 ./vhost-switch -l 0-3 -n 4 --socket-mem 1024 \
71 -- --socket-file /tmp/sock0 --client \
74 Check the `Parameters`_ section for the explanations on what do those
82 .. code-block:: console
84 qemu-system-x86_64 -machine accel=kvm -cpu host \
85 -m $mem -object memory-backend-file,id=mem,size=$mem,mem-path=/dev/hugepages,share=on \
86 -mem-prealloc -numa node,memdev=mem \
88 -chardev socket,id=char1,path=/tmp/sock0,server \
89 -netdev type=vhost-user,id=hostnet1,chardev=char1 \
90 -device virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:00:00:14 \
94 For basic vhost-user support, QEMU 2.2 (or above) is required. For
95 some specific features, a higher version might be need. Such as
96 QEMU 2.7 (or above) for the reconnect feature.
98 .. _vhost_app_run_dpdk_inside_guest:
100 Run testpmd inside guest
101 ~~~~~~~~~~~~~~~~~~~~~~~~
103 Make sure you have DPDK built inside the guest. Also make sure the
104 corresponding virtio-net PCI device is bond to a uio driver, which
107 .. code-block:: console
109 modprobe uio_pci_generic
110 $RTE_SDK/usertools/dpdk-devbind.py -b=uio_pci_generic 0000:00:04.0
112 Then start testpmd for packet forwarding testing.
114 .. code-block:: console
116 ./x86_64-native-gcc/app/testpmd -l 0-1 -- -i
122 While a virtio-net is connected to vhost-switch, a VLAN tag starts with
123 1000 is assigned to it. So make sure configure your packet generator
124 with the right MAC and VLAN tag, you should be able to see following
125 log from the vhost-switch console. It means you get it work::
127 VHOST_DATA: (0) mac 52:54:00:00:00:14 and vlan 1000 registered
130 .. _vhost_app_parameters:
135 **--socket-file path**
136 Specifies the vhost-user socket file path.
139 DPDK vhost-user will act as the client mode when such option is given.
140 In the client mode, QEMU will create the socket file. Otherwise, DPDK
141 will create it. Put simply, it's the server to create the socket file.
145 The vm2vm parameter sets the mode of packet switching between guests in
148 - 0 disables vm2vm, impling that VM's packets will always go to the NIC port.
149 - 1 means a normal mac lookup packet routing.
150 - 2 means hardware mode packet forwarding between guests, it allows packets
151 go to the NIC port, hardware L2 switch will determine which guest the
152 packet should forward to or need send to external, which bases on the
153 packet destination MAC address and VLAN tag.
156 Set 0/1 to disable/enable the mergeable Rx feature. It's disabled by default.
159 The stats parameter controls the printing of virtio-net device statistics.
160 The parameter specifies an interval (in unit of seconds) to print statistics,
161 with an interval of 0 seconds disabling statistics.
164 The rx-retry option enables/disables enqueue retries when the guests Rx queue
165 is full. This feature resolves a packet loss that is observed at high data
166 rates, by allowing it to delay and retry in the receive path. This option is
169 **--rx-retry-num num**
170 The rx-retry-num option specifies the number of retries on an Rx burst, it
171 takes effect only when rx retry is enabled. The default value is 4.
173 **--rx-retry-delay msec**
174 The rx-retry-delay option specifies the timeout (in micro seconds) between
175 retries on an RX burst, it takes effect only when rx retry is enabled. The
178 **--dequeue-zero-copy**
179 Dequeue zero copy will be enabled when this option is given.
182 VLAN strip option is removed, because different NICs have different behaviors
183 when disabling VLAN strip. Such feature, which heavily depends on hardware,
184 should be removed from this example to reduce confusion. Now, VLAN strip is
185 enabled and cannot be disabled.
190 * QEMU fails to allocate memory on hugetlbfs, with an error like the
193 file_ram_alloc: can't mmap RAM pages: Cannot allocate memory
195 When running QEMU the above error indicates that it has failed to allocate
196 memory for the Virtual Machine on the hugetlbfs. This is typically due to
197 insufficient hugepages being free to support the allocation request. The
198 number of free hugepages can be checked as follows:
200 .. code-block:: console
202 cat /sys/kernel/mm/hugepages/hugepages-<pagesize>/nr_hugepages
204 The command above indicates how many hugepages are free to support QEMU's
207 * vhost-user will not work with QEMU without the ``-mem-prealloc`` option
209 The current implementation works properly only when the guest memory is
212 * vhost-user will not work with a QEMU version without shared memory mapping:
214 Make sure ``share=on`` QEMU option is given.
216 * Failed to build DPDK in VM
218 Make sure "-cpu host" QEMU option is given.