DPDK vHost User Ports¶
The DPDK datapath provides DPDK-backed vHost user ports as a primary way to interact with guests. For more information on vHost User, refer to the QEMU documentation on same.
This example demonstrates how to add two
dpdkvhostuser ports to an existing
$ ovs-vsctl add-port br0 dpdkvhostuser0 \ -- set Interface dpdkvhostuser0 type=dpdkvhostuser $ ovs-vsctl add-port br0 dpdkvhostuser1 \ -- set Interface dpdkvhostuser1 type=dpdkvhostuser
vhost-user vs. vhost-user-client¶
Open vSwitch provides two types of vHost User ports:
- vhost-user (
- vhost-user-client (
vHost User uses a client-server model. The server creates/manages/destroys the
vHost User sockets, and the client connects to the server. Depending on which
port type you use,
dpdkvhostuserclient, a different
configuration of the client-server model is used.
For vhost-user ports, Open vSwitch acts as the server and QEMU the client. For vhost-user-client ports, Open vSwitch acts as the client and QEMU the server.
Use of vhost-user ports requires QEMU >= 2.2
To use vhost-user ports, you must first add said ports to the switch. Unlike
DPDK ring ports, DPDK vhost-user ports can have arbitrary names, except that
forward and backward slashes are prohibited in the names. For vhost-user, the
port type is
$ ovs-vsctl add-port br0 vhost-user-1 -- set Interface vhost-user-1 \ type=dpdkvhostuser
This action creates a socket located at
/usr/local/var/run/openvswitch/vhost-user-1, which you must provide to your
VM on the QEMU command line.
If you wish for the vhost-user sockets to be created in a sub-directory of
/usr/local/var/run/openvswitch, you may specify this directory in the
ovsdb like so:
$ ovs-vsctl --no-wait \ set Open_vSwitch . other_config:vhost-sock-dir=subdir`
Once the vhost-user ports have been added to the switch, they must be added to the guest. There are two ways to do this: using QEMU directly, or using libvirt.
Adding vhost-user ports to the guest (QEMU)¶
To begin, you must attach the vhost-user device sockets to the guest. To do this, you must pass the following parameters to QEMU:
-chardev socket,id=char1,path=/usr/local/var/run/openvswitch/vhost-user-1 -netdev type=vhost-user,id=mynet1,chardev=char1,vhostforce -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1
vhost-user-1 is the name of the vhost-user port added to the switch.
Repeat the above parameters for multiple devices, changing the chardev
id as necessary. Note that a separate and different chardev
needs to be specified for each vhost-user device. For example you have a second
vhost-user port named
vhost-user-2, you append your QEMU command line with
an additional set of parameters:
-chardev socket,id=char2,path=/usr/local/var/run/openvswitch/vhost-user-2 -netdev type=vhost-user,id=mynet2,chardev=char2,vhostforce -device virtio-net-pci,mac=00:00:00:00:00:02,netdev=mynet2
In addition, QEMU must allocate the VM’s memory on hugetlbfs. vhost-user ports access a virtio-net device’s virtual rings and packet buffers mapping the VM’s physical memory on hugetlbfs. To enable vhost-user ports to map the VM’s memory into their process address space, pass the following parameters to QEMU:
-object memory-backend-file,id=mem,size=4096M,mem-path=/dev/hugepages,share=on -numa node,memdev=mem -mem-prealloc
Finally, you may wish to enable multiqueue support. This is optional but, should you wish to enable it, run:
-chardev socket,id=char2,path=/usr/local/var/run/openvswitch/vhost-user-2 -netdev type=vhost-user,id=mynet2,chardev=char2,vhostforce,queues=$q -device virtio-net-pci,mac=00:00:00:00:00:02,netdev=mynet2,mq=on,vectors=$v
- The number of queues
- The number of vectors, which is
$q* 2 + 2
The vhost-user interface will be automatically reconfigured with required
number of rx and tx queues after connection of virtio device. Manual
n_rxq is not supported because OVS will work properly only
n_rxq will match number of queues configured in QEMU.
A least 2 PMDs should be configured for the vswitch when using multiqueue. Using a single PMD will cause traffic to be enqueued to the same vhost queue rather than being distributed among different vhost queues for a vhost-user interface.
If traffic destined for a VM configured with multiqueue arrives to the vswitch via a physical DPDK port, then the number of rxqs should also be set to at least 2 for that physical DPDK port. This is required to increase the probability that a different PMD will handle the multiqueue transmission to the guest using a different vhost queue.
If one wishes to use multiple queues for an interface in the guest, the driver
in the guest operating system must be configured to do so. It is recommended
that the number of queues configured be equal to
For example, this can be done for the Linux kernel virtio-net driver with:
$ ethtool -L <DEV> combined <$q>
- Changes the numbers of channels of the specified network device
- Changes the number of multi-purpose channels.
Adding vhost-user ports to the guest (libvirt)¶
To begin, you must change the user and group that libvirt runs under, configure access control policy and restart libvirtd.
/etc/libvirt/qemu.confadd/edit the following lines:
user = "root" group = "root"
Disable SELinux or set to permissive mode:
$ setenforce 0
Finally, restart the libvirtd process, For example, on Fedora:
$ systemctl restart libvirtd.service
Once complete, instantiate the VM. A sample XML configuration file is provided at the end of this file. Save this file, then create a VM using this file:
$ virsh create demovm.xml
Once created, you can connect to the guest console:
$ virsh console demovm
The demovm xml configuration is aimed at achieving out of box performance on VM. These enhancements include:
- The vcpus are pinned to the cores of the CPU socket 0 using
- Configure NUMA cell and memory shared using
Refer to the libvirt documentation for more information.
Use of vhost-user ports requires QEMU >= 2.7
To use vhost-user-client ports, you must first add said ports to the switch.
Like DPDK vhost-user ports, DPDK vhost-user-client ports can have mostly
arbitrary. However, the name given to the port does not govern the name of the
socket device. Instead, this must be configured by the user by way of a
vhost-server-path option. For vhost-user-client, the port type is
$ VHOST_USER_SOCKET_PATH=/path/to/socket $ ovs-vsctl add-port br0 vhost-client-1 \ -- set Interface vhost-client-1 type=dpdkvhostuserclient \ options:vhost-server-path=$VHOST_USER_SOCKET_PATH
Once the vhost-user-client ports have been added to the switch, they must be added to the guest. Like vhost-user ports, there are two ways to do this: using QEMU directly, or using libvirt. Only the QEMU case is covered here.
Adding vhost-user-client ports to the guest (QEMU)¶
Attach the vhost-user device sockets to the guest. To do this, you must pass the following parameters to QEMU:
-chardev socket,id=char1,path=$VHOST_USER_SOCKET_PATH,server -netdev type=vhost-user,id=mynet1,chardev=char1,vhostforce -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1
vhost-user-1 is the name of the vhost-user port added to the switch.
If the corresponding
dpdkvhostuserclient port has not yet been configured
in OVS with
vhost-server-path=/path/to/socket, QEMU will print a log
similar to the following:
QEMU waiting for connection on: disconnected:unix:/path/to/socket,server
QEMU will wait until the port is created sucessfully in OVS to boot the VM. One benefit of using this mode is the ability for vHost ports to ‘reconnect’ in event of the switch crashing or being brought down. Once it is brought back up, the vHost ports will reconnect automatically and normal service will resume.
DPDK in the Guest¶
testpmd application can be run in guest VMs for high speed packet
forwarding between vhostuser ports. DPDK and testpmd application has to be
compiled on the guest VM. Below are the steps for setting up the testpmd
application in the VM.
Support for DPDK in the guest requires QEMU >= 2.2
$ cd /root/dpdk/ $ wget http://fast.dpdk.org/rel/dpdk-16.11.tar.xz $ tar xf dpdk-16.11.tar.xz $ export DPDK_DIR=/root/dpdk/dpdk-16.11 $ export DPDK_TARGET=x86_64-native-linuxapp-gcc $ export DPDK_BUILD=$DPDK_DIR/$DPDK_TARGET $ cd $DPDK_DIR $ make install T=$DPDK_TARGET DESTDIR=install
Build the test-pmd application:
$ cd app/test-pmd $ export RTE_SDK=$DPDK_DIR $ export RTE_TARGET=$DPDK_TARGET $ make
Setup huge pages and DPDK devices using UIO:
$ sysctl vm.nr_hugepages=1024 $ mkdir -p /dev/hugepages $ mount -t hugetlbfs hugetlbfs /dev/hugepages # only if not already mounted $ modprobe uio $ insmod $DPDK_BUILD/kmod/igb_uio.ko $ $DPDK_DIR/tools/dpdk-devbind.py --status $ $DPDK_DIR/tools/dpdk-devbind.py -b igb_uio 00:03.0 00:04.0
vhost ports pci ids can be retrieved using:
lspci | grep Ethernet
Finally, start the application:
<domain type='kvm'> <name>demovm</name> <uuid>4a9b3f53-fa2a-47f3-a757-dd87720d9d1d</uuid> <memory unit='KiB'>4194304</memory> <currentMemory unit='KiB'>4194304</currentMemory> <memoryBacking> <hugepages> <page size='2' unit='M' nodeset='0'/> </hugepages> </memoryBacking> <vcpu placement='static'>2</vcpu> <cputune> <shares>4096</shares> <vcpupin vcpu='0' cpuset='4'/> <vcpupin vcpu='1' cpuset='5'/> <emulatorpin cpuset='4,5'/> </cputune> <os> <type arch='x86_64' machine='pc'>hvm</type> <boot dev='hd'/> </os> <features> <acpi/> <apic/> </feature> <cpu mode='host-model'> <model fallback='allow'/> <topology sockets='2' cores='1' threads='1'/> <numa> <cell id='0' cpus='0-1' memory='4194304' unit='KiB' memAccess='shared'/> </numa> </cpu> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>destroy</on_crash> <devices> <emulator>/usr/bin/qemu-kvm</emulator> <disk type='file' device='disk'> <driver name='qemu' type='qcow2' cache='none'/> <source file='/root/CentOS7_x86_64.qcow2'/> <target dev='vda' bus='virtio'/> </disk> <disk type='dir' device='disk'> <driver name='qemu' type='fat'/> <source dir='/usr/src/dpdk-16.11'/> <target dev='vdb' bus='virtio'/> <readonly/> </disk> <interface type='vhostuser'> <mac address='00:00:00:00:00:01'/> <source type='unix' path='/usr/local/var/run/openvswitch/dpdkvhostuser0' mode='client'/> <model type='virtio'/> <driver queues='2'> <host mrg_rxbuf='off'/> </driver> </interface> <interface type='vhostuser'> <mac address='00:00:00:00:00:02'/> <source type='unix' path='/usr/local/var/run/openvswitch/dpdkvhostuser1' mode='client'/> <model type='virtio'/> <driver queues='2'> <host mrg_rxbuf='off'/> </driver> </interface> <serial type='pty'> <target port='0'/> </serial> <console type='pty'> <target type='serial' port='0'/> </console> </devices> </domain>