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Using Open vSwitch with DPDK

Open vSwitch can use Intel(R) DPDK lib to operate entirely in userspace. This file explains how to install and use Open vSwitch in such a mode.

The DPDK support of Open vSwitch is considered experimental. It has not been thoroughly tested.

This version of Open vSwitch should be built manually with configure and make.

OVS needs a system with 1GB hugepages support.

Building and Installing:

Required DPDK 1.8.0, fuse, fuse-devel (libfuse-dev on Debian/Ubuntu)

  1. Configure build & install DPDK:

  2. Set $DPDK_DIR

    export DPDK_DIR=/usr/src/dpdk-1.8.0
cd $DPDK_DIR

  3. Update config/common_linuxapp so that DPDK generate single lib file. (modification also required for IVSHMEM build)

    CONFIG_RTE_BUILD_COMBINE_LIBS=y

    Update config/common_linuxapp so that DPDK is built with vhost libraries:

    CONFIG_RTE_LIBRTE_VHOST=y

    Then run make install to build and install the library. For default install without IVSHMEM:

    make install T=x86_64-native-linuxapp-gcc

    To include IVSHMEM (shared memory):

    make install T=x86_64-ivshmem-linuxapp-gcc

    For further details refer to http://dpdk.org/

  4. Configure & build the Linux kernel:

    Refer to intel-dpdk-getting-started-guide.pdf for understanding DPDK kernel requirement.

  5. Configure & build OVS:

    • Non IVSHMEM:

      export DPDK_BUILD=$DPDK_DIR/x86_64-native-linuxapp-gcc/

    • IVSHMEM:

      export DPDK_BUILD=$DPDK_DIR/x86_64-ivshmem-linuxapp-gcc/

    cd $(OVS_DIR)/openvswitch
./boot.sh
./configure --with-dpdk=$DPDK_BUILD
make

To have better performance one can enable aggressive compiler optimizations and use the special instructions(popcnt, crc32) that may not be available on all machines. Instead of typing make, type:

make CFLAGS='-O3 -march=native'

Refer to INSTALL.userspace.md for general requirements of building userspace OVS.

Using the DPDK with ovs-vswitchd:

  1. Setup system boot Add the following options to the kernel bootline:

    default_hugepagesz=1GB hugepagesz=1G hugepages=1

  2. Setup DPDK devices:

    DPDK devices can be setup using either the VFIO (for DPDK 1.7+) or UIO modules. UIO requires inserting an out of tree driver igb_uio.ko that is available in DPDK. Setup for both methods are described below.

    • UIO:

      1. insert uio.ko: modprobe uio
      2. insert igb_uio.ko: insmod $DPDK_BUILD/kmod/igb_uio.ko
      3. Bind network device to igb_uio: $DPDK_DIR/tools/dpdk_nic_bind.py --bind=igb_uio eth1

    • VFIO:

      VFIO needs to be supported in the kernel and the BIOS. More information can be found in the DPDK Linux GSG.

      1. Insert vfio-pci.ko: modprobe vfio-pci
      2. Set correct permissions on vfio device: sudo /usr/bin/chmod a+x /dev/vfio and: sudo /usr/bin/chmod 0666 /dev/vfio/*
      3. Bind network device to vfio-pci: $DPDK_DIR/tools/dpdk_nic_bind.py --bind=vfio-pci eth1

  3. Mount the hugetable filsystem

    mount -t hugetlbfs -o pagesize=1G none /dev/hugepages

    Ref to http://www.dpdk.org/doc/quick-start for verifying DPDK setup.

  4. Follow the instructions in INSTALL.md to install only the userspace daemons and utilities (via 'make install').

    1. First time only db creation (or clearing):

      mkdir -p /usr/local/etc/openvswitch
mkdir -p /usr/local/var/run/openvswitch
rm /usr/local/etc/openvswitch/conf.db
ovsdb-tool create /usr/local/etc/openvswitch/conf.db  \
       /usr/local/share/openvswitch/vswitch.ovsschema

    2. Start ovsdb-server

      ovsdb-server --remote=punix:/usr/local/var/run/openvswitch/db.sock \
    --remote=db:Open_vSwitch,Open_vSwitch,manager_options \
    --private-key=db:Open_vSwitch,SSL,private_key \
    --certificate=Open_vSwitch,SSL,certificate \
    --bootstrap-ca-cert=db:Open_vSwitch,SSL,ca_cert --pidfile --detach

    3. First time after db creation, initialize:

      ovs-vsctl --no-wait init

  5. Start vswitchd:

    DPDK configuration arguments can be passed to vswitchd via --dpdk argument. This needs to be first argument passed to vswitchd process. dpdk arg -c is ignored by ovs-dpdk, but it is a required parameter for dpdk initialization.

    export DB_SOCK=/usr/local/var/run/openvswitch/db.sock
ovs-vswitchd --dpdk -c 0x1 -n 4 -- unix:$DB_SOCK --pidfile --detach

    If allocated more than one GB hugepage (as for IVSHMEM), set amount and use NUMA node 0 memory:

    ovs-vswitchd --dpdk -c 0x1 -n 4 --socket-mem 1024,0 \
-- unix:$DB_SOCK --pidfile --detach

  6. Add bridge & ports

    To use ovs-vswitchd with DPDK, create a bridge with datapath_type "netdev" in the configuration database. For example:

    ovs-vsctl add-br br0 -- set bridge br0 datapath_type=netdev

    Now you can add dpdk devices. OVS expect DPDK device name start with dpdk and end with portid. vswitchd should print (in the log file) the number of dpdk devices found.

    ovs-vsctl add-port br0 dpdk0 -- set Interface dpdk0 type=dpdk
ovs-vsctl add-port br0 dpdk1 -- set Interface dpdk1 type=dpdk

    Once first DPDK port is added to vswitchd, it creates a Polling thread and polls dpdk device in continuous loop. Therefore CPU utilization for that thread is always 100%.

  7. Add test flows

    Test flow script across NICs (assuming ovs in /usr/src/ovs): Execute script:

    #! /bin/sh
# Move to command directory
cd /usr/src/ovs/utilities/

# Clear current flows
./ovs-ofctl del-flows br0

# Add flows between port 1 (dpdk0) to port 2 (dpdk1)
./ovs-ofctl add-flow br0 in_port=1,action=output:2
./ovs-ofctl add-flow br0 in_port=2,action=output:1

  8. Performance tuning

    With pmd multi-threading support, OVS creates one pmd thread for each numa node as default. The pmd thread handles the I/O of all DPDK interfaces on the same numa node. The following two commands can be used to configure the multi-threading behavior.

    ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=<hex string>

    The command above asks for a CPU mask for setting the affinity of pmd threads. A set bit in the mask means a pmd thread is created and pinned to the corresponding CPU core. For more information, please refer to man ovs-vswitchd.conf.db

    ovs-vsctl set Open_vSwitch . other_config:n-dpdk-rxqs=<integer>

    The command above sets the number of rx queues of each DPDK interface. The rx queues are assigned to pmd threads on the same numa node in round-robin fashion. For more information, please refer to man ovs-vswitchd.conf.db

    Ideally for maximum throughput, the pmd thread should not be scheduled out which temporarily halts its execution. The following affinitization methods can help.

    Lets pick core 4,6,8,10 for pmd threads to run on. Also assume a dual 8 core sandy bridge system with hyperthreading enabled where CPU1 has cores 0,...,7 and 16,...,23 & CPU2 cores 8,...,15 & 24,...,31. (A different cpu configuration could have different core mask requirements).

    To kernel bootline add core isolation list for cores and associated hype cores (e.g. isolcpus=4,20,6,22,8,24,10,26,). Reboot system for isolation to take effect, restart everything.

    Configure pmd threads on core 4,6,8,10 using 'pmd-cpu-mask':

    ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=00000550

    You should be able to check that pmd threads are pinned to the correct cores via:

    top -p `pidof ovs-vswitchd` -H -d1

    Note, the pmd threads on a numa node are only created if there is at least one DPDK interface from the numa node that has been added to OVS.

    Note, core 0 is always reserved from non-pmd threads and should never be set in the cpu mask.

    To understand where most of the time is spent and whether the caches are effective, these commands can be used:

    ovs-appctl dpif-netdev/pmd-stats-clear #To reset statistics
ovs-appctl dpif-netdev/pmd-stats-show

DPDK Rings :

Following the steps above to create a bridge, you can now add dpdk rings as a port to the vswitch. OVS will expect the DPDK ring device name to start with dpdkr and end with a portid.

ovs-vsctl add-port br0 dpdkr0 -- set Interface dpdkr0 type=dpdkr

DPDK rings client test application

Included in the test directory is a sample DPDK application for testing the rings. This is from the base dpdk directory and modified to work with the ring naming used within ovs.

location tests/ovs_client

To run the client :

cd /usr/src/ovs/tests/
ovsclient -c 1 -n 4 --proc-type=secondary -- -n "port id you gave dpdkr"

In the case of the dpdkr example above the "port id you gave dpdkr" is 0.

It is essential to have --proc-type=secondary

The application simply receives an mbuf on the receive queue of the ethernet ring and then places that same mbuf on the transmit ring of the ethernet ring. It is a trivial loopback application.

DPDK rings in VM (IVSHMEM shared memory communications)

In addition to executing the client in the host, you can execute it within a guest VM. To do so you will need a patched qemu. You can download the patch and getting started guide at :

https://01.org/packet-processing/downloads

A general rule of thumb for better performance is that the client application should not be assigned the same dpdk core mask "-c" as the vswitchd.

DPDK vhost:

vhost-cuse is only supported at present i.e. not using the standard QEMU vhost-user interface. It is intended that vhost-user support will be added in future releases when supported in DPDK and that vhost-cuse will eventually be deprecated. See DPDK Docs for more info on vhost.

Prerequisites:

  1. Insert the Cuse module:

    modprobe cuse

  2. Build and insert the eventfd_link module:

    cd $DPDK_DIR/lib/librte_vhost/eventfd_link/ make insmod $DPDK_DIR/lib/librte_vhost/eventfd_link.ko

Following the steps above to create a bridge, you can now add DPDK vhost as a port to the vswitch.

ovs-vsctl add-port br0 dpdkvhost0 -- set Interface dpdkvhost0 type=dpdkvhost

Unlike DPDK ring ports, DPDK vhost ports can have arbitrary names:

ovs-vsctl add-port br0 port123ABC -- set Interface port123ABC type=dpdkvhost

However, please note that when attaching userspace devices to QEMU, the name provided during the add-port operation must match the ifname parameter on the QEMU command line.

DPDK vhost VM configuration:

vhost ports use a Linux* character device to communicate with QEMU. By default it is set to /dev/vhost-net. It is possible to reuse this standard device for DPDK vhost, which makes setup a little simpler but it is better practice to specify an alternative character device in order to avoid any conflicts if kernel vhost is to be used in parallel.

  1. This step is only needed if using an alternative character device.

    The new character device filename must be specified on the vswitchd commandline:

     `./vswitchd/ovs-vswitchd --dpdk --cuse_dev_name my-vhost-net -c 0x1 ...`

    Note that the --cuse_dev_name argument and associated string must be the first arguments after --dpdk and come before the EAL arguments. In the example above, the character device to be used will be /dev/my-vhost-net.

  2. This step is only needed if reusing the standard character device. It will conflict with the kernel vhost character device so the user must first remove it.

    `rm -rf /dev/vhost-net`

3a. Configure virtio-net adaptors: The following parameters must be passed to the QEMU binary:

 ```
 -netdev tap,id=<id>,script=no,downscript=no,ifname=<name>,vhost=on
 -device virtio-net-pci,netdev=net1,mac=<mac>
 ```

 Repeat the above parameters for multiple devices.

 The DPDK vhost library will negiotiate its own features, so they
 need not be passed in as command line params. Note that as offloads are
 disabled this is the equivalent of setting:

 `csum=off,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off`

3b. If using an alternative character device. It must be also explicitly passed to QEMU using the vhostfd argument:

 ```
 -netdev tap,id=<id>,script=no,downscript=no,ifname=<name>,vhost=on,
 vhostfd=<open_fd>
 -device virtio-net-pci,netdev=net1,mac=<mac>
 ```

 The open file descriptor must be passed to QEMU running as a child
 process. This could be done with a simple python script.

   ```
   #!/usr/bin/python
   fd = os.open("/dev/usvhost", os.O_RDWR)
   subprocess.call("qemu-system-x86_64 .... -netdev tap,id=vhostnet0,\
                    vhost=on,vhostfd=" + fd +"...", shell=True)

Alternatively the the qemu-wrap.py script can be used to automate the requirements specified above and can be used in conjunction with libvirt if desired. See the "DPDK vhost VM configuration with QEMU wrapper" section below.

  1. Configure huge pages: QEMU must allocate the VM's memory on hugetlbfs. Vhost ports access a virtio-net device's virtual rings and packet buffers mapping the VM's physical memory on hugetlbfs. To enable vhost-ports to map the VM's memory into their process address space, pass the following paramters to QEMU:

    -object memory-backend-file,id=mem,size=4096M,mem-path=/dev/hugepages, share=on -numa node,memdev=mem -mem-prealloc

DPDK vhost VM configuration with QEMU wrapper:

The QEMU wrapper script automatically detects and calls QEMU with the necessary parameters. It performs the following actions:

  • Automatically detects the location of the hugetlbfs and inserts this into the command line parameters.
  • Automatically open file descriptors for each virtio-net device and inserts this into the command line parameters.
  • Calls QEMU passing both the command line parameters passed to the script itself and those it has auto-detected.

Before use, you must edit the configuration parameters section of the script to point to the correct emulator location and set additional settings. Of these settings, emul_path and us_vhost_path must be set. All other settings are optional.

To use directly from the command line simply pass the wrapper some of the QEMU parameters: it will configure the rest. For example:

qemu-wrap.py -cpu host -boot c -hda <disk image> -m 4096 -smp 4
  --enable-kvm -nographic -vnc none -net none -netdev tap,id=net1,
  script=no,downscript=no,ifname=if1,vhost=on -device virtio-net-pci,
  netdev=net1,mac=00:00:00:00:00:01

DPDK vhost VM configuration with libvirt:

If you are using libvirt, you must enable libvirt to access the character device by adding it to controllers cgroup for libvirtd using the following steps.

 1. In `/etc/libvirt/qemu.conf` add/edit the following lines:

    ```
    1) clear_emulator_capabilities = 0
    2) user = "root"
    3) group = "root"
    4) cgroup_device_acl = [
           "/dev/null", "/dev/full", "/dev/zero",
           "/dev/random", "/dev/urandom",
           "/dev/ptmx", "/dev/kvm", "/dev/kqemu",
           "/dev/rtc", "/dev/hpet", "/dev/net/tun",
           "/dev/<my-vhost-device>",
           "/dev/hugepages"]
    ```

    <my-vhost-device> refers to "vhost-net" if using the `/dev/vhost-net`
    device. If you have specificed a different name on the ovs-vswitchd
    commandline using the "--cuse_dev_name" parameter, please specify that
    filename instead.

 2. Disable SELinux or set to permissive mode

 3. Restart the libvirtd process
    For example, on Fedora:

      `systemctl restart libvirtd.service`

After successfully editing the configuration, you may launch your vhost-enabled VM. The XML describing the VM can be configured like so within the qemu:commandline section:

 1. Set up shared hugepages:

 ```
 <qemu:arg value='-object'/>
 <qemu:arg value='memory-backend-file,id=mem,size=4096M,mem-path=/dev/hugepages,share=on'/>
 <qemu:arg value='-numa'/>
 <qemu:arg value='node,memdev=mem'/>
 <qemu:arg value='-mem-prealloc'/>
 ```

 2. Set up your tap devices:

 ```
 <qemu:arg value='-netdev'/>
 <qemu:arg value='type=tap,id=net1,script=no,downscript=no,ifname=vhost0,vhost=on'/>
 <qemu:arg value='-device'/>
 <qemu:arg value='virtio-net-pci,netdev=net1,mac=00:00:00:00:00:01'/>
 ```

 Repeat for as many devices as are desired, modifying the id, ifname
 and mac as necessary.

 Again, if you are using an alternative character device (other than
 `/dev/vhost-net`), please specify the file descriptor like so:

 `<qemu:arg value='type=tap,id=net3,script=no,downscript=no,ifname=vhost0,vhost=on,vhostfd=<open_fd>'/>`

 Where <open_fd> refers to the open file descriptor of the character device.
 Instructions of how to retrieve the file descriptor can be found in the
 "DPDK vhost VM configuration" section.
 Alternatively, the process is automated with the qemu-wrap.py script,
 detailed in the next section.

Now you may launch your VM using virt-manager, or like so:

`virsh create my_vhost_vm.xml`

DPDK vhost VM configuration with libvirt and QEMU wrapper:

To use the qemu-wrapper script in conjuntion with libvirt, follow the steps in the previous section before proceeding with the following steps:

  1. Place qemu-wrap.py in libvirtd's binary search PATH ($PATH) Ideally in the same directory that the QEMU binary is located.

  2. Ensure that the script has the same owner/group and file permissions as the QEMU binary.

  3. Update the VM xml file using "virsh edit VM.xml"

    1. Set the VM to use the launch script. Set the emulator path contained in the <emulator><emulator/> tags. For example, replace:

      <emulator>/usr/bin/qemu-kvm<emulator/>

      with:

      <emulator>/usr/bin/qemu-wrap.py<emulator/>

  4. Edit the Configuration Parameters section of the script to point to the correct emulator location and set any additional options. If you are using a alternative character device name, please set "us_vhost_path" to the location of that device. The script will automatically detect and insert the correct "vhostfd" value in the QEMU command line arguements.

  5. Use virt-manager to launch the VM

Restrictions:

  • Work with 1500 MTU, needs few changes in DPDK lib to fix this issue.
  • Currently DPDK port does not make use any offload functionality.
  • DPDK-vHost support works with 1G huge pages.

ivshmem:

  • The shared memory is currently restricted to the use of a 1GB huge pages.
  • All huge pages are shared amongst the host, clients, virtual machines etc.

Bug Reporting:

Please report problems to [email protected].