Open vSwitch with DPDK (Advanced)

The Advanced Install Guide explains how to improve OVS performance when using DPDK datapath. This guide provides information on tuning, system configuration, troubleshooting, static code analysis and testcases.

Building as a Shared Library

DPDK can be built as a static or a shared library and shall be linked by applications using DPDK datapath. When building OVS with DPDK, you can link Open vSwitch against the shared DPDK library.

Note

Minor performance loss is seen with OVS when using shared DPDK library as compared to static library.

To build Open vSwitch using DPDK as a shared library, first refer to the DPDK installation guide for download instructions for DPDK and OVS.

Once DPDK and OVS have been downloaded, you must configure the DPDK library accordingly. Simply set CONFIG_RTE_BUILD_SHARED_LIB=y in config/common_base, then build and install DPDK. Once done, DPDK can be built as usual. For example:

$ export DPDK_TARGET=x86_64-native-linuxapp-gcc
$ export DPDK_BUILD=$DPDK_DIR/$DPDK_TARGET
$ make install T=$DPDK_TARGET DESTDIR=install

Once DPDK is built, export the DPDK shared library location and setup OVS as detailed in the DPDK installation guide:

$ export LD_LIBRARY_PATH=$DPDK_DIR/x86_64-native-linuxapp-gcc/lib

System Configuration

To achieve optimal OVS performance, the system can be configured and that includes BIOS tweaks, Grub cmdline additions, better understanding of NUMA nodes and apt selection of PCIe slots for NIC placement.

Recommended BIOS Settings

Setting	Value
C3 Power State	Disabled
C6 Power State	Disabled
MLC Streamer	Enabled
MLC Spacial Prefetcher	Enabled
DCU Data Prefetcher	Enabled
DCA	Enabled
CPU Power and Performance	Performance
Memeory RAS and Performance Config -> NUMA optimized	Enabled

PCIe Slot Selection

The fastpath performance can be affected by factors related to the placement of the NIC, such as channel speeds between PCIe slot and CPU or the proximity of PCIe slot to the CPU cores running the DPDK application. Listed below are the steps to identify right PCIe slot.

Retrieve host details using dmidecode. For example:
```
$ dmidecode -t baseboard | grep "Product Name"
```
Download the technical specification for product listed, e.g: S2600WT2
Check the Product Architecture Overview on the Riser slot placement, CPU sharing info and also PCIe channel speeds

For example: On S2600WT, CPU1 and CPU2 share Riser Slot 1 with Channel speed between CPU1 and Riser Slot1 at 32GB/s, CPU2 and Riser Slot1 at 16GB/s. Running DPDK app on CPU1 cores and NIC inserted in to Riser card Slots will optimize OVS performance in this case.
Check the Riser Card #1 - Root Port mapping information, on the available slots and individual bus speeds. In S2600WT slot 1, slot 2 has high bus speeds and are potential slots for NIC placement.

Advanced Hugepage Setup

Allocate and mount 1 GB hugepages.

For persistent allocation of huge pages, add the following options to the kernel bootline:
```
default_hugepagesz=1GB hugepagesz=1G hugepages=N
```
For platforms supporting multiple huge page sizes, add multiple options:
```
default_hugepagesz=<size> hugepagesz=<size> hugepages=N
```
where:

N

number of huge pages requested

size

huge page size with an optional suffix [kKmMgG]
For run-time allocation of huge pages:
```
$ echo N > /sys/devices/system/node/nodeX/hugepages/hugepages-1048576kB/nr_hugepages
```
where:

N

number of huge pages requested

X

NUMA Node

Note

For run-time allocation of 1G huge pages, Contiguous Memory Allocator (CONFIG_CMA) has to be supported by kernel, check your Linux distro.

Now mount the huge pages, if not already done so:

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

Enable HyperThreading

With HyperThreading, or SMT, enabled, a physical core appears as two logical cores. SMT can be utilized to spawn worker threads on logical cores of the same physical core there by saving additional cores.

With DPDK, when pinning pmd threads to logical cores, care must be taken to set the correct bits of the pmd-cpu-mask to ensure that the pmd threads are pinned to SMT siblings.

Take a sample system configuration, with 2 sockets, 2 * 10 core processors, HT enabled. This gives us a total of 40 logical cores. To identify the physical core shared by two logical cores, run:

$ cat /sys/devices/system/cpu/cpuN/topology/thread_siblings_list

where N is the logical core number.

In this example, it would show that cores 1 and 21 share the same physical core., thus, the pmd-cpu-mask can be used to enable these two pmd threads running on these two logical cores (one physical core) is:

$ ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=100002

Isolate Cores

The isolcpus option can be used to isolate cores from the Linux scheduler. The isolated cores can then be used to dedicatedly run HPC applications or threads. This helps in better application performance due to zero context switching and minimal cache thrashing. To run platform logic on core 0 and isolate cores between 1 and 19 from scheduler, add isolcpus=1-19 to GRUB cmdline.

Note

It has been verified that core isolation has minimal advantage due to mature Linux scheduler in some circumstances.

NUMA/Cluster-on-Die

Ideally inter-NUMA datapaths should be avoided where possible as packets will go across QPI and there may be a slight performance penalty when compared with intra NUMA datapaths. On Intel Xeon Processor E5 v3, Cluster On Die is introduced on models that have 10 cores or more. This makes it possible to logically split a socket into two NUMA regions and again it is preferred where possible to keep critical datapaths within the one cluster.

It is good practice to ensure that threads that are in the datapath are pinned to cores in the same NUMA area. e.g. pmd threads and QEMU vCPUs responsible for forwarding. If DPDK is built with CONFIG_RTE_LIBRTE_VHOST_NUMA=y, vHost User ports automatically detect the NUMA socket of the QEMU vCPUs and will be serviced by a PMD from the same node provided a core on this node is enabled in the pmd-cpu-mask. libnuma packages are required for this feature.

Compiler Optimizations

The default compiler optimization level is -O2. Changing this to more aggressive compiler optimization such as -O3 -march=native with gcc (verified on 5.3.1) can produce performance gains though not siginificant. -march=native will produce optimized code on local machine and should be used when software compilation is done on Testbed.

Performance Tuning

Affinity

For superior performance, DPDK pmd threads and Qemu vCPU threads needs to be affinitized accordingly.

PMD thread Affinity

A poll mode driver (pmd) thread handles the I/O of all DPDK interfaces assigned to it. A pmd thread shall poll the ports for incoming packets, switch the packets and send to tx port. pmd thread is CPU bound, and needs to be affinitized to isolated cores for optimum performance.

By setting a bit in the mask, a pmd thread is created and pinned to the corresponding CPU core. e.g. to run a pmd thread on core 2:
```
$ ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=4
```
Note

pmd thread on a NUMA node is only created if there is at least one DPDK interface from that NUMA node added to OVS.
QEMU vCPU thread Affinity

A VM performing simple packet forwarding or running complex packet pipelines has to ensure that the vCPU threads performing the work has as much CPU occupancy as possible.

For example, on a multicore VM, multiple QEMU vCPU threads shall be spawned. When the DPDK testpmd application that does packet forwarding is invoked, the taskset command should be used to affinitize the vCPU threads to the dedicated isolated cores on the host system.

Multiple Poll-Mode Driver Threads

With pmd multi-threading support, OVS creates one pmd thread for each NUMA node by default. However, in cases where there are multiple ports/rxq's producing traffic, performance can be improved by creating multiple pmd threads running on separate cores. These pmd threads can share the workload by each being responsible for different ports/rxq's. Assignment of ports/rxq's to pmd threads is done automatically.

A set bit in the mask means a pmd thread is created and pinned to the corresponding CPU core. For example, to run pmd threads on core 1 and 2:

$ ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=6

When using dpdk and dpdkvhostuser ports in a bi-directional VM loopback as shown below, spreading the workload over 2 or 4 pmd threads shows significant improvements as there will be more total CPU occupancy available:

NIC port0 <-> OVS <-> VM <-> OVS <-> NIC port 1

DPDK Physical Port Rx Queues

$ ovs-vsctl set Interface <DPDK interface> options:n_rxq=<integer>

The command above sets the number of rx queues for DPDK physical interface. The rx queues are assigned to pmd threads on the same NUMA node in a round-robin fashion.

DPDK Physical Port Queue Sizes

$ ovs-vsctl set Interface dpdk0 options:n_rxq_desc=<integer>
$ ovs-vsctl set Interface dpdk0 options:n_txq_desc=<integer>

The command above sets the number of rx/tx descriptors that the NIC associated with dpdk0 will be initialised with.

Different n_rxq_desc and n_txq_desc configurations yield different benefits in terms of throughput and latency for different scenarios. Generally, smaller queue sizes can have a positive impact for latency at the expense of throughput. The opposite is often true for larger queue sizes. Note: increasing the number of rx descriptors eg. to 4096 may have a negative impact on performance due to the fact that non-vectorised DPDK rx functions may be used. This is dependant on the driver in use, but is true for the commonly used i40e and ixgbe DPDK drivers.

Exact Match Cache

Each pmd thread contains one Exact Match Cache (EMC). After initial flow setup in the datapath, the EMC contains a single table and provides the lowest level (fastest) switching for DPDK ports. If there is a miss in the EMC then the next level where switching will occur is the datapath classifier. Missing in the EMC and looking up in the datapath classifier incurs a significant performance penalty. If lookup misses occur in the EMC because it is too small to handle the number of flows, its size can be increased. The EMC size can be modified by editing the define EM_FLOW_HASH_SHIFT in lib/dpif-netdev.c.

As mentioned above, an EMC is per pmd thread. An alternative way of increasing the aggregate amount of possible flow entries in EMC and avoiding datapath classifier lookups is to have multiple pmd threads running.

Rx Mergeable Buffers

Rx mergeable buffers is a virtio feature that allows chaining of multiple virtio descriptors to handle large packet sizes. Large packets are handled by reserving and chaining multiple free descriptors together. Mergeable buffer support is negotiated between the virtio driver and virtio device and is supported by the DPDK vhost library. This behavior is supported and enabled by default, however in the case where the user knows that rx mergeable buffers are not needed i.e. jumbo frames are not needed, it can be forced off by adding mrg_rxbuf=off to the QEMU command line options. By not reserving multiple chains of descriptors it will make more individual virtio descriptors available for rx to the guest using dpdkvhost ports and this can improve performance.

OVS Testcases

PHY-VM-PHY (vHost Loopback)

The DPDK installation guide details steps for PHY-VM-PHY loopback testcase and packet forwarding using DPDK testpmd application in the Guest VM. For users wishing to do packet forwarding using kernel stack below, you need to run the below commands on the guest:

$ ifconfig eth1 1.1.1.2/24
$ ifconfig eth2 1.1.2.2/24
$ systemctl stop firewalld.service
$ systemctl stop iptables.service
$ sysctl -w net.ipv4.ip_forward=1
$ sysctl -w net.ipv4.conf.all.rp_filter=0
$ sysctl -w net.ipv4.conf.eth1.rp_filter=0
$ sysctl -w net.ipv4.conf.eth2.rp_filter=0
$ route add -net 1.1.2.0/24 eth2
$ route add -net 1.1.1.0/24 eth1
$ arp -s 1.1.2.99 DE:AD:BE:EF:CA:FE
$ arp -s 1.1.1.99 DE:AD:BE:EF:CA:EE

PHY-VM-PHY (IVSHMEM)

IVSHMEM can also be validated using the PHY-VM-PHY configuration. To begin, follow the steps described in the DPDK installation guide to create and initialize the database, start ovs-vswitchd and add dpdk-type devices to bridge br0. Once complete, follow the below steps:

Add DPDK ring port to the bridge:

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

Build modified QEMU

QEMU must be patched to enable IVSHMEM support:

$ cd /usr/src/
$ wget http://wiki.qemu.org/download/qemu-2.2.1.tar.bz2
$ tar -jxvf qemu-2.2.1.tar.bz2
$ cd /usr/src/qemu-2.2.1
$ wget https://raw.githubusercontent.com/netgroup-polito/un-orchestrator/master/orchestrator/compute_controller/plugins/kvm-libvirt/patches/ivshmem-qemu-2.2.1.patch
$ patch -p1 < ivshmem-qemu-2.2.1.patch
$ ./configure --target-list=x86_64-softmmu --enable-debug --extra-cflags='-g'
$ make -j 4

Generate QEMU commandline:

$ mkdir -p /usr/src/cmdline_generator
$ cd /usr/src/cmdline_generator
$ wget https://raw.githubusercontent.com/netgroup-polito/un-orchestrator/master/orchestrator/compute_controller/plugins/kvm-libvirt/cmdline_generator/cmdline_generator.c
$ wget https://raw.githubusercontent.com/netgroup-polito/un-orchestrator/master/orchestrator/compute_controller/plugins/kvm-libvirt/cmdline_generator/Makefile
$ export RTE_SDK=/usr/src/dpdk-16.11
$ export RTE_TARGET=x86_64-ivshmem-linuxapp-gcc
$ make
$ ./build/cmdline_generator -m -p dpdkr0 XXX
$ cmdline=`cat OVSMEMPOOL`

Start guest VM:

$ export VM_NAME=ivshmem-vm
$ export QCOW2_IMAGE=/root/CentOS7_x86_64.qcow2
$ export QEMU_BIN=/usr/src/qemu-2.2.1/x86_64-softmmu/qemu-system-x86_64
$ taskset 0x20 $QEMU_BIN -cpu host -smp 2,cores=2 -hda $QCOW2_IMAGE \
    -m 4096 --enable-kvm -name $VM_NAME -nographic -vnc :2 \
    -pidfile /tmp/vm1.pid $cmdline

Build and run the sample dpdkr app in VM:

$ echo 1024 > /proc/sys/vm/nr_hugepages
$ mount -t hugetlbfs nodev /dev/hugepages (if not already mounted)

# Build the DPDK ring application in the VM
$ export RTE_SDK=/root/dpdk-16.11
$ export RTE_TARGET=x86_64-ivshmem-linuxapp-gcc
$ make

# Run dpdkring application
$ ./build/dpdkr -c 1 -n 4 -- -n 0
# where "-n 0" refers to ring '0' i.e dpdkr0

PHY-VM-PHY (vHost Multiqueue)

vHost Multique functionality can also be validated using the PHY-VM-PHY configuration. To begin, follow the steps described in the DPDK installation guide to create and initialize the database, start ovs-vswitchd and add dpdk-type devices to bridge br0. Once complete, follow the below steps:

Configure PMD and RXQs.

For example, set the number of dpdk port rx queues to at least 2 The number of rx queues at vhost-user interface gets automatically configured after virtio device connection and doesn't need manual configuration:
```
$ ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=c
$ ovs-vsctl set Interface dpdk0 options:n_rxq=2
$ ovs-vsctl set Interface dpdk1 options:n_rxq=2
```

Instantiate Guest VM using QEMU cmdline

We must configure with appropriate software versions to ensure this feature is supported.

Recommended BIOS Settings

Setting	Value
QEMU version	2.5.0
QEMU thread affinity	2 cores (taskset 0x30)
Memory	4 GB
Cores	2
Distro	Fedora 22
Multiqueue	Enabled

To do this, instantiate the guest as follows:

$ export VM_NAME=vhost-vm
$ export GUEST_MEM=4096M
$ export QCOW2_IMAGE=/root/Fedora22_x86_64.qcow2
$ export VHOST_SOCK_DIR=/usr/local/var/run/openvswitch
$ taskset 0x30 qemu-system-x86_64 -cpu host -smp 2,cores=2 -m 4096M \
    -drive file=$QCOW2_IMAGE --enable-kvm -name $VM_NAME \
    -nographic -numa node,memdev=mem -mem-prealloc \
    -object memory-backend-file,id=mem,size=$GUEST_MEM,mem-path=/dev/hugepages,share=on \
    -chardev socket,id=char1,path=$VHOST_SOCK_DIR/dpdkvhostuser0 \
    -netdev type=vhost-user,id=mynet1,chardev=char1,vhostforce,queues=2 \
    -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,mq=on,vectors=6 \
    -chardev socket,id=char2,path=$VHOST_SOCK_DIR/dpdkvhostuser1 \
    -netdev type=vhost-user,id=mynet2,chardev=char2,vhostforce,queues=2 \
    -device virtio-net-pci,mac=00:00:00:00:00:02,netdev=mynet2,mq=on,vectors=6

Note

Queue value above should match the queues configured in OVS, The vector value should be set to "number of queues x 2 + 2"

Configure the guest interface

Assuming there are 2 interfaces in the guest named eth0, eth1 check the channel configuration and set the number of combined channels to 2 for virtio devices:
```
$ ethtool -l eth0
$ ethtool -L eth0 combined 2
$ ethtool -L eth1 combined 2
```
More information can be found in vHost walkthrough section.

Configure kernel packet forwarding

Configure IP and enable interfaces:

$ ifconfig eth0 5.5.5.1/24 up
$ ifconfig eth1 90.90.90.1/24 up

Configure IP forwarding and add route entries:

$ sysctl -w net.ipv4.ip_forward=1
$ sysctl -w net.ipv4.conf.all.rp_filter=0
$ sysctl -w net.ipv4.conf.eth0.rp_filter=0
$ sysctl -w net.ipv4.conf.eth1.rp_filter=0
$ ip route add 2.1.1.0/24 dev eth1
$ route add default gw 2.1.1.2 eth1
$ route add default gw 90.90.90.90 eth1
$ arp -s 90.90.90.90 DE:AD:BE:EF:CA:FE
$ arp -s 2.1.1.2 DE:AD:BE:EF:CA:FA

Check traffic on multiple queues:

$ cat /proc/interrupts | grep virtio

vHost Walkthrough

Two types of vHost User ports are available in OVS:

vhost-user (dpdkvhostuser)
vhost-user-client (dpdkvhostuserclient)

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, dpdkvhostuser or 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.

vhost-user

Install the prerequisites:
- QEMU version >= 2.2
Add vhost-user 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 name of the port type is dpdkvhostuser:
```
$ 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. More instructions on this can be found in the next section "Adding vhost-user ports to VM"
Note

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`
```
Add vhost-user ports to VM
1. Configure sockets
  
  Pass the following parameters to QEMU to attach a vhost-user device:
```
-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
```
  where 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 path and id as necessary. Note that a separate and different chardev path 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
```
1. Configure hugepages
  
  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
```
2. Enable multiqueue support (optional)
  
  QEMU needs to be configured to use multiqueue:
```
-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
```
  where:
  
  $q
  
  The number of queues
  
  $v
  
  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 configuration of n_rxq is not supported because OVS will work properly only if 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 $q.
  
  For example, this can be done for the Linux kernel virtio-net driver with:
```
$ ethtool -L <DEV> combined <$q>
```
  where:
  
  -L
  
  Changes the numbers of channels of the specified network device
  
  combined
  
  Changes the number of multi-purpose channels.

Configure the VM using libvirt

You can also build and configure the VM using libvirt rather than QEMU by itself.

Change the user/group, access control policty and restart libvirtd.
- In /etc/libvirt/qemu.conf add/edit the following lines:
```
user = "root"
group = "root"
```
- Disable SELinux or set to permissive mode:
```
$ setenforce 0
```
- Restart the libvirtd process, For example, on Fedora:
```
$ systemctl restart libvirtd.service
```
Instantiate the VM
- Copy the XML configuration described in the DPDK installation guide.
- Start the VM:
```
$ virsh create demovm.xml
```
- Connect to the guest console:
```
$ virsh console demovm
```
Configure the VM

The demovm xml configuration is aimed at achieving out of box performance on VM.
- The vcpus are pinned to the cores of the CPU socket 0 using vcpupin.
- Configure NUMA cell and memory shared using memAccess='shared'.
- Disable mrg_rxbuf='off'

Refer to the libvirt documentation for more information.

vhost-user-client

Install the prerequisites:
- QEMU version >= 2.7
Add vhost-user-client ports to the switch.

Unlike vhost-user ports, the name given to port does not govern the name of the socket device. vhost-server-path reflects the full path of the socket that has been or will be created by QEMU for the given vHost User client port.

For vhost-user-client, the name of the port type is dpdkvhostuserclient:
```
$ VHOST_USER_SOCKET_PATH=/path/to/socker
$ ovs-vsctl add-port br0 vhost-client-1 \
    -- set Interface vhost-client-1 type=dpdkvhostuserclient \
         options:vhost-server-path=$VHOST_USER_SOCKET_PATH
```
Add vhost-user-client ports to VM
1. Configure sockets
  
  Pass the following parameters to QEMU to attach a vhost-user device:
```
-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
```
  where 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 Backend Inside VM

Additional configuration is required if you want to run ovs-vswitchd with DPDK backend inside a QEMU virtual machine. Ovs-vswitchd creates separate DPDK TX queues for each CPU core available. This operation fails inside QEMU virtual machine because, by default, VirtIO NIC provided to the guest is configured to support only single TX queue and single RX queue. To change this behavior, you need to turn on mq (multiqueue) property of all virtio-net-pci devices emulated by QEMU and used by DPDK. You may do it manually (by changing QEMU command line) or, if you use Libvirt, by adding the following string to <interface> sections of all network devices used by DPDK:

<driver name='vhost' queues='N'/>

Where:

N: determines how many queues can be used by the guest.

This requires QEMU >= 2.2.

QoS

Assuming you have a vhost-user port transmitting traffic consisting of packets of size 64 bytes, the following command would limit the egress transmission rate of the port to ~1,000,000 packets per second:

$ ovs-vsctl set port vhost-user0 qos=@newqos -- \
    --id=@newqos create qos type=egress-policer other-config:cir=46000000 \
    other-config:cbs=2048`

To examine the QoS configuration of the port, run:

$ ovs-appctl -t ovs-vswitchd qos/show vhost-user0

To clear the QoS configuration from the port and ovsdb, run:

$ ovs-vsctl destroy QoS vhost-user0 -- clear Port vhost-user0 qos

Refer to vswitch.xml for more details on egress-policer.

Rate Limiting

Here is an example on Ingress Policing usage. Assuming you have a vhost-user port receiving traffic consisting of packets of size 64 bytes, the following command would limit the reception rate of the port to ~1,000,000 packets per second:

$ ovs-vsctl set interface vhost-user0 ingress_policing_rate=368000 \
    ingress_policing_burst=1000`

To examine the ingress policer configuration of the port:

$ ovs-vsctl list interface vhost-user0

To clear the ingress policer configuration from the port:

$ ovs-vsctl set interface vhost-user0 ingress_policing_rate=0

Refer to vswitch.xml for more details on ingress-policer.

Flow Control

Flow control can be enabled only on DPDK physical ports. To enable flow control support at tx side while adding a port, run:

$ ovs-vsctl add-port br0 dpdk0 -- \
    set Interface dpdk0 type=dpdk options:tx-flow-ctrl=true

Similarly, to enable rx flow control, run:

$ ovs-vsctl add-port br0 dpdk0 -- \
    set Interface dpdk0 type=dpdk options:rx-flow-ctrl=true

To enable flow control auto-negotiation, run:

$ ovs-vsctl add-port br0 dpdk0 -- \
    set Interface dpdk0 type=dpdk options:flow-ctrl-autoneg=true

To turn ON the tx flow control at run time(After the port is being added to OVS):

$ ovs-vsctl set Interface dpdk0 options:tx-flow-ctrl=true

The flow control parameters can be turned off by setting false to the respective parameter. To disable the flow control at tx side, run:

$ ovs-vsctl set Interface dpdk0 options:tx-flow-ctrl=false

pdump

Pdump allows you to listen on DPDK ports and view the traffic that is passing on them. To use this utility, one must have libpcap installed on the system. Furthermore, DPDK must be built with CONFIG_RTE_LIBRTE_PDUMP=y and CONFIG_RTE_LIBRTE_PMD_PCAP=y.

Warning

A performance decrease is expected when using a monitoring application like the DPDK pdump app.

To use pdump, simply launch OVS as usual. Then, navigate to the app/pdump directory in DPDK, make the application and run like so:

$ sudo ./build/app/dpdk-pdump -- \
    --pdump port=0,queue=0,rx-dev=/tmp/pkts.pcap \
    --server-socket-path=/usr/local/var/run/openvswitch

The above command captures traffic received on queue 0 of port 0 and stores it in /tmp/pkts.pcap. Other combinations of port numbers, queues numbers and pcap locations are of course also available to use. For example, to capture all packets that traverse port 0 in a single pcap file:

$ sudo ./build/app/dpdk-pdump -- \
    --pdump 'port=0,queue=*,rx-dev=/tmp/pkts.pcap,tx-dev=/tmp/pkts.pcap' \
    --server-socket-path=/usr/local/var/run/openvswitch

server-socket-path must be set to the value of ovs_rundir() which typically resolves to /usr/local/var/run/openvswitch.

Many tools are available to view the contents of the pcap file. Once example is tcpdump. Issue the following command to view the contents of pkts.pcap:

$ tcpdump -r pkts.pcap

More information on the pdump app and its usage can be found in the DPDK docs.

Jumbo Frames

By default, DPDK ports are configured with standard Ethernet MTU (1500B). To enable Jumbo Frames support for a DPDK port, change the Interface's mtu_request attribute to a sufficiently large value. For example, to add a DPDK Phy port with MTU of 9000:

$ ovs-vsctl add-port br0 dpdk0 \
  -- set Interface dpdk0 type=dpdk \
  -- set Interface dpdk0 mtu_request=9000`

Similarly, to change the MTU of an existing port to 6200:

$ ovs-vsctl set Interface dpdk0 mtu_request=6200

Some additional configuration is needed to take advantage of jumbo frames with vHost ports:

mergeable buffers must be enabled for vHost ports, as demonstrated in the QEMU command line snippet below:

-netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce \
-device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,mrg_rxbuf=on

Where virtio devices are bound to the Linux kernel driver in a guest environment (i.e. interfaces are not bound to an in-guest DPDK driver), the MTU of those logical network interfaces must also be increased to a sufficiently large value. This avoids segmentation of Jumbo Frames received in the guest. Note that 'MTU' refers to the length of the IP packet only, and not that of the entire frame.

To calculate the exact MTU of a standard IPv4 frame, subtract the L2 header and CRC lengths (i.e. 18B) from the max supported frame size. So, to set the MTU for a 9018B Jumbo Frame:
```
$ ifconfig eth1 mtu 9000
```

When Jumbo Frames are enabled, the size of a DPDK port's mbuf segments are increased, such that a full Jumbo Frame of a specific size may be accommodated within a single mbuf segment.

Jumbo frame support has been validated against 9728B frames, which is the largest frame size supported by Fortville NIC using the DPDK i40e driver, but larger frames and other DPDK NIC drivers may be supported. These cases are common for use cases involving East-West traffic only.

vsperf

The vsperf project aims to develop a vSwitch test framework that can be used to validate the suitability of different vSwitch implementations in a telco deployment environment. More information can be found on the OPNFV wiki.

Bug Reporting

Report problems to bugs@openvswitch.org.

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